Chemical Control of Elodea Densa Planch. and Other Submersed Aquatic Plants As Influenced by Several Environmental Factors

AN ABSTRACT OF THE THESIS OF

JOHN WILLIAM MACKENZIE for the DOCTOR OF PHILOSOPHY (Name) (Degree) in FARM CROPS presented on 5-j/q70 (Major) (Date-) Title: CHEMICAL CONTROL OF ELODEA DENSA PLANCH. AND

OTHER SUBMERSED AQUATIC PLANTS AS INFLUENCED

BY SEVERAL ENVIRONMENTAL FACTORS Abstract approved: Redacted for Privacy W. R. Furtick

Elodea densa Planch. was exposed to diquat (6, 7 dihydrodipyri-

[do1,2-a:2',11-c]pyrazinediium dibromide), alone and in combination with disodium endothall (disodium salt of 7-oxabicyclo[2.2.1] heptane-2, 3-dicarboxyclic acid), and copper sulfate pentahydrate. Studies were conducted in coastal lakes of Oregon infested with E. densa.Dichlobenil (2, 6 dichlorobenzonitrile) was applied following diquat treatments in an attempt to extend length of the control period. Plant samples were collected from trials in Siltcoos Lake for diquat analysis.Laboratory studies were conducted to determine the effects of water temperature, exposure time, light quality, and time of application on the activity of diquat and diquat combinations against E. densa.Weights of stem, length of stem, and visual control evaluations were used to measure effectiveness of herbicide application. In field trials, effective seasonal control of E. densa was achieved by application of 0.25 ppmw diquat.Addition of 0.25 ppmw endothall or 0.5 ppmw copper sulfate pentahydrate did not enhance the activity of the 0.25 ppmw rate of diquat.The optimum elodea control from 1.0 ppmw diquat did not prevent extensive regrowth the following season.Dichlobenil at 10 and 20 pounds active per acre suppressed but did not completely prevent regrowth in previously diquat-treated plots.Levels of diquat in treated plants were not increased by addition of endothall or copper sulfate.The influence of water movement in Siltcoos Lake from wind and flood water resulted in drift of chemical from treated areas and consequent control of exposed E. densa over significant untreated areas. In the laboratory, preliminary trials demonstrated that submersed plants native to the coastal lakes, Elodea canadensis Michx., Ceratophyllum demersum L., and Myriophyllum verticillatum L. were effectively controlled by 0.25 ppmw diquat as was E. densa. Addition of 0.25 ppmw disodium endothall or 0.5 ppmw copper sulfate pentahydrate did not improve E. densa control with 0.25 ppmw diquat except at 30 C where the diquat-endothall combination was superior. As the water temperature was reduced from 30 C to 20 C to 10 C, expression of the phytotoxicity of diquat was delayed but not prevented. When E. densa was exposed to 0.25 ppmw diquat alone or in combination with 0.25 ppmw endothall, six hours at 30 C and 24 hours at 20 C and 10 C were required for optimum control.At 10 C, the diquat- endothall combination and, at 20 and 30 C, the diquat-copper sulfate combination was less effective than 0.25 ppmw diquat alone. When E. densa was grown under the visible light spectrum (360- 740 mp.), the red band (620-740 mp.), the green band (440-620 mg), and the blue band (360-560 mp.) phytotoxicity of diquat, alone or in combination, was not affected.Application of 0.25 ppmw diquat, alone or in combination with 0.5 ppmw copper sulfate, was most effective for control of E. densa at the beginning or middle of the 12 hour photoperiod rather than at the beginning or middle of the 12 hour dark period. Chemical Control of Elodea densa Planch. and Other Submersed Aquatic Plants as Influenced by Several Environmental Factors

by John William Mackenzie

A THESIS submitted to Oregon State University

in partial fulfillment of the requirements for the .degree of Doctor of Philosophy

June 1971 APPROVED:

Redacted for Privacy Professor of Crop Science in charge of major

Redacted for Privacy

Head7rDepartment of Farm Crops

Redacted for Privacy

Dean of Graduate School

Date thesis is presented Typed by Donna L. Olson for John William Mackenzie ACKNOWLEDGEMENTS

The author wishes to give thanks and appreciation to Dr. W. R. Furtick, his major professor, for having the author back to work on his Ph.D. and for his invaluable counsel. Dr. A. P. Appleby for help with technical and financial problems at all times. Dr. C. E. Bond and V. Van Volk for serving on the graduate committee and for wise counsel on research matters and the writing of this thesis. Mr. E. T. Juntunen, without whose friendship and technical assistance, this thesis could not have been written. Dr. D. P. Moore for serving on the graduate committee. The Environmental Health Science Center, Dr. V. H. Freed and Dr. I. J. Tinsley for providing financial support and intellectual stimulation during the conduct of the graduate program. Mr. J. Mc Kern and Mr. W. Weber, Jr. for technical assistance. Finally, to the author's wife, Donna Jay, for surviving the graduate program, three rugby seasons and still having enough strength to type the rough drafts of this thesis. TABLE OF CONTENTS

Page

INTRODUCTION 1

LITERATURE REVIEW 4

I.Aquatic Plants and Their Habitat 4 II.Description of Four Submersed Hydrophytes: E. densa, E. canadensis, C. dermersum, and M. verticillatum 10 III.Biotic Relationships of Aquatic Plants 15 IV.The Coastal Lakes of Oregon 20 V.Control of Submersed Aquatic Plants 25 VI.Aquatic Herbicides:Diquat, Endothall, Copper Sulfate, and Dichlobenil 30 VII.Herbicide Combinations in Aquatic Weed Control 66 VIII.Recreational Values and Economic Justification for Aquatic Plant Control Programs 69

MATERIALS, METHODS, AND RESULTS 73 Laboratory Trials 73 Field Trials 88

DISCUSSION AND CONCLUSIONS 112

BIBLIOGRAPHY 125

APPENDIX 142 LIST OF FIGURES

Figure Page

1. Location of lakes infested with E. densa in Oregon. 21

2. Structures of diquat, endothall, dichlobenil, and copper sulfate. 33

3. Diagram of Field Trial 1, South Ten Mile Lake, 1968-1970. 93

4. Diagram of Field Trial 2, Siltcoos Lake, 1969-1970. 98

5. Diagram of Field Trial 3, Siltcoos Lake, 1969-1970. 106

6. Map of Siltcoos Lake showing location of Field Trial 2, Field Trial 3, and the proposed pilot study in Keichle Arm. 123

LIST OF APPENDIX FIGURES

1. Transmission of visible light through four Rohm and Haas plexiglas filters. 142 LIST OF TABLES

Table Page

1. Extent of infestation of E. densa in Oregon lakes. 23

2. Effect of time of application of various chemical treatments on control of E. densa. 79

3. Effect of time of exposure of two chemical treatments on control of E. densa. 82

4. Effect of light quality and chemical treatments on control of E. densa. 85

5. The effect of temperature and light quality on the activity of diquat and diquat combination treatments on E. densa control at 10 days after application. 87

6. Herbicide treatments made in Field Trial 1, South Ten Mile Lake, 1968 and 1969. 94

7. Control of E. densa in Field Trial 1, Booth Arm, Siltcoos Lake, 1968-1970. 96

8. Control of E. densa in Field Trial 2, Booth Arm, Siltcoos Lake, 1969-1970. 102

9. Diquat content in E. densa after treatment with diquat; Field Trial 2, Booth Arm, Siltcoos Lake, 1969. 104

10. Control of E. densa in Field Trial 3, Fiddle Creek Arm, Siltcoos Lake, 1969-1970. 108

11. Diquat content in E. densa after treatment with diquat; Field Trial 3, Siltcoos Lake. 110 LIST OF PLATES

Plate Page

1. Roots and stems of Elodea densa from Tahkenitch Lake. 11

2. Elodea densa infestation in Fiddle Creek Arm, Siltcoos Lake, 1969. 11

3. Typical plot in preliminary screening trial, Fairplay Laboratory, 1969. 75

4. Control of Elodea densa with diquat at 0.5 ppmw. Control plot on right. 75

5. Wooden water baths with experimental jars, Fairplay Laboratory, 1969. 77

6. Metal water baths showing arrangement of lamps and polyethylene screening, Fairplay Laboratory, 1969. 77

7. Application of experimental herbicide (SD 15179) by author in Booth Arm, Siltcoos Lake, 1969. 91

8. Control of Elodea densa with diquat at 1.0 ppmw, Field Trial 3, Fiddle Creek Arm, October 1969. 91

9. East side of Booth Arm, Siltcoos Lake showing control of Elodea densa along shore line due to diquat application and drift, Field Trial 2, September 1969. 101

10. West side of Booth Arm, Siltcoos Lake showing typical Elodea densa infestation, September 1969. 101 CHEMICAL CONTROL OF ELODEA DENSA PLANCH. AND OTHER SUBMERSED AQUATIC PLANTS AS INFLUENCED BY SEVERAL ENVIRONMENTAL FACTORS

INTRODUCTION

Aquatic vascular plants represent a minority of the vascular plants of the world, albeit a specialized minority (143).In the course of the past century, growth of certain aquatic plant species has interfered drastically with human activities.By so doing, these species have become "weeds". These disruptions have been documented on a world-wide basis (181) for the U.S.A. (1963), and for Oregon (25). Submersed vascular plants have assumed greater importance recently as eutrophication of natural and manmade water systems has increased (40, 70, 102).Both Holm (81) and Timmons (163) specifically mention Elodea densa Planch., Elodea canadensis Michx., Ceratophyllum demersum L., and Myriophyllum sp. as problem plants. When these and other submersed plants are present in sufficient quantity, they conflict with human activities by interfering with navigation, recreation, fish production, drainage, and public health safety.It must be stressed that such plants represent shelter for fauna, substrates for microfloral and faunal growth, a source of oxygenation to the water, feed for fish and wildfowl, visual amenity, and possible pollution traps.Mackenthun (102) stated it precisely as follows: 2 Aquatic vegetation has a definite role in the development and maintenance of a balanced aquatic community. A certain amount of aquatic vegetation in a given body of water is of value to the fishery and wildfowl, although no one has determined the proportion of plant area to water area that is necessary for optimum fish production. Control of excessive plant growth has long been practiced by man (164).Mechanical, biological, and chemical methods are utilized for control of aquatic as well as terrestrial plants.Economic pressures have led to a major emphasis on the use of chemicals as opposed to the other techniques.This emphasis on the use of chemicals has come under severe criticism by virtue of possible hazards of pesticide use and because ecologists (40, 70) feel that use of chemicals only temporarily assuages the problem of excessive plant growth. Timmons (164) indicates that the "search for herbicides for control of aquatic and bank weeds has been virtually halted". With this background, E. densa growth in the coastal lakes of Oregon can be considered.Pitney (132), writing in 1948, claimed that the waters of Western Oregon were in jeopardy from invasion by this plant.By 1955, it was reported (25) that the 7200 acres of major coastal lakes were almost completely infested with E. densa during the summer months.In recent years, growth of E. densa continued at nuisance levels. By virtue of the valuable sport-fishery resource present in the lakes, chemicals toxic to fish and other fauna are not acceptable as E. densa control measures.In the past decade, 3 progress has been made in developing herbicides suitable for use in the aquatic environment with a minimum of hazard (6, 91, 168). The objectives of the thesis research were:

1) to present available information on problems and benefits associated with aquatic vascular growth and its control, with emphasis on conditions in the Oregon coastal lakes.

2) to investigate the effects of environmental factors, time of application,and chemical additives on the activity of diquat (6, 7 dihydrodipyrido [1, 2-a: 2', 11-c] pyridinediium ion) against E. densa and other submersed plants.

3) to develop a safe, practical herbicidal treatment for control of E. densa in the coastal lakes. 4 LITERATURE REVIEW

I.Aquatic Plants and Their Habitat

Characteristics of Aquatic Plants

Differentiation of aquatic plants from terrestrial plants is not an easy task when emergent aquatic species are considered.But submersed plants can be readily classified by the presence of completely submerged foliage.These hydrophytes are separated by Sculthorpe (143) into caulescent, rosette and thalloid types.The return of these plants to water from their original terrestrial environment has led to certain physiological advantages and problems. The need for mechanical support is alleviated in water.Paucity of lignin and lack of sclerenchyma are characteristic of submersed plants.In reaction to lack of excessive solar radiation, as with terrestrial shade plants, submersed plants possess thin leaves, thin cuticles, and epidermal chloroplasts.Oxygen, carbon dioxide, and nutrients can be more readily assimilated through these thin cuticles. Reproduction is primarily vegetative in the monocotyledonous Hydrocharitaceae, and the dicotyledonous Ceratophyllaceae, and Haloragaceae.This is common in hydrophytes.Detached node fragments, stem portions bearing a bud, or dormant apices consisting of dense clusters of apical leaves remain viable over winter to form new 5 individuals the following spring.Even where flowers are regularly formed, as with E. densa (143), viable seed is not formed as all plants found in alien ranges are male.Vegetative reproduction and spread can be rapid in exotic habitats as evidenced by spread of various members of the Hydrocharitaceae in Florida (20), Oregon (132), New Zealand (106), and Great Britain (143).

Production of Aquatic Plants

Communities of submersed plants are not overly productive, although standing crops of plants may be great (143).The range of production per hectare per year is from one to seven metric tons. Biomass in the aquatic environment can be substantial.In subtropical Florida, a 21,340 kg/ha crop of fresh Hydrilla verticillata Victorin was recorded (21) while intemperate Wisconsin, C. demersum yielded 5200 to 6800 kg/ha.These monospecific colonies tended to resist invasion by other species and maintained themselves as closed communities. Submersed hydrophytes have been investigated as a source of foodstuffs (7) or fertilizer (25, 40, 78).It has been shown that E. canadensis of low fibre content (118) may have crude protein levels of 21% while E. densa may have 16.8% (7).These levels compare favourably with dehydrated alfalfa meal. Recent studies by Boyd (82) have shown E. densa and C. demersum to contain 18% crude protein 6 on a dry weight basis with Myriophyllum sp. at the 12 to 18% level. Crude protein levels decreased with age as occurred with high quality forage crops.Both Boyd and New Jersey workers (133) have noted the necessity of dehydration for processing aquatic plants.

Nutrient Factors Affecting Aquatic Plant Growth

Levels of nutrients known to be essential for aquatic plant growth vary greatly in natural waters (102).Levels of 0.5 mg /1N and 0.005 mg/1 P have supported excellent plant growth in experimental ponds (116).Disagreement exists on the importance of water-based nutrients in production and composition of aquatic plants. Levels of nutrients can be high in ground water.In Wisconsin (102), total phosphorous levels varied from 0.002 to 0.197 mg/1 while nitrogen levels were reported as high as 3.45 mg/l. Lakes fed from such a groundwater supply will be eutrophic.Fish (34), working in New Zealand, reported that composition of E. canadensis reflected the quality of water in which it was grown.In an oligotrophic habitat,

N,P, and K levels were half those found in plants growing under eutrophic conditions.Recent studies in New York (116, 117) demonstrated increased production of E. canadensis as levels of N and P in pond water were raised to 0.172 and 0.065 mg/l. Once these optimum water-based nutrient levels were surpassed, increase in growth of E. canadensis was related more to the type of hydrosoil than to 7 nutrient levels in the water.Less growth was recorded when sand re- placed soil; increased N and P water levels on sand substrate only partially increased plant growth to levels attained on soil substrate with similar nutrient levels. No studies on micronutrients were recorded.In Wisconsin (63), plant composition in eutrophic lakes demonstrated higher N and P levels than in plants from oligotrophic bodies of water.Differences between plant species, related to variation in root penetration and capacity to absorb nutrients, made it impossible to correlate plant production specifically to nutrient levels in the water.Peltier and Welch (128, 129) concluded, on the basis of laboratory and field studies with Potamogeton crispus L. and Najas sp., that plant biomass was directly related to nutrient levels in the substrate rather than the water.In Pickerel Reservoir, Alabama, plant production was lowest in years when N and P levels were at a maximum in the water. N and P levels can influence phytoplankton production to the extent that vascular plant communities may be shaded out (25, 116, 117).

Effect of Light and Temperature on Aquatic Plant Growth

Light is an important and variable factor (21) required for photosynthesis by submersed plants.Attenuation of light in water varies greatly from one lake to another and from one time of the year to another by virtue of turbidity, macro and microfloral abundance, 8 and soluble materials (102).The zone of photosynthesis for aquatic plants, the euphotic zone, extends to the depth where 1% of incident radiation penetrates. The solar spectrum incident on plant foliage is changed qualita- tively as well as quantitatively by the water through which it passes. Attenuation of infrared and ultraviolet radiation is complete in the upper 10 cm, of distilled water (179).Algal blooms attenuate those wavelengths of light associated with photosynthetic pigment absorbance; the 430 mp. and 660 mp. maxima (143).English work (179), in dense beds of aquatic plants, demonstrated that vascular hydrophytes absorbed light at both ends of the visible spectrum; red (above 580 mp.) and blue (below 480 rnp.) light.At 20 cm, in Ranunculus sp. beds, only 0. 1% of the incident surface light was recorded.The residual light was entirely of green wavelengths from 480 to 550 mp..Below 30 cm, in the dense plant communities, light was not measurable. The surface light was equally divided between blue, green, and red bands. Within the upper portions of the plant beds, over 50% of incident light is in the green band.Westlake (180) commented that, "while colour of light transmitted through water will have some effect on photosynthesis, it is unlikely to be of practical importance". Presence of organic solutes in the water results in loss of blue, violet, and ultraviolet radiation (143).Laboratory experiments showed (80) that red light caused increased shoot development and internode 9 elongation of Potamogeton pectinatus L.Similar studies with E. densa (16) showed optimum growth under red light and limited growth under blue and green light. Intensity of incident light was not thought to limit photosynthesis in early studies (108, 109) but, more recently, inhibition of photosynthesis by "solarization" or bleaching of terminal portions of E. densa and H. verticillata (16, 21) in temperate and subtropical climates has been reported.Studies in England (127) and the U.S.A. (128) have noted declines in vascular plant growth under conditions of diminished light intensity.Studies in Wisconsin (142) indicated that, on dull days, optimum photosynthesis in E. canadensis and C. demersum occurred at the surface whereas on bright days the optimum depth was five meters. Bluegreen algal blooms were responsible for reducing light transmission from 5 to 2. 5%.This affected vegetative growth in July and August under English conditions (127). Periods of heavy rains and overcast skies in Alabama were corre- lated with a decline in growth of P. pectinatus L. (128). Temperature fluctuates less drastically in the aquatic environment than it does on land.Major submersed species have a wide range of temperature tolerance as shown by the distributionof these species in many different climatic zones (143).E. densa will survive at 6 C in Oregon (25) and at 30 C in Florida (21).Similar ranges exist for C. demersum (21) and Myriophyllum sp. (114). 10

II.Description of Four Submersed Hydrophytes: E. densa, E. canadensis, C. dermersum, and M. verticillatum

Elodea densa Planch., Brazilian Waterweed

E. densa is a monocotyledonous, submersed hydrophyte in the family Hydrocharitaceae (Plate 1).It is a perennial, slender- stemmed, branching plant with whorled leaves and slender, un- branched, fibrous roots (114).E. densa has the ability to exist as a free floating plant.Leaves of E. densa are three to five mm wide, up to 40 mm long, closely spaced and sessile with serrated edges. Each leaf contains a single midrib and is translucent. Two to four flowers with 10 mm yellowish-white petals rise from a single spathe which may extend 20 mm above the water surface.In alien populations, the female flower is unknown (114).Seeds have been found but they are uncommon. Floating plant fragments and lateral growth from rootstocks are the major method of plant dispersal. St. John has placed E. densa in the genus Egeria although this subject is open to taxonomic discussion (20).E. densa is native to South America but, because of its use as an aquarium plant,it has become established throughout the world.Infestations are reported in California, Florida (20), Oregon (25), and Virginia (25) in the United States. Sculthorpe (143) has reported that E. densa is established in England, France, Germany, Italy, Japan, Kenya, Mexico, New Plate 1.Roots and stems of Elodea densa from Tahkenitch Lake, 1969.

Plate 2.Elodea densa infestation in Fiddle Creek Arm, Siltcoos Lake, 1969. 12

Zealand, and Switzerland, Under Oregon conditions (3), E. densa has become established as the dominant submersed plant in coastal lakes. Optimum growth takes place from June through August while growth ceases and "dying-back" to the rootcrown often occurs during winter months. Regrowth can occur as early as March. Both in Oregon and New Zealand, optimum growth has been observed at 18 to 20 C with a minimum growth temperature of 10 C.Light requirements for E. densa are low.Blackburn (16) reported an optimum light requirement of 10 foot candles.Silt and organic substrates are preferred to sand and gravel sites for establishment of E. densa populations.

Elodea canadensis Michx., American Waterweed

E. canadensis has the appearance of a smaller version of E. densa.The lowest leaves are opposite or in whorls of three and are much smaller than the upper leaves which can be found in whorls of three to seven.The leaves are linear to oblong, acute or obtuse, and sharply serrate,1 to 2.4 mm wide and 10 to 13 mm long (20, 114). The dioecious flowers are solitary, unlike those of E. densa and are attached to a long peducle. Seeds are rare with plant fragments representing the main dispersal mechanism. E. canadensis is native to North America.It is a commonly found plant in western, eastern, and northern states (114).The 13 plant has not been observed in Alabama, Florida, or Georgia.It established itself in Europe in the 19th century where it created the first recorded submersed plant growth problem by infesting barge canals (143). In Oregon, E. canadensis is found in shallow water (25) where E. densa is not established.The temperature range of this plant appears to be narrower than for E. densa in that it does not occur in subtropical waters (20).Excellent growth has been reported at light intensities of 50 to 200 foot candles with probable light saturation occurring at 200 to 300 foot candles (45).

Ceratophyllum demersum L. ,Coontail

This dicotyledonous plant is found in the family Ceratophyllaceae which consists of one genus containing six species.C. demersum is a submersed, rootless, olive-green to green perennial herb which possesses a slender main axis with scattered lateral branches.The lower end of the stem is frequently buried in mud and is without chlorophyll.The leaves are in whorls and are dichotomously dis - sected, often stiff and brittle.The leaf whorls are crowded towards the apex by shortening of the internodes, giving the shoot the appearance of a "coontail".The plants are monoecious with reduced male and female flowers on different nodes. Dispersal of C. demersum is either by seed or by the 14 overwintering of thickened apical segments which act as winterbuds (114, 143).Growth is mainly as an anchored plant but the freefloating habit is found.C. demersum is a cosmopolitan species, found in every state of the U.S.A.

Myriophyllum verticillatum L., Whorled Watermilfoil

M. verticillatum is a perennial, dicotyledonous, submersed hydrophyte in the family Haloragaceae.It has a lax, slender stem. The submersed leaves are 10 to 45 mm long, whorled in groups of four to five,and are filiformly divided.The emergent leaves are pinnately dissected and opposite when present.The roots freely divide from lower nodes.Plants are monoecious with the male flowers above the female on the emergent spike. M. verticillatum is commonly found in Oregon along the edges of currents made by streams entering lakes.Distribution is confined to the Northern United States. 15 III.Biotic Relationships of Aquatic Plants

The natural water ecosystem is a classical example of the relationship of organisms with themselves and their environment.Tro- phic levels are recognizable and inter-relationships demonstrable. The first trophic level consists of producer organisms.Phytoplank- ton, filamentous algae, and vascular plants combine products of photosynthesis and available nutrients to create a biomass available to consumer organisms.These second and third trophic levels consist of zooplankton, microcrustaceans, invertebrates, and herbivorous fishes at the second and carnivorous fishes at the third level.If man harvests and consumes fish from the system then yet another trophic level is added.The maintenance of this structure depends on the availability of food produced by photosynthetic organisms and the recycling of nutrients.Sculthorpe (143), has identified the problem faced in management of aquatic vascular plants.He states that a balance should be aimed at between excess and shortage.It is then admitted that quantitative information is not available. Needham (117) states it succinctly as follows, "A moderate amount of vegetation can be very useful, but it is often difficult to establish and maintain plant growth in properly controlled abundance". 16 Beneficial Relationships

The beneficial relationships of vascular plants to microflora and fauna have been considered by various workers.Plants with dissected, whorled foliage are known to offer vast potential surfaces for colonization by epiphytic organisms such as desmids, diatoms, and filamentous algae.Plant surface to bottom surface ratios can be as wide as 30 to 50 to 1 (143).Differences in associated fish-food organism populations have been demonstrated between aquatic plants with different plant surface to bottom surface ratios.In a New York stream (117), beds of Chara sp., a plant-like alga with numerous finely divided "leaves", was shown to support 3400 kg of organisms per hectare.Plants with broad linear leaves and lower surface area such as Potamogeton crispus L. supported but 500 kg per hectare. Moyle (113), in central Minnesota, found three times the weight of bottom fauna associated with "weedy" as opposed to "non-weedy" areas; snails, insects, and mussels were 5,10, and 15 times more abundant. Growth of trout is known to be favoured by increased insect populations (50).Midge and mayfly Larvae were found in association with aquatic plant beds (117).Copepods, ostracods, and mollusks were all closely associated with E. canadensis beds according to Hilsenhoff (75).The same plant, in another study (102), was rated as an excellent habitat for fish-food organisms.It provided a potential 17 food supply six times that of a bottom substrate void of vascular plants.In the Tennessee Valley, Myriophyllum spicatum L. was shown to be the habitat of immature midges, mayflies, and dragon- flies.Elimination of the habitat resulted in loss of these invertebrates.Hilsenhoff (75), in Wisconsin, noted a similar phenomenon when E. canadensis was eliminated.In Oklahoma (22), loss of habitat was held responsible for a reduction in fish productivity.Disintegra- tion of vascular plants which occurs naturally or deliberately, in- creases bottom organic matter (69) with a resultant increase in populations of Tendipids and Oligochaetes.Vascular plants also provide shelter for immature fishes (102, 143).Quantitative determination of the optimum density of aquatic plants in various environments has not been accomplished (100).

Detrimental Relationships

Documentation is also available on the detrimental effects of excessive vascular plant growth.In controlled pond studies, growth of E. canadensis was shown to decrease phytoplankton and rotifer populations. Several workers state that greater fish production can be achieved by favoring phytoplankton production over growth of vascular plants (41, 95, 97, 173).This effect has been demonstrated readily in farm ponds. Smith and Swingle (149) state that, 18 as weeds disappear (owing to phytoplankton blooms), the largemouth bass and other carnivorous species are able to catch the small fish and the food for these species becomes in effect, more abundant. As a result, fish grow at a greatly increased rate and fishing is improved. In New York farm ponds (41) and in studies by Lawrence (95) and Leonard (97), excessive vegetation prevented adequate predation by bass on bluegills and shiners, thus causing a reduction in production. In one of the few controlled studies, Bennett (12) demonstrated that fish harvest was reduced by 43% despite an increase in angling intensity after open water was reduced by 50% due to dense growth of Potamogeton sp.DiCostanzo (48) noted a decrease in abundance of abundance of bluegills as density of aquatic vegetation increased.In summary, it is certain that a balanced population of vascular plants is desirable and that dense growths occupying whole bodies of water are undesirable.It is not certain where this point of balance rests.

Food for Wildlife

Vascular plants are valuable sources of food for wildfowl. Martin and Uhler (105), in their classical treatise, reviewed information on all important plants in the U.S.A. They found the contributions of Elodea sp., Ceratophyllum sp., and Myriophyllum sp. to be no more than fair.C. demersum contributed 1.04% to total game duck food and other species contributed less than 1%. Other observations (25, 143) indicate that Elodea sp. represent a food resource for 19 coots, ducks, geese, and swans.Cattle have been observed to graze E. canadensis in New Zealand (54). Some efforts (7, 132) have been made to investigate the utility of plants such as E. densa for livestock food.These efforts have not expanded into commercial utilization. 20

IV.The Coastal Lakes of Oregon

Freshwater lakes are not numerous in the State of Oregon.The greatest concentration of such lakes is located on the southwest coast between Florence and Coos Bay. Growth of vascular plants in the lakes shown in Figure 1 has been extensive (Plate 1).

History of E. densa Infestations and Control Projects

The exact date of the introduction of E. densa into the coastal lakes was not documented.Pitney (132) thought that the plant "probab- ly found its way to Oregon in the 1930's." Siltcoos Lake and Tahkenitch Lake were densely infested by 1946.The severity of the problem in these important sport fishing lakes caused political pressure to be brought on the State Legislature and the Oregon Laws of 1947 record that under Chapter 510, authority was given to the State Game Commission to control E. densa. By 1949, E. densa had been reported in the Ten Mile Lake system, Triangle and Bradley Lakes. In 1949, the Game Commission recommended that the Oregon Agri- cultural Experiment Station assume responsibility.The Game Com- mission had not established a safe, effective control technique. Under Chapter 567.035 of the Oregon Revised Statutes (138), the Oregon Agricultural Experiment Station established an Aquatic Weed Control Project led by Dr. Carl Bond. From 1949 to 1955, lakes were 21

Portland

Willamette River

PACIFIC Newport

OCEAN Corvallis

6 Triangle Lake

Florence lbEugene Siuslaw River

Siltcoos Lake

Tahkenitch Lake

North Ten Uke 0 Loon Lake W3 South Ten Mile Lake Umpqua River

Coos River Coos Bay

Figure 1.Location of lakes infested with E. densa in Oregon. 22 surveyed, chemicals screened, mechanical harvesters tested, and the ecology of E. densa studied.This program did not establish (25) an economic use for the plant or develop a completely safe, chemical technique for control.Spot-treatments to open up important fishing areas using materials toxic to the aquatic fauna were recommended. High rates of copper had given control but with deleterious effects on bottom organisms when applied at rates of 5 to 30 ppmw. Nine years later, E. densa growth was so prolific that further local pressure led to reactivation of the Aquatic Weed Control Project, under leadership of Dr. Bond. Further testing of aquatic herbicides and evaluation of biological control measures have been conducted (26, 27, 90).

Morphology and Limnology of Infested Lakes

Three major lakes, Siltcoos, Tahkenitch, and the Ten Mile Lake System, are infested with E. densa.Other smaller lakes are also infested (Table 1).Research activities reported in this thesis were concentrated in Siltcoos and Ten Mile Lakes. Organized limnological information is lacking for Oregon's coastal lakes.Information is available in Game Commission Reports (123, 137, 138, 139), Aquatic Weed Project Reports (25, 26, 27, 90) and student theses (3, 92). Located six miles south of Florence, Siltcoos Lake lies within three miles of the Pacific Ocean to which it connects via a short 23 river.The 3, 020 acre lake has a drainage area of 72 square miles including 787 acre Woahink Lake.It is located in an area of equable climate (139).

Table 1.Extent of infestation of E. densa in Oregon lakes (25). Percent lake surface area infested Lake Total acres 1946 1948 1954 1969*

Siltcoos 3020 58 74 43 60 Tahkenitch 1570 43 86 68 70 Ten Mile 2000 0 0 10 20

Loon 300 0 0 6 Triangle 280 0 8 10 10 Bradley 40 0 30 30 *authors estimate

The lake was formed by the enclosure of a coastal valley.It is a shallow, eutrophic body of water with an average depth of five meters and a maximum depth of eight meters. Shoreline development is not great.In 1964, a dam was erected by the International Paper Company of Gardiner, Oregon to stabilize water levels during the summer months. Railroad maintenance requires that, every second year, the level of the lake be dropped by five feet. On alternate years, the same practice is followed in Tahkenitch Lake. Water temperatures average from 5 to 10 C in mid-winter to 15 to 20 C in mid-summer. Strong, cooling northwest winds blow 24 from March to October during the afternoon thus preventing formation of thermoclines.Rainfall in the area averages 58 inches.Forty- eight inches of this amount falls between October to March with a corresponding reduction in incident solar radiation. Fish production in Siltcoos Lake is consistently excellent (139). The fauna is varied, both warm and cold water fishes being present. Warm water species caught include largemouth bass, yellow perch, bullhead catfish, crappie, and bluegills.Rainbow trout, cut-throat trout, coho salmon, and steelhead are .important cold water species. The bottom substrate in the lake is predominantly silt.Bottom organisms are plentiful except where copper has accumulated from previous spot treatments of copper sulfate for control of E. densa. Tendipid and Chaoborus larvae are the main benthic organisms. Sparse information is available on North and South Ten Mile Lakes (123).Located 30 miles south of Siltcoos Lake, in the same climatic area, these lakes have a total surface area of 2000 acres. The bottom is mainly mud. Water temperature ranges are similar to those in Siltcoos Lake. Complete renovation and restocking of the system was conducted during 1968 and 1969 by the Game Commission. 25 V.Control of Submersed Aquatic Plants

Dense growths of vascular aquatic plants can occur in natural and man-made waterways.Eradication of such growths has been attempted with mechanical, biological, and chemical tools.Complete control has been and is the goal of engineers responsible for opera- tion of irrigation ditches and navigation canals (81).Such policies are not acceptable in recreation and wildlife areas.Total eradication of aquatic plants is undesirable and unacceptable to organizations con- cerned with conservation (125).In the manual on vegetation control for Federal Fish and Wildlife programs, De Vaney (47) places emphasis on maintenance of the integrity of plant and animal communities. The role of vascular plants in aquatic ecosystems has previously been analyzed. Jordan (89) wrote that "we do not lack technologies to use in improvement of fish and game management but we do not put them to work".In vascular plant control, technologies are available for use; nevertheless, all facts necessary to make sound judgments on optimum plant populations for given areas are not known.

Mechanical Control

Mechanical control of aquatic plants preceded use of other techniques. Machines were developed by the U. S. Corps of Engineers (163) around 1900 in an effort to control Eichhornia crassipes (Mort) So lms., water hyacinth. Many canals and ditches are 26 still kept free of submersed plants mechanically at costs of $500 per mile (104).Machinery has been developed to cut and haul submersed plants (34).These machines can remove plants to a depth of six feet without the land-based restrictions of dragline equipment. Mechanical harvesting removes the plant biomass, and thus nutrients are removed from the water.Plant removal combined with retardation of perennial plant regrowth, will hopefully lead to an overall reduction in the infestation over a period of years. No long-term studies have been conducted to validate this rationale.Studies are presently underway at Lake Mendota, Wisconsin and in Lakes Sallie and Melissa, Detroit Lakes, Minnesota (34). Critics of mechanical control systems maintain that "per acre" costs are ten times greater than those systems which utilize approved herbicides (81).Recent information does not substantiate this claim. A U.S. D.A. report (165), issued in 1968, indicated that an average cost of $22 per acre was incurred in applying chemical control methods. These costs were for emergent plant control as well as for control of submersed vegetation.Chemical costs for application of approved herbicides such as endothall and diquat can reach $50 to $150 per acre andhigher.VMechanical harvesting costs were calculated at Maitland, Florida where $47, 000 worth of equipment was

1/Calculatedwith diquat at $20/gallon and endothall at $10/gallon. 27 utilized to harvest 20 acres of H. verticillata (34).The infestation produced 15 tons of harvested plant per acre.Cost per acre of this harvest including a ten year depreciation figure, interest charges, and labour, came to $44 per acre.Winter Park, Florida, reported (22) that repeated cutting of H. verticillata was required over the first three years of their mechanical harvesting program.

Biological Control

Development of biological control methods for control of submersed plants has lagged behind efforts towards mechanical and chemical innovations until the past decade (81).Recently major efforts have been made to utilize organisms inimical to aquatic plants. Biocontrol methods, once developed, provide control programs at low cost with relatively persistent results. Removal of nutrients from the aquatic environment is not achieved by biocontrol techniques. Aquatic snails have been utilized in research programs. Marisa cornuarietis has eliminated submersed plant growths from ponds in Florida (81) but was unsuccessful against E. densa in Oregon (90).Sensitivity to water temperatures below 6 C restricts its utility. Mammals have been employed for control of plants (81).The manatee, Trichechus manatus latirostris, has demonstrated an ability to eat submersed plants but uncertain reproductive capabilities have limited its usefulness. Fresh water fishes are used to control plant growth in 28 ponds around the world.The Chinese grass carp or white amur, Ctenophoryngodon idella, has shown promise in Oregon studies (90). Other species of fish such as Tilapia, Tilapia sp., have been effective for submersed plant control (81).Unfortunately they are also sensitive to cold water.Fishery authorities have been and are reluctant to introduce white amur and other herbivorous fish because of possible displacement of valuable sport fishes from their habitat by highly competitive, introduced species.

Chemical Control

Since 1902, when sodium arsenite was introduced to control of water hyacinth in the southern United States, the use of chemicals has proliferated.Reliable statistics are not available to document this proliferation (163).The U.S. D.A. report (165), referred to in the section on mechanical control,was incomplete because some states, including Louisiana which utilizes large amounts of aquatic herbicides, did not report.Certainly the 84, 000 acres treated in 13 states repre- sented only a portion of treated acreage (165). Since the development to 2, 4- dichlorophenoxyacetic acid, 2, 4-D, the synthesis of organic herbicides has increased greatly. Twenty herbicides are registered currently for use in aquatic environments.At this time, the search for new compounds has been virtually halted (164). 29 The use of selective and non-selective aquatic herbicides has been severely criticized since their introduction.Hasler (70) stated that affected plants rot and contribute nutrients to an already eutrophic environment.It becomes difficult to use chemicals wisely in lake ecosystems when little knowledge is available on the dynamics of these systems (71).Indiscriminate and widespread use of copper sulfate (139) and sodium arsenite (81), persistent inorganic herbicides, has added to criticisms of chemical control programs. Several aquatic herbicides such as diquat, endothall, and dichlobenil have demonstrated relative safety in the aquatic environment (1,6, 91, 168). 30 VI.Aquatic Herbicides

Recent reviews dealing with aquatic weed control have been written by Austin (6), Cope (37), Little (98), and Holm (81).It is apparent from the literature that, while laboratory and field studies have been carried out with many chemicals on many plant species, little emphasis has been placed on environmental factors which affect herbicide activity or on the use of herbicide combinations for submersed plant control.Limited information is available on factors affecting uptake and movement of herbicides in aquatic plants. A survey of "Weed Science" for the year 1969 revealed that five papers dealt with the interaction of chemicals and aquatic plants.Interac- tions of terrestrial plants and herbicides were discussed in 77 papers.

Influence of Environmental Factors on Aquatic Herbicide Activity

Temperature

Effects of temperature on several aquatic herbicides have been demonstrated. Hodgson and Otto (80) showed increased injury on P. pectinatus with xylene treatments as water temperature increased. Several workers (13, 24) in aquatic weed control have reported decreased activity of acrolein at temperatures below 15 C although Emond (51) stated that low water temperatures did not decrease effectiveness.Rate of control of E. canadensis by 31 2 -chloro -4,6, bis (ethylamine)-s -triazine, simazine,was reduced by lower water temperatures (55).Temperatures below 15 C resulted in little,if any, control from applications of 2 -(2, 4, 5, -trichloro- phenoxy) propionic acid, silvex.In this context, it was noted that susceptibility of fishes to herbicides was also increased at higher temperatures. Median Tolerance Limit (TLm) values for a, a, a, -tri- fluoro -2, 6 dinitro -N, n-dipropyl-p-toludine, trifluralin, increased from 98 to 308 ppb as the temperature was decreased from 12.7 to 1.6 C.

Light

Influence of light quality on aquatic herbicide performance on submersed plants has not been studied.Until publication of an article by Blackburn and Weldon (19) on diquat combinations in 1969, no research results on herbicide combinations were available. A detailed review of the principal herbicides used in this research project will follow.Herbicides used in combination and in field trials will be reviewed in less depth.Emphasis will be placed on:

(a)Physical and chemical properties

(b)Mode of action, uptake, and influence of environmental factors and activity

(c)Field performance on four submersed hydrophytes 32

(d)Persistence in the aquatic environment

(e)Effects on aquatic fauna and microflora.

Diquat

Diquat, 6, 7, -dihydrodipyrido (1, 2-a: 2', 1 ' -c) pyrazinediium dibromide, is a member of a group of heterocyclic organic compounds, the bipyridylium quaternary ammonium salts (Figure 2).Akhavein and Linscott (1) have completely reviewed the literature dealing with the bipyridyl herbicides.This source covers the available literature up to 1967 on the properties,structure-activity relationships, mode of action, persistence, toxicity, and field uses of diquat.

Chemical and Physical Properties

Diquat forms a pale, monohydrate solid when crystallized from solution (1, 178).Diquat is stable in aqueous acid or neutral solutions but will decompose in an alkaline solution and under ultravioletlight. Diquat is soluble in water at a level of 70 gm/100 ml but is insoluble in most organic solvents with the exception of alcohol.Diquat is formulated as a two pound per gallon aqueous solution with corrosion inhibitors added.It is manufactured in England by Imperial Chemical Industries, Ltd. 33

W.* .1111 2

2Br

C C

diquat dibromide

disodium endothall

Cl Cl

dichlob enil

CuSO4, 5F1 20

Copper sulfate pentahydrate

Figure 2.Structures of diquat, endothall, dichlobenil andcopper sulfate. 34

Mode of Action, Uptake, and Influence of Environmental Factors on Activity

Mode of Action

The mode of action of diquat is closely associated with the photosynthetic process.Essentially, the activity of diquat depends on the reduction of the cation in the plant chloroplasts to a freeradical, which, in itself,is detrimental to plant growth (1).In the presence of oxygen, the diquat free radical is reoxidized to itsoriginal form. Thus only catalytic amounts are required to cause plantdeath.The reoxidation of free radicals in the chloroplasts is thought toresult in formation of hydrogen peroxide which causes the directphytotoxicity to green tissue associated with diquat.Recent studies by Baldwin, Dodge, and Harris (8) compare the activity of bipyridylherbicides to the phenomenon of senescence in plants. It wassuggested that observed changes in the ratio of Chlorophyll A to Chlorophyll Binduced by bipyridyls closely resembled senescence patterns.Associated oxida- tion of lipids in cell membranes possibly accounted for thespeed with which these compounds act.Bipyridyl-induced phytotoxicity is more rapid in light than in dark.Under dark conditions, eventual phytotoxicity will be expressed. Under light, an increasein light intensity results in an increase in plant injury. Oxygen is also necessaryin the plant to enable reoxidation of the bipyridyl free radicaland consequent recycling of the herbicide at active sites. 35 Uptake

Uptake of diquat by submersed plants has been studied, almost exclusively under laboratory conditions.Frank and Hodgson (59) demonstrated in Potamogeton pectinatus L. that uptake and transloca- 14C tion of a foliar-active herbicide could occur.2, 4 -D was used to show movement from shoot to root and root to shoot. Funderburk and Lawrence observed a lack of diquat movement within Heteranthera dubia L. when applied either to shoots or roots

(61).Seaman and Thomas (145) used excised leaf segments of Potomogeton nodosus L. and P. pectinatus along with trifoliate nodes of E. canadensis to study diquat uptake.Uptake of diquat was rapid. In E. canadensis, the internal concentration of diquat reached 24 times that in the external solution of 0.05 ppm. Pretreatment with respiratory inhibitors, such as KCN, reduced uptake by 40%.Sixty percent of the total uptake was attributed to physical rather than metabolic processes.Davies and Seaman (44) used whole parts of E. canadensis to reveal rapid initial uptake of diquat in the first 20 minutes of exposure followed by slower, possible metabolic uptake over the following 4-1/2 hours.Trans location of diquat was equal under light and darkness.Leakage of diquat into the surrounding medium was observed from treated plants when placed in fresh water. Quantitative amounts of diquat ranging from 20 to 30 ppm were 36 taken up by submersed plants when treated with 0.5 ppmw diquat (62). Studies with H. verticillata in Florida (103) demonstrated that, under static water conditions, diquat levels in plant tissue of nine ppm were found one day after treatment with 0.5 ppmw diquat.Exposure time required for exertion of full phytotoxic effects from diquat on submersed aquatic plants in field and laboratory was shown to be 48 hours for H. verticillata at rates of 0.5 to 1.0 ppmw (103).Twenty-four hours exposure time was required in Oregon to allow one ppm diquat to completely control E. densa in the laboratory.Twelve hours was insufficient time for one ppmw but not for two ppmw diquat to achieve complete control of this plant.

Influence of Environmental Factors on Activity

There is a dearth of work conducted on the influence of environmental factors on activity of diquat on submersed plants.Information from terrestrial trials will be presented in this section. Light and Darkness.Light and darkness largely control diquat uptake and movement in plants (1).Work on Lycopersicon esculentum, tomato, by Smith and Sagar (151) showed that diquat penetrates into the leaf in both light and darkness. Widespread distribution of diquat through the plant was observed if a 24 hour dark period followed application but long distance transport required light after the long dark period.Penetration pathways seemed to be less available when diquat 37 was applied under high light intensity and uptake was correspondingly less.Brian (33), working with the same plant, observed that darkness before and after treatment increased diquat activity.The rapid phase of uptake occurred immediately after treatment. Springett (147) observed that, in field studies with bipyridyl herbicides, bright sunlight reduced the effectiveness of low application rates.In Kenya, control of Panicum sp. with bipyridyl herbicides was optimum when applied to the shaded areas of tea planta- tions (4).In other terrestrial field applications, time of day of application has influenced bipyridyl activity.Sheldrick (146) reported that control of Axonopus compressus P. Beauv. using 1, 1'-dimethy1-4, 4'-bipyridinium ion, paraquat, was accomplished with 2.6 pounds cation per acre applied 30 minutes after sunset as compared to 4.5 pounds cation per acre applied at midday.Hawaiian data (159) indicated that evening application of paraquat to Cyperus rotundus L., nutsedge, resulted in slower regrowth than noon or morning applications. Uptake of ions by submersed aquatic plants has been extensively studied by plant physiologists interested in uptake theory.Effects of light on ion uptake has been reported.Lowenhaupt (99) showed that, for submersed plants in general, calcium ion uptake occurred in light not in darkness. Jescke and Simonis (88) observed, in studies with E. densa, that uptake of the anion, H2PO4, was enhanced by light. 38 In aquatic situations, little information is available on the effects of light and darkness on diquat activity.Lemna minor L. common duckweed, was used by Blackburn and Weldon (17) to measure chlorosis induced by diquat application. As light intensity was increased from 550 lux to 16500 lux, chlorotic damage increased pro- portionately.Merkle, Leinweber, and Bovey (107) demonstrated more rapid phytotoxic effect on E. canadensis when paraquat was applied under conditions of full sunlight as opposed to 700 lux. No reading was given for "full sunlight".It is assumed that this would be at least 20, 000 lux.The more rapid effect did not result in superior control of E. canadensis.Davies and Seaman (145) exposed the same plant to 10 ppm diquat under light intensities ranging from 330 lux to 2000 lux.Effective destruction of chloroplasts was more rapid at higher intensity levels. In the field, Whitely (181) observed the best control of submersed plants with diquat when application was immediately before dark. Strykers and Timmermans (156) reported a better "systemic" effect with diquat on E. canadensis when application was made on dull, overcast days. No comparative studies with different application times were noted. Light Quality.While attention has been paid to light and darkness, light quality has been virtually ignored as an influence on diquat activity.Brian (33) noted that pretreatment of Lycopers icon 39 esculentum with red light for three hours decreased diquat injury. Blackburn and Weldon (17),treated Lemna minor L. with diquat under three different bands of the visible light spectrum, 370-520 mp. (bluegreen), 510-560 mp. (blue), and 600 mp. (orange-red).Complete chlorosis was induced by 0.1 ppm diquat under orange-red light. Under bluegreen and blue light, diquat damage levels were 40 and 60% lower than under the successful orange-red treatment. Temperature.Merkle, Leinweber and Bovey (107) demonstrated a direct influence of temperature on paraquat activity.Plant cell membrane damage increased as ambient temperature was increased.Springett (127) commented that lower ambient temperatures decreased the effectiveness of low application rates to bipyridyl herbicides. No studies in the aquatic environment relate effect of water temperature on diquat activity to submersed plants.

Hydrophyte Control

Diquat has been used as an aquatic herbicide throughout the world (6, 98).

Elodea densa Planch.

Initial screening trials in 1963 (14) showed that, with a minimum 24 hour contact time, a one ppmw diquat application gave 90% E. densa control in Florida.Further work in Oregon (26) also indicated 40 that one ppmw diquat provided satisfactory control in the laboratory, whereas application of 0.5 ppmw diquat only gave 50% control. Limited field testing of diquat at 1.0 and 2.5 ppmw in 1965 (26),

1966 (27), and 1967 (90) was conducted in Oregon Lakes.In 1965, application of one ppmw gave good "knockdown" but some regrowth was observed three weeks after application.At Ten Mile Lake in 1966, 2.5 ppmw diquat gave 100% control of E. densa.Application of 0.15 ppmw diquat, a two gallon per surface acre rate, 1967 resulted in limited "knockdown" and partial control of E. densa from the surface of Ten Mile Lake. In Florida field tests (175), 0.36 ppmw diquat, a two gallon per surface acre treatment, gave but 30% control of a dense infestation of E. densa.Complete control of 16 acres of E. densa, growing in a Virginia reservoir (39), was achieved by application of 0.45 ppmw diquat, a 1.5 gallon per surface acre rate.

Elodea canadensis Michx.

Control of this submersed plant has been achieved in California, Michigan, Oregon, and Washington with application of 0.1 to 0.25 ppmw diquat (46).In Louisiana (35), diquat at 0.25 ppmw provided control of E. canadensis after seven weeks.Hiltibran (78), working in Illinois, reported that 1.0 ppmw diquat was required to control E. canadensis.Throughout the northcentral U.S.A. (172), erratic 41 control was obtained with 0.5 ppmw diquat.In Canada, Schenk and Jarolinek (140, 141) noted that good control of E. canadensis was achieved with 0.47 ppmw diquat in Ontario farm ponds.However, in British Columbia, Hughes and Friese (84) obtained but 50% control of E. canadensis with 1.15 ppmw diquat.Field reports from Europe (23, 87, 134, 135, 166, 169, 170) indicated that rates of diquat below 1. 0 ppmw did not give consistent control of E. canadensis. Blok (23) and Van der Weij (170) both reported regrowth of E. canadensis within the season of application when 0.4 to 0.8 ppmw diquat was applied. In New Zealand (53, 121), a 0.5 ppmw treatment of diquat controlled E. canadensis at two different locations.

Ceratophyllum demersum L. and Myriophyllum verticillatum L.

Walker (172) reported successful control of these two plants throughout the northcentral U.S.A. using 0.5 ppmw diquat.One ppmw diquat gave 100% control of M. verticillatum in Oregon (27). In Canada (140), both species were controlled by 0.5 ppmw diquat. In Europe, Jennings (87) reported control at the 1.0 ppmw rate whereas in Holland (23), 0.4 to 0,8 ppmw was sufficient for control.

Summary

In an attempt to explain variability in diquat activity, Fox (56) and Yeo (186) both observed the effectiveness of soil turbidity in 42 dissipation of diquat from treated water. Fox reported that, when turbid conditions were created 24 hours after application of two ppmw diquat, all diquat detectable by the analytical technique had dis- sapeared within a few hours. Yeo also observed rapid dissipation of diquat from treated reservoirs with turbid water. Parker (124) hypothesized, on the basis of laboratory experiments with paraquat and E. canadensis, that water hardness could effect degree of control.He observed reduction in injury to E. canadensis with an increase in water hardness. Yeo (186) treated 14 reservoirs and nine growth pools with rates of diquat ranging from 0.125 to 1.0 ppmw and with hardness expressed as ppm CaCOrang- 3 ing from 26 to 209 ppm. He concluded that neither dissipation of diquat from the water nor phytotoxicity to E. canadensis, C. demersum, or Myriophyllum sp. was effected by water hardness levels.

Persistence in the Aquatic Environment

Diquat dissipates rapidly from treated water by virtue of cation absorption by phytoplankton and vascular plants, absorption to soil particles in suspension, and to the hydrosoil (145).Photochemical decomposition is also known to result in loss of diquat from water (1). Decay of treated algae and vascular plants eventually releases more diquat cation for absorption by the hydrosoil (58).Levels of diquat absorbed by aquatic plants have not been determined as frequently as 43 have levels in water and hydros oil. In the southeastern U.S.A., Grzenda, Nicholson, and Cox (66) demonstrated rapid dissipation of diquat from water when applied at 2.5 ppmw. In a vegetation-free pond, diquat was not detectable after 30 days whereas in a plant-infested pond, disapperance had occurred within 14 days.Temperature differences did not affect dissipation rate. No desorption of diquat from the hydrosoil was detected (122). In concrete-lined, soil bottom ponds, Gilderhus (65) applied 1.0 ppmw diquat to infestations of E. canadensis.Ten days after treatment, 0.16 and 0.13 ppmw diquat was detected in the respective ponds. No diquat could be measured at the next sampling date, 30 days after treatment.Levels of diquat in the soil were 6.0 and 10.0 ppmw at 24 weeks after treatment. In 14 plant-filled California reservoirs (186), rates of diquat from 0.125 to 1.0 ppmw had dissipated to a level below 0.06 ppmw by four days after treatment and to 0.009 ppmw by 12 days.Frank and Comes (58) treated a Colorado farm pond with 0.62 ppmw diquat and observed dissipation rates of 0.49 ppmw at day one, 0.12 ppmw at day two,and 0.01 ppmw at day four. No diquat was detected at eight days.Levels of diquat in the hydrosoil had risen to 20 ppmw after 24 days.Diquat was still present at above 20 ppmw 160 days after treatment.It was concluded that the increase in diquat levels in the soil resulted from release of diquat from decomposing plants.Loss 44 of diquat between the time of absorption by vascular hydrophytes and decay of these plants is unlikely since Smith (148) and Funderburk and

Lawrence (62) observed no degradation of diquat in plant tissue.In static water canals in Florida, Mackenzie (103) reported that, after treatment of a 30% infestation of H. verticillata with 0.5 ppmw diquat, the diquat concentration had, by 14 days, dropped to 0.09 ppmw. No diquat could be detected at 21 days.In a comparable canal with 70% infestation, a 0.08 ppmw level was reached in eight days and no diquat was detected at 14 days following application.In the hydros oil, at the final three week sampling date, diquat levels reached 3.98 ppmw in the 30% canal and 3.13 ppmw in the 70% canal. In summary, diquat concentrations following application of 0.5 to 1.0 ppmw cation dissipate below detectable levels within 14 to 21 days.Soil residues are persistent.Faust and Zarins (52) noted the rapid absorption of diquat to bentonite clay in an aquatic environment. A rise in temperature from 10 to 20 C did not influence absorption rates. As indicated by their persistence in hydrosoil, diquat residues are biologically unavailable once absorbed to hydrosoil.This agrees with the terrestrial studies ( 1) which indicate absence of activity and slow breakdown of diquat in soils moderate in clay minerals and organic matter. 45 Effects on Aquatic Fauna and Microflora

Diquat has an acute oral LD50 to rats to 400 to 440 mg/kg (178) and is thus considered a moderately toxic herbicide. Swann (166) has demonstrated, in connection with aquatic applications of diquat, that a cow would have to drink 1500 liters of water treated with 0.5 ppmw diquat within 24 hours to receive a lethal dose. Lawrence, Beasley and Funderburk (96) could not detect drastic changes in water chemistry following treatment of plant-filled ponds with 0.25 to 0.5 ppmw diquat. Newman (120) noted that, in order to maintain dissolved oxygen levels above 8.0 ppm, diquat applications to densely infested ponds should be spaced 12 days apart. Reduced dissolved oxygen levels can occur when large quantities of vascular hydrophytes decay following herbicide application.

Fishes

Direct toxicity to fishes from diquat has not been observed at rates of 0.125 to 1.0 ppmw (23, 26, 27, 34, 58, 65, 90, 103, 121, 135, 140, 175, 186). Acute toxicity of diquat to many fish species have been determined in the laboratory.Bond, Lewis, and Fryer (29) found that the

Median Tolerance Limit for 48 hours exposure, TLm48 hours, was 14.0 ppm cation for Oncorhynchus tsawytscha, (Walbaum), Chinook 46 salmon, and 35.0 ppm cation for Salmo gairdneri, rainbow trout. Surber and Pickering (157) determined TL96 hours for Pimphales promelas, fathead minnows, to be 7.0 ppm and for Micropterus salmoides, largemouth bass, to be 4.0 ppm.In hard water the TL 96 hours for fathead minnows was 6.50 ppm.Bluegills treated by Hughes and Davis (86) for susceptibility to diquat, showed a TLm 48 hours of 125 ppm. Work in the Federal Fish-Pesticide Laboratory in Denver (37) reported that Effective Concentrations to cause 50% mortality, EC50 were 20 ppm for rainbow trout and 19 ppm for bluegills.Oncorhynchus kisutch (Walbaum), coho salmon and blugills were tested by Kibby (93) for susceptibility to diquat and TLm 96 hours values of 22.7 ppm and 20.7 ppm were reported.Gilderhus (65) documented Lethal Concentrations to cause 50% mortality, LC50' for bluegills at 35 ppm, Carassius auratus, goldfish at 35 ppm, Esox lucius, northern pike, at 16 ppm, rainbow trout at 11.2 ppm, and Stizostedion vitreum vitreum, walleye pike, at 2.1 ppm. Immature stages of fish have been tested for response to diquat. Eady and Renny (49) used eggs of Salvelinus fontinalis, eastern brook trout, in tests with different diquat concentrations.Survival of eggs exposed to 2.0 ppm diquat for eight hours was 88% compared to an untreated control survival of 91%.Hiltibran (79) exposed fertilized eggs and fry of bluegills to diquat; 10 ppm diquat did not cause loss of eggs or fry.These data suggested that, under field conditions, no 47 effect would be expected on survival of fishes' offspring.Gilderhus (65) noted that survival of fingerling bluegills was equally good in all pools,whether control or treated with one and three ppmw diquat. It was also observed that no haematological or histopathological effects were found in these fish. Levels of diquat found in fish exposed to diquat have been measured.Bluegills exposed to one ppmw diquat in Wisconsin (65) had body levels of 0.09 to 0.16 ppmw at three weeks, 0.03 to 0.06 ppmw at six weeks and no detectable diquat at 12 weeks after treatment. Studies with goldfish (11) showed that maximum diquat activity was in the gut after exposure to four ppmw diquat. Removal of14C diquat was achieved by allowing the fishes to swim in fresh water for ten days.Trace amounts were found in the gut.In England (120), rainbow trout exposed to one mg/1 diquat for 11 days had a whole body level of 0.36 mg/kg diquat. No diquat could be detected in the muscle tissue.

Aquatic Invertebrates

Aquatic invertebrates make up a large portion of the diet of many fishes (117).Toxic effects on these organisms could have serious consequences for fishery resources dependent upon them. Indirect effects of herbicide application on invertebrate populations can result from removal of habitat (75). 48 In the laboratory, Wilson (185) determined TLm 96 hours values of 16 mg/1 diquat for the immature stages of certain important invertebrates such as Libellula sp., dragon fly naiads, Coenagrioni- dae sp., damsel fly naiads, Baetidae, mayfly nymphs, Tendipididae larvae, and Limnephilidae, Caddisfly larvae.Hyallela sp., an amphipod adult, was found to have a TLm 96 hours value of 0.048 mg/1 diquat. When soil was added to the test vessel, the TLmvalue rose to 6.8 mg/1 for 96 hours exposure.In England, Alabaster (2) noted that TLmhour values for Tubifex sp., Daphnia sp., Asellus sp., and Gammarus sp. were two or more times higher than for Rasbora hetermorpha, harlequin fish. The microcrustacean, Daphnia sp., a Cladoceran, forms a significant portion of the food source for immature and adult fish in temperate climates.Crosby and Tucker (42) reported Immobility Concentration of 50% of the population at 26 hours, IC50 26 hours, of 7.1 ppm for diquat.Gilderhus (65) noticed reduction of Daphnia sp. in the field after a diquat application of one ppmw.In laboratory studies, one ppmw diquat delayed development of immature forms of Daphnia pulex while three ppmw diquat killed the test population. Field studies in invertebrate populations have been conducted. Data presented below represents "standing crop" of the organism sampled. Tatum and Blackburn (161) applied 0.5 ppmw diquat to two Florida farm ponds and found bottom organisms numbers unaltered 49 by the treatments.Composition of the population was, however, altered temporarily.In Missouri (182), a two ppmw diquat treatment demonstrated no toxic effects to bottom fauna such as

Tendipidid larvae,Oligochaetes, and Libellulid nymphs.In 1964, diquat applied at rates from 0.25 to 0.76 ppmw to experimental ponds, did not reduce numbers of benthic organisms.Hilsenhoff (75) applied 1.0 ppm diquat to a pond infested with E. canadensis and observed no direct effects of diquat to the aquatic insect population.Benthic organisms were not disturbed by the treatment. Newman (120) recorded no detectable effects on bottom organisms when diquat was applied at one ppmw. Dutch research (23) showed that seasonal changes in members of Cladocerans, Copepods, and Rotifers were not altered after treatment with 0.4 to 0.8 ppmw diquat. No acute toxicity was reported.In Wisconsin, Gilderhus (65) noted that control ponds had fewer invertebrates than ponds treated with diquat. Dense vegetative bottom cover provided by uncontrolled growth of E. canadensis reduced midge larval population.Diquat at one and three ppmw did not reduce numbers of the Cladoceran, Daphnia pulex, in this study.In experimental ponds, Wilson (185) reported reduction in amphipod numbers when diquat was applied for E. densa control at 2.5 ppmw. Populations of invertebrates such as Tendipids and Libellulids were not effected. 50 Phytoplankton

Phytoplankton represent the producer organisms in the first or foundation trophic level of the aquatic system.Field studies in Florida (161), Missouri (182), and Holland (23) indicate that application of 0.5 to 2 ppmw diquat did not effect phytoplankton populations. Nor- mal seasonal fluctuations were observed.In contrast, a laboratory study conducted by U.S. D.I. (166) demonstrated that exposure to 1.0 ppm diquat for four hours reduced the production of a natural phytoplankton population by 45%. In summary, diquat possesses a wide margin of safety to warm and cold water fish species.The lowest TLm value recorded is 2.1 ppm for walleye pike and the highest, 125 ppm for bluegills. No direct toxicity has been observed in field trials.Diquat does not affect fish- food organisms at rates applied for vascular plant control. Amphi- pods and Cladocerans are more sensitive to diquat at 2.5 and 3 ppmw treatment rates than other invertebrates.

Disodium Endothall

Disodium endothall, the disodium salt of 7-oxabicyclo (2.2.1) heptane -2, 3- dicarboxylic acid, is a contact aquatic herbicide (Figure

2).Development of endothall compounds has been conducted by Pennwalt Chemical Corporation, Tacoma, Washington (91). 51 Physical and Chemical Properties

Endothall acid is a crystalline, white solid with a solubility of 10 grams per 100 grams of water (91).The disodium salt is available as a 19.2% aqueous solution.

Mode of Action, Uptake, and Effect of Environmental Factors on Activity

Endothall exerts its phytotoxicity by disintegration of the lipo- protein complex of membranes (91).In addition, endothall has been reported to induce callose formation in parenchyma, epidermal, and mesophyll cells.Abnormal permeability followed by loss of water and tissue dessication then occurs. In aquatic plants, Seaman and Thomas (145) utilized excised leaves from P. nodosus and P. pectinatus and trifoliate nodes from E. canadensis to detect uptake of disodium endothall.The pondweeds absorbed more than twice as much endothall from a 0.1 ppm solution as did E. canadensis.Endothall uptake was reduced 95% when these submersed aquatic plants were pretreated with respiratory inhibitors such as KCN. Thomas (162) reported that trans location of endothall occurred in P. nodosus from leaves to other portions of the plant while none was observed with E. canadensis. Studies on the effects of environmental factors on endothall activity are limited.Walker (173) reported that water temperature 52 should exceed 15 C to obtain control with endothall.Yeo (187) noted that control of susceptible plants in the field was complete in eight to 12 days when water temperatures were 20 to 25 C. A water temperature of 16.5 C resulted in slower activity from a single disodium application.Instructions for use of sodium endothall recommend that water temperatures be above 19 C for optimum effectiveness of the herbicide (130).

Hydrophyte Control

Disodium endothall has been widely used in the United States for submersed aquatic plant control.Hiltibran (77) and others (173, 187) reported that it was effective for control of Potamogeton sp.

Elodea densa Planch.

Disodium endothall does not control E. densa at 25 ppmw (26). Other salts of endothall such as the dimethylcocoamine formulation however, have been extremely effective at rates as low as one ppm both in the laboratory (14, 91) and in the field (15).

Elodea canadensis Michx.

Disodium endothall does not control E. canadensis at 10 ppmw (77, 145, 187).Walker (173) did report some control in small plants with one to three ppm disodium endothall; however, regrowth 53 occurred. Seaman and Thomas (145) observed that uptake of dimethylalka- mine endothall, toxic to E. canadensis was absorbed by that plant in lesser quantities than disodium endothall.The lack of control of E. canadensis did not appear to be due to lack of endothall in the treated plant.

Ceratophyllum demersum L. and Myriophyllum sp.

Yeo (187) reported control of C. demersum with 0.35 to 1.9 ppm applications of disodium endothall.Water temperatures were 20 to 25 C.In Illinois, Hiltibran (77) observed severe damage to C. demersum and M. exalbescens from 5.0 ppm disodium endothall treatments.In Wisconsin (173), rates of one to three ppm disodium endothall gave consistent control of C. demersum and M. heterophyl- lum.

Persistence in Aquatic Environment

Endothall is considered to be readily biodegradable by aquatic plants, fungi, and bacteria.Evidence in support of this statement has been reviewed by Keckemet (91).Breakdown products can be utilized in the metabolic processes of exposed organisms.Hiltibran (76) showed that a 1.0 ppmw treatment of disodium endothall was reduced to below 0.4 ppm within 24 hours after application.It took ten 54 days for a five ppm treatment to be reduced to this level.Yeo (187) treated 14 California reservoirs with rates of 0.25 up to 3.0 ppmw disodium endothall.Within 12 days, 71% of the applied endothall was lost.Results were very inconsistent.In eight out of 14 reservoirs, little dissipation occurred between the fourth and twelfth day after treatment; however, where water temperatures exceeded 20 C, the rate of dissipation increased.The presence of a thermocline resulted in concentration of endothall above that layer. Absence of a sensitive analytical technique for endothall residues in other organisms has delayed further experimentation (91).

Effect on Fauna and Microflora

Disodium endothall has an oral LDof 198 mg/kg for rats (91) 50 and is considered a moderately toxic herbicide.Endothall fed to rats was completely eliminated from all tissues and organs in 72 hours.

Fishes

Disodium endothall was widely tested against many species of fish.Surber and Pickering (157) reported TL96 hours values of 180 ppm for bluegills, 320 ppm for fathead minnows, and 200 ppm for largemouth bass in soft water.Hughes and Davis (85) recorded a TLm 96 hours value of 200 ppm for bluegills with disodium endothall. Nine species in the minnow, catfish, and sunfish families had TL 55 96 hours values of 60 to 120 ppm (173).Disodium endothall had no effect on the fertilized eggs and fry of bluegill (79).Hiltibran felt that, "Endothall, because of its low toxicity to fish, low toxicity to eggs or fry and rates of aquatic use, appears to be one of the safest herbicides to use during the spawning season".Studies by Freed (131) indicated that goldfish were able to metabolize endothall.

Invertebrates and. Phytoplankton

Virtually no information is available on the effect of disodium endothall on benthic organisms, phytoplankton or other important items on the food chain.The slight amount of information is reassur- ing.Walker (172) studied 270 tests involving application of disodium and dimethylcocoamine endothall and found no obvious effect on bottom fauna at rates from one to three ppmw. An indirect increase in numbers of organisms due to nutrient release in successfully treated ponds was recorded. Crosby and Tucker (42) required 36 ppm endothall before 50% of a Daphnia magna population was immobilized.

Copper Sulfate

Copper sulfate, CuSO4, 5H20,is a contact algicide and aquatic herbicide (Figure 2).No reviews on its activity towards vascular hydrophytes are available. 56 Physical and Chemical Properties

Copper sulfate pentahydrate is soluble in water.Solubility (102) is determined by pH, alkalinity, and temperature.In alkaline aqueous solutions (100), copper will be precipitated by hydroxide and carbonate ions.

Mode of Action, Uptake, and Effect of Environmental Factors on Activity

The mode of action of copper sulfate on submersed hydrophytes has not been studied.It is probable that accumulation of copper ion in the plant causes defoliation and eventual collapse.Uptake of copper sulfate by aquatic plants has been reported by Bartley (10).Stimula- tory effects at low levels of copper sulfate have been recorded (177). Hale (67) noted a temperature effect on copper sulfate phytotoxicity; dosage rates had to be doubled in winter applications to achieve algae control.This is possible associated to lower solubility of copper as is suggested by Mackenthun and Ingram (102). McKee and Wolf (100) noted that amounts of copper sulfate required for algae control should be increased by 2. 5% for each degree that water temperature fell below 15 C.

Hydrophyte Control

Copper sulfate at one ppmw will control most problem algae (67, 57 100, 102, 107) while control of vascular hydrophytes is not achieved at this rate of application.Higher rates of application are required for vascular plant control. Under Oregon conditions, E. densa was treated with rates of copper sulfate which ranged from 3.5 to 30 ppmw. The optimum rate for control was 10 ppmw. Bond (25) and Kerns (92) reported 75% control from 10 ppmw applications as opposed to 100% control from 40 ppmw. Saltzman (138) demonstrated good "knockdown" with a 5 ppmw rate of copper sulfate and boat channels were subsequently cleared using this treatment on Tahkenitch Lake.In Florida (175), 4.5 ppmw copper sulfate gave 50% control and nine ppmw gave 100% control of E. densa infestations in Lake Thonosasso.

Persistence in the Aquatic Environment

Upon application of copper sulfate to the aquatic environment, concentrations of copper build up in the hydrosoil (102).Studies in Wisconsin Lakes (100) documented maximum levels of 438 mg copper/ kg of soil after 26 years of copper sulfate application.The total amount of copper salts applied to the lakes studied was over two million pounds.

Effects on Fauna and Microflora

Various writers (40, 70, 71, 177) have condemned the continuous 58 use of copper sulfate for algal and plant control.Pitney (132) stated that copper sulfate "has a sterilizing effectupon bottom muds, killing most of the animal and plant life and producingtemporary biological deserts in areas which have received heavyor repeated treatments".

Fishes

Copper sulfate is recognized as harmful to fish.Concentrations of copper sulfate tolerated by fishes in mg/1copper sulfate were 0.14 for trout, 0.33 for sucker andcarp, 0.40 for catfish and pickerel, 0.5 for goldfish, 0.67 for perch, 0.8 for baseand bluegill, and 1.35 for sunfish (100). Work with rainbowtrout and bluegills (37) showed that they had EC50 values of 0.15 and 2.5ppm respectively upon exposure to copper sulfate.Fish were more resistant tocopper sulfate in hard, alkaline water than soft, acid water.Meyer (111) reported that largemouth bass tolerated 3.0ppmw in a treated pond. Bond (25) felt that 2.0 to 5.0 ppmw applicationswere dangerous to salmonid fish in Oregon. Under field conditions, expressionof toxicity to fishes from copper sulfate is moderated by environmentalfactors.In Florida (175) no fishes were distressed bya treatment of nine ppmw copper sulfate at pH 7.3 and 63 ppm CaCO3.

Invertebrates

Chironomus sp., bloodworm larvae, were unharmed by100 59 mg/1 copper sulfate (100) while Daphniamagna has been killed by 0.01 mg/1 copper sulfate.Simulium sp., gnat larvae, were unaffect- ed by 10 mg/1 copper sulfate.Hale (37) reported that Cyclops sp. and Daphnia sp. could be controlled by 2.0 ppmw treatment rates. In field situations, Saltzman (139) reported a reduction in numbers of benthos around dock areas repeatedly treated with copper sulfate.Walker (172) noted similar decreases in the northcentral states.Mackenthun and Ingram (102), however, did not find levels of copper in bottom muds which were as high as those necessary to pro- duce toxic effects on benthos under laboratory conditions.

Phytoplankton

As an algicide, copper sulfate has a very definite effect on phytoplankton (67, 100).Diatoms and green algae are controlled by rates from 0.12 to 0.5 ppmw copper sulfate while bluegreen algae are sometimes resistant to copper sulfate treatments. Aphanizomenon sp. were regarded (102) as having aquired a certain tolerance to continued applications.Rates of copper sulfate required for vascular plant control have a severe effect on existing phytoplankton populations.

Dichlobenil

Dichlobenil, 2, 6-dichlorobenzonitrile, is a soil-acting aquatic 60 herbicide (Figure 2).It was discovered and developed by N. V. Philips Duphar, Amsterdam, Holland.

Physical and Chemical Properties

Dichlobenil is a white crystalline solid and is relatively volatile

(178).Water solubility is 18 ppm at 20 C while solubility in organic solvents is moderate. When suspended with water, or when exposed to ultraviolet light or sunshine, dichlobenil does not degrade.

Mode of Action, Uptake, and Effects of Environmental Factors on Activity

Dichlobenil inhibits seed germination and actively dividing meri- stems, such as growing points and root tips,It is strongly absorbed by the epidermis of shoots. Growth of emerging sprouts of perennial terrestrial plants such as Equisetum sp. and Agropyron sp. has been prevented by dichlobenil (178).Dichlobenil is mainly absorbed from the soil via the root system. Studies in terrestrial plants revealed some movement from roots to shoots but negligible downward movement. Uptake of dichlobenil by submersed, nonvascular aquatic plants has been measured (38).An infestation of the alga , Chara sp. was treated with ten pounds per acre dichlobenil in a Colorado farm pond. Dichlobenil was rapidly absorbed by Chara sp. within six hours of treatment; levels in ppm dichlobenil were 44 at six hours, 60 at one 61 day, 77 at two days, 49 at four days, 21 at eight days, and 5 at 16 days.After 16 days no plants remained for sampling. Spirogyra sp.,

a filamentous green alga ,has accumulated 404 ppm dichlobenil six hours after treatment. By four days, levels in the algae had dropped to 16 ppm. Growth of Spirogyra was retarded but regrowth commenced three months after treatment when the levels of dichlobenil in the plant were 0.7 ppm.

Hydrophyte Control

Dichlobenil, as a 4% sinking granule, is most effective when applied to bare soil prior to flooding of the water prior to plant emergence in the spring.Post-emergence foliar applications have been less successful (38). In Wisconsin (174), 16 out of 22 pre-flooding applications of 20 to 40 pounds dichlobenil per acre gave successful plant control.Pre- emergence applications to the water were only successful six out of 24 times.Control of Potomogeton sp. and Najas sp. was about 50% with the 20 pound rate while 75 to 90% control was obtained with the 40 pound rate.In Colorado (38) a ten pound per acre application to the water gave excellent control of Chara sp., Potamogeton sp. ,and C. demersum. In Florida (176), 101 pounds per acre gave no control of an E. densa infestation while application of seven and 15 pounds per acre 62 gave no control when applied to E. densa infestations in Oregon (27,

90).In Holland, van Busschbach and Elings (168) used a 3.0 ppmw rate to obtain excellent post-emergentcontrol of E. canadensis.

Persistence in Aquatic Environment

In Oklahoma (38), 10, 20, and 40 ppmw dichlobenil were applied to experimental ponds devoid of vegetation. No dichlobenil would be detected in any of these ponds at 85 days after treatment.At 10 ppmw, dichlobenil levels had reached 80 ppmw by three days but fell to 0.03 ppmw by 40 days.At 40 ppmw, 130 ppmw dichlobenil were detected at three days.Sixty-three days after treatment, a 0.04 ppmw level was reached.In Colorado (58, 111), two ponds were treated with 0.4 and 0.58 ppmw dichlobenil.The highest detectable level in either pond was 0.32 ppmw at three days.However, as a more sensitive analytical technique was used, 0.0004 ppmw dichlobenil was found in the 0.58 ppmw pond at 160 days after treatment. In another Colorado pond (38, 171), 0.6 ppmw dichlobenil persisted up to 188 days.Depth of water in the various ponds did not affect dissipation rates. Persistence of dichlobenil was observed in hydrosoils in Colorado (58, 111) and Oklahoma (38).At the 10, 20, and 40 ppmw levels, dichlobenil residues peaked at 46 to 60 days after treatment. By 312 days, dichlobenil residues in all ponds ranged from 0.028 to 63 0.075 ppmw. When lower rates of dichlobenil, 0.4 and 0.58 ppmw, were applied in Colorado the optimum dichlobenil concentration was detected one to two days after treatment. By 160 days after application no dichlobenil could be detected in the 0.58 ppmw pond whereas 0.12 ppmw was found in the other pond. Persistence of dichlobenil is necessary for effective suppression of vascular plant regrowth.It can be observed that variation in persistence of dichlobenil occurs at normal treatment rates as was demonstrated in the Colorado trials (8, 111).

Effect on Fauna and Microflora

The acute oral toxicity of dichlobenil to rats has been established as LD 3160 mg/kg (178). 50

Fishes

Acute toxicity studies on bluegills (86) with dichlobenil granules resulted in a TL48 hours of 37 ppm. Walker reported (174) TLm 96 hours of 20 ppmw for bluegills and 10 ppmw for largemouth bass. Determinations with bluegills (167) gave LC50 96 hours of 10 ppmw and LC50 48 hours of 20 ppmw. The corresponding data for rainbow trout were 18 and 22 ppmw (37, 167).Hiltibran (79) declared dichlobenil to be a safe material when applied to fertilized eggs and fry of bluegills. 64 In field studies (38), reproduction of bluegills was affected by a 40 ppmw treatment but not by 10 and 20 ppmw treatments. No immediate mortalities were observed in these studies. Fish exposed to dichlobenil in Oklahoma (38) and Colorado (58, 171) both absorbed the herbicide.In Oklahoma, high levels of 24 to 128 ppmw in bluegills, recorded at three days after treatment, were reduced to one and two ppmw by 18 days after treatment.At 11 days

0.137 to 0.92 ppmw dichlobenil was detected in whole fish.At Denver, levels were lower and developed more slowly on whole fish. Four different species of fish were analyzed for dichlobenil residues. In bass, the high 4.25 ppmw level was reached by 34 days and reduced to 0.04 by 189 days.In bluegills, the high level was reached at 16 days and remained at 7.9 ppmw until 34 days had elapsed. By 189 days, the levels of dichlobenil were 0.03 ppmw. Peaking of residues in fish occurred slightly later than that peak which occurred in the water samples. Small quantities of degradation product, 2, 6-dichlorobenzoic acid have been found in some crops (178).It is not known if this occurs in submersed aquatic plants.

Invertebrates and Phytoplankton

Various aquatic invertebrates were exposed to dichlobenil by Wilson (185).In most cases, a narcotizing effect on these animals 65 was produced before demonstration of toxicity.Narcotization, as measured by Immobilization Concentration for 50% of the test population, IC50, was 2.8 mg/1 dichlobenil for Hyallela sp., an amphipod. The TL96 hours for Hyallela sp. was 8.5 mg/l. Acute toxicity to other invertebrates as measured by TLm 96 hours in mg/1 dichlobenil was greater than 100 for dragonfly naiads, 20 for damselfly naiads, 10 for mayfly nymphs, 8 for Tendipid larvae, and 13 for caddisfly larvae.In another study (167), Pteronarcys california, stonefly, had an LC50 96 hours of 6.6 mg/l.In experimental ponds, Wilson (185) demonstrated reductions in numbers of Tendipidids but not of Hyallela sp. or Libellulids. No effects of dichlobenil have been recorded on phytoplankton. Observations in the field (38) indicated that there were no acute effects of dichlobenil on filamentous algae. On the other hand, Wilson (185) reported complete suppression of filamentous algae in Oregon ponds. 66

VII.Herbicide Combinations in Aquatic Weed Control

Herbicide mixtures have not been commonly used in aquatic weed control.The exception is the combination of potassium endothall and silvex manufactured by Pennwalt Chemical Corporation, Tacoma, Washington (130).This combination of dipotassium endothall with potassium salt of silvex (178) is utilized to control emergent and submersed plants. Combinations of herbicides for control of submersed aquatic plants could be made for two reasons.The first reason would be the convenience of a broad-spectrum herbicide.The second reason would be the possibility of improved control of a hard-to-kill plant.Syner- gism can be defined as that response over and above strictly additive effects observed when one herbicide is combined with another.Colby (37) developed an equation which gave the expected degree of control of a herbicide combination based upon additive effects of two or more herbicides whose effectiveness singly had previously been determined. Any increase or decrease in control from the calculated effect can be labelled "synergism" or "antagonism". Because individual effectiveness ratings are not always available for the individual components of a mixture, such calculations are not always possible. Limited studies with bipyridyl herbicides were summarized by Akhavein and Linscott (1).Pretreatment of Paspalum conjugatum 67 with 3-amino-1, 2, 4-triazole plus ammonium thiocyanote (73) enabled control to be obtained by a follow-up treatment with paraquat.If applied as a mixture, the effect was antagonistic. Bovey and Miller (31) demonstrated that the effectiveness of paraquat as a sorghum dessicant was increased by addition of dimethylalkyamine endothall. In aquatic situations in Florida, Mackenzie and Hall (103, 104) showed that diquat at 0.5 ppmw plus copper sulfate at 2.0 ppmw gave excellent control of H. verticillata in situations where either treatment alone would have been ineffective.Blackburn and Weldon (19) applied endothall and copper sulfate alone and in combination with diquat and found that addition of copper sulfate at one ppmw to 0.25 ppmw diquat increased control of H. verticillata at six weeks from 45 to 80%.At this date one ppmw copper sulfate gave 10% control.Using the equation of Colby (37), an expected control figure at six weeks would be

50. 5 %.The observed response from diquat plus copper sulfate is synergistic.Combinations of higher rates of copper sulfate (19) with diquat resulted in more rapid control but gave no greater overall control of H. verticillata.Application of 0.5 ppmw diquat did not give control equal to that achieved by 0.25 ppmw diquat plus 1.0 ppmw copper sulfate.In the field, rates of two ppmw diquat or 80 ppmw copper sulfate alone were required to obtain control of H. verticillata. Control was improved by application of one ppmw diquat plus four ppmw copper sulfate.Use of the Colby equation (37) results in an 68 expected additive effect of 78% control at four weeks. The 100% control obtained with the combination at four weeks represents a synergistic effect. A tank mix of diquat and copper sulfate was a more effective means of combination application than application of the two compounds separately (19).The addition of diquat to copper sulfate does not result in formation of a new molecule (46). Endothall has been applied to diquat in laboratory (19) and field (39) studies.Control of H. verticillata with diquat was not enhanced by addition of equal rates of endothall.Diquat at 0.5 ppmw alone gave 80% control whereas 75% control resulted from a 0.5 ppmw combination of both herbicides.In Virginia, Corning and Prosser (39) claimed that diquat plus endothall exerted synergistic effect on control of E. densa.Diquat at 0.23 ppmw and dipotassium endothall at 0.17 ppmw were applied as a mixture to 200 acres of E. densa.Diquat was also applied alone to 16 acres of E. densa at 0.45 ppmw. Both treatments gave 100% control. No treatment of 0.23 ppmw diquat was made for comparative purposes. No toxicity to warm water fishes was observed. No laboratory studies have been reported on the effect of diquat combination treatments on E. densa with either copper sulfate or endothall. 69 VIII.Recreational Values and Economic Justification for Aquatic Plant Control Programs

The E. densa problem has existed in Oregon lakes since 1946. Research has been conducted over the past 25 years in an effort to solve this problem. Saltzman has noted that no contingency plan exists to employ the results of research success to the problem of the coastal lakes (138).No information is available on the value of these lakes to the local or state economy (139) nor is there a means by which a control program could be financed (138).Anglers have been observed to turn away from the plant-infested boat landings on Tahkenitch Lake (137).These questions are important in that the role of aquatic plant management in recreational resource management has yet to be defined. Natural resource management has had application of planning and economic analysis in recent years (74, 153).Benefits to local and national economies, deriving directly from recreational resources such as sport fishery, have grown to major significance (74).Al- though inherent aesthetic values are difficult to measure, expenditures on recreational fishing in the U.S.A. accounted for three billion dollars in 1965.This was spent by 33% of the U. S. population over 12 years of age. Pressure on existing recreational areas will increase greatly in the U.S.A. There is no "New Frontier" into which to expand in the 1970's.Discretionary spending increased by 44% 70 from 1949 to 1966.Discretionary leisure time averaged 125 days per annum per individual (74).These pressures on recreational resources demand a philosophy which emphasizes:

a) continual inventory of resources

b) planned development and cooperation

c) consideration of the TOTAL environment

d) continual improvement of resources suceptible to improvement

e) optimum multiple use of resources. There is no evidence to show that excessive plant growth in recreational fishing resources have been subject to such philosophical considerations or to economic analysis.Quantitative values have not been derived for plant control programs. Biological information is lacking to aid in economic analysis. Limited studies have been made on the recreational benefits of water pollution control and improvement of water quality.Stevens (154) recognized the difficulties inherent in placing economic value on sport fishing and noted that preferences not expressed in market activity are difficult to evaluate and quantify. Normal market mecha- nisms are often inoperative since many sport fishing facilities are publicly owned (152).Outdoor recreation, in general, has tradi- tionally been characterized by free or low costs (153).Results from a study (152) conducted on the fisheries of Yaquina Bay, Oregon, 71 showed that angling success was rewarded by an increase in angler effort.This held true for salmon fishing.However, angling for bottom fishes in the estuary was less responsive to changes in success.If water pollution was assumed to inhibit success at catching salmon, then there would be a decrease in angler effort with a con- commitant reduction of expenditure on angler visits to the fishing region. The use of demand equations to calculate possible economic benefits or detriments resulting from pollution control was thought to be feasible (153).It was stressed that quantitative biological information was necessary to enable the economist to derive such equations. Gibbs (64) utilized recreational demand curves to estimate economic benefits to local society resulting from an improvement on water quality in Upper Klamath Lake, Oregon. The willingness of recrea- tionists to pay more to arrive at an improved site and then stay there longer once arrived was estimated.Values could then be placed on the economic benefits accruing from control of bluegreen algae, from lowering of water temperature and improvement of beach facilities. Gibbs estimated that an increase of $4, 000, 000 per annum in tourist income would accrue to the local economy if bluegreen algae ceased to present a problem in Upper Klamath Lake. It was felt (153) that methodology developed in these studies could be extended to evaluation of relative efficiency of public 72 investments in fish hatchery facilities, predator control and habitat improvement. Measures to increase angler success could be evalu- ated. Such studies have not been projected for analysis of aquatic plant management programs in recreational lakes. 73 MATERIALS, METHODS, AND RESULTS

Laboratory Trials

In the laboratory studies, the objectives were to investigate the effectiveness of diquat and diquat combinations for control of submersed aquatic plants with emphasis on E. densa and to determine the effect of time of application, exposure time, light quality, and water temperature on the activity of diquat and diquat combinations against E. densa. All laboratory trials were conducted at Fairplay Laboratory, near Corvallis, Oregon from July 1969 to May 1970.Plants utilized were E. densa, E. canadensis, C. demersum, and M. verticillatum. These submersed plants were harvested from Siltcoos Lake and stored in lighted, aerated, 760-liter, black plastic tanks at water temperatures to 14 to 18 C. All experiments were conducted in large water baths with continuous water circulation at a thermostatically controlled temperature. Three-liter glass jars which contained three liters of water from a nearby deep well were used as individual plots.Water quality was monitored by the U. S. Geological Survey over a 12 month period (Appendix Table 1).Four apical segments of E. densa, 100 cm in total length and 15 gm fresh weight, were placed in two white, two- inch square plastic pots which were then filled with washed, 30 mesh 74 white sand. Each jar, containing four plant segments, was allowed to equilibrate in the water baths at the experimental temperature for ten days prior to herbicide application. Plants were grown under a 12 hour light,12 hour dark photoperiod.Water temperatures were adjusted by electric water heaters and a dairy water cooler.Each jar was aerated regularly (Plate 3). Herbicides were applied by pipette directly to the jars from stock solutions of diquat, disodium endothall, and copper sulfate pentahydrate on a part per million by weight basis.Application was made after six hours of the light period had elapsed.Combination treatments were applied by separate administration of the constituent herbicides. All results were recorded on the basis of visual estimation of control, on a percentage basis, on length of plant stem remaining viable, and dry weight of this material.Visual estimation of control reflects a personal assessment of disintegration of stem and leaves. Complete 100% control of E. densa was recorded when the plants were controlled to the sand surface whereas zero percent control was recorded when no effects were visible (Plate 4).

Preliminary Screening Trial

The purpose of this experiment was to evaluate the effectiveness of diquat alone and in combination with copper sulfate and endothall 75

Plate 3.Typical plot in Preliminary Screening Trial, Fairplay Laboratory, 1969.

Plate 4.Control of Elodea densa with diquat at 0.5 ppmw. Control plot on right. 76 for control of submersed aquatic plants, E. densa, E. canadensis, C. demersum, and M. verticillatum found in Siltcoos Lake, Oregon.

Materials and Methods

The trial was conducted in two wooden water baths (Plate 5). Two overhead, eight-foot long, Sylvania Cool White (Daylight) 40 watt lamps supplied light.The light intensity was measured at 1660 lux at

the water surface by a Weston Illumination Meter, Model 756.The water bath units were covered completely by black polyethylene to

exclude external light.Water temperature was 20 C ± 0.5 C.Diquat was applied alone at concentrations from 0.1 to 1.0 ppmw and in combination with 0.5 ppmw copper sulfate and 0.1 and 1.0 ppmw endothall.Herbicide treatments were replicated two times.

Results

Diquat at rates to 0.25 to 1.0 ppmw alone or in combination with endothall and copper sulfate controlled the exotic hydrophyte, E.

densa (Appendix Tables 2,3,4).In addition, E. canadensis, C. demersum, and M. verticillatum were controlled effectively by 0.25 to 1.0 ppmw diquat alone or in combination (Appendix Tables 2,3,4).

Time of Application

Optimum time of application for bipyridyl herbicides is Plate 5.Wooden water baths with experimental jars, Fairplay Laboratory, 1969.

Plate 6.Metal water baths showing arrangement of lamps and polyethylene screening, Fairplay Laboratory, 1969. 78 immediately prior to nightfall. No quantitative information supports this belief with regards to application of diquat for control of submersed hydrophytes.This trial was designed to test the hypothesis that the time of day at which diquat or diquat plus copper sulfate was applied to E. densa would affect the degree of plant control obtained.

Materials and Methods

Experimental methods were similar to the Preliminary Screen- ing Trial except that E. densa was the only test species.Diquat at 0.5 and 0.25 ppmw, 0.25 ppmw diquat plus 0.5 ppmw sulfate, and 0.5 ppmw copper sulfate were applied at four different times during the day; beginning of the 12 hour light period, middle to the light period, beginning of the 12 hour dark period, and middle to the dark period.Each treatment had four replications.The trial was harvested 21 days after herbicide application.Visual estimation of control, length of stem, and dry weight to stem were analyzed as a three- factor analysis of variance; the factors being time of application, chemical treatments, and replications.

Results

Application of diquat alone or in combination with copper sulfate controlled E. densa more effectively when applied at the beginning and the middle of the light period than when applied at the beginning or 79 Table 2.Effect of time of application of various chemical treatments on control of E.densa.-1/

Time of application ppmw Mean dry wt. Averagecontrol-2/ (mg) (%) Time of Application (All Chemical Treatments)

Beginning of 12 hour light period 611 67 Middle of 12 hour light period 663 67 Beginning of 12 hour dark period 776 47 Middle of 12 hour dark period 746 50

LSD = 85

(Control treatments 1461 Chemical Treatment (All Times of Application)

Diquat 0. 5 73 100 Diquat 0.25 270 92 Diquat + CuSO4 0.25+0.25 217 94 CuSO4 O. 5 1474 3 Control 146)--- 0

LSD = 96 O. 01

1Dataand statistical analysis in Appendix Tables 5,6,7, and 8. 2Visualestimate of control of E. densa. 80 the middle of the dark period (Table 2). Diquat at 0.5 ppmw gave superior control of E. densa under these conditions than did diquat at 0.25 ppmw alone or in combination with 0.5 ppmw copper sulfate.Nevertheless, the 92% control achieved with 0.25 ppmw diquat is equivalent to acceptable field control of E. densa.

Time of Exposure

Length of exposure time to diquat does influence control of E. densa, but the influence of water temperature on diquat activity at different exposure times is unknown.This trial was designed to determine the optimum exposure time at 10, 20, and 30 C for diquat and diquat plus endothall as a control measure against E. densa.

Materials and Methods

Experimental methods were similar to those used in the Time of Application study.Water temperature was controlled at 10, 20, and 30 C + 0.5 C.Diquat at 0.25 ppmw and 0.25 ppmw diquat plus 0.25 ppmw endothall were applied to E. densa.After herbicidal treatment for 0, 2,6,12, 24, and 48 hours, and until harvest, exposed plants were transferred to jars containing untreated water. Harvest dates were 240 hours at 30 C, 500 hours at 20 C, and 720 hours at 10 C.Visual estimation of control, length of stem, and 81 dry weight of stem were analyzed as a three-factor analysis of variance; the factors being chemical treatment, exposure time, and replications.The experiments at 10, 20, and 30 C were analyzed separately.

Results

A decrease in water temperature from 30 C to 20 C to 10 C reduced the speed of diquat activity but not the effectiveness of E. densa control (Table 3).At 30 C, there was a slight advantage in E. densa control with the addition of 0.25 ppmw endothall to 0.25 ppmw diquat; the opposite was found at 10 C. As water temperature decreased from 30 C to 20 C to 10 C, longer exposure times to diquat alone or in combination with endothall were required for optimum control of E. densa.At 30 C, exposure time necessary for complete control was six hours.The minimum contact time, two hours, provided an average control of 86% by diquat and diquat plus endothall. When the water temperature was decreased to 20 or 10 C, a chemical exposure time of 24 hours reduced the dry weight of harvested E. densa to levels consistent with optimum control.At 20 C, exposure times of six hours or less resulted in less than 80% control of E. densa.At 10 C, exposure times of 12 hours or less were correspondingly less successful for complete control of E. densa.Control ratings of 80% and above indicatelittle 82

Table 3.Effect of time of exposure of two chemical treatments on control of E. densa..1/

Mean dry wt. (mg) Average control (421

10C 20C 30C 10C 20C 30C

Chemical treatment (All exposure times)

Diquat 0.25 ppmw 383 373 328 70 82 90 Diquat + endothall 0.25 + 0.25 ppmw 474 342 274 62 82 93

LSD NS NS NS 0.0 1 (Control treatments 1381 1414 1461 0 0 0)

Exposure time (Both chemical treatments)

0 hours 1381 1414 1461 0 0 0

2 hours 595 366 355 33 66 86 6 hours 440 267 142 68 78 99 12 hours 303 181 41 75 88 100 24 holm 120 102 43 92 99 100

48 hours 83 82 32 97 100 100 3/ Termination of experiment- 78 91 32 100 100 100

LSD 77 59 78 0.01

1/Data and statistical analyses in Appendix Tables 9 to 17. ?VisualVisual estimate of E. densa control. 3720 hours for 10 C, 500 hours for 20 C, and 240 hours for 30 C. 83 capacity for immediate regrowth from the affected plants.

Light Quality and Water Temperature

The quality of light to which plants are exposed in the aquatic environment varies in addition to changes in water temperature.This trial was designed to determine the effect of variation in light quality on the activity of diquat alone and in combination with copper sulfate and endothall for control of E. densa at 10, 20, and 30 C.

Materials and Methods

This trial was conducted in a system of metal water baths (Plate 6).An individual lighting system was constructed for each of four baths by suspension of six-foot long, 40 watt, Sylvania Cool- White (Daylight) fluorescent lamps.Light quality was controlled by use of Rohm and Haas Plexiglas filters (5, 80) placed beneath the lamps.All light available to E. densa in the individual jars passed through these filters.Each water bath received light of different qualities.The clear filter transmitted light in the band from 360 to 740 mp., the whole visible light spectrum.The red filter permitted transmission of light from 620 to 740 mp., the red band of the visible light spectrum. The green and blue filters transmitted light from 440 to 620 mp. and 360 to 560 mp.. An overlap existed between the spectra of the green and blue filters (Appendix Figure 1).The Weston 84 Illumination meter, which is not equally sensitive at all wavelengths, was used to measure light intensity.Light intensity was 660 lux under the clear filter at the water surface.In an effort to obtain equienergetic light transmission, lamps over the colored filters were lowered or increased in number compared to the clear filter. The individual experiments were conducted at water temperatures of 10, 20, and 30 C. Water was circulated continuously through all four baths.In each experiment, diquat at 0.5 and 0.25 ppmw diquat in combination with 0.5 ppmw copper sulfate and 0.5 ppmw endothall were applied to E. densa growing under the four different light regimes.Visual evaluation of control of E. densa was made ten days after chemical treatment and at harvest.The E. densa was harvested at ten days (30 C), 21 days (20 C), and 52 days (10 C) after treatments.Visual estimation of control, length of stem, and dry weight of stem were analyzed as a three-factor analysis of variance; the factors being light quality, chemical treatments, and replications. Each experiment at 10, 20, and 30 C was analyzed separately.

Results

No significant difference in control of E. densa, as reflected in reduction of dry weight of stem, due to chemical treatment under four different light qualities was recorded (Table 4).The effect of different light qualities on control of E. densa by individual herbicide 85 1/ Table 4. Effect of light quality and chemical treatments on control of E. densa.-

Mean dry wt. (mg) Average control(%) 10C 20C 30C 10C 20C 30C

Light Quality (All chemical treatments)

Clear 768 787 877 42 38 37 Red 792 868 736 40 38 41 Green 743 871 900 47 38 40 Blue 631 822 875 55 38 41 LSD 186 113 220 O. 01 Chemical Treatment (All light qualities)

Diquat 0.5 ppmw 235 419 408 96 84 86 Diquat 0.25 ppmw 248 470 531 87 83 75 Diquat + CuS0 0.25 + 0,5 ppmw 333 639 674 86 70 70 4 Diquat + endothall 0.25 + 0.25 ppmw 450 568 317 82 80 91 Endothall 0.25 ppmw 1314 1290 1506 0 0 0 CuSO4 0.5 ppmw 1071 1151 1087 11 5 9 Control 1485 1324 1408 0 0 0 LSD 136 121 125 0.01

1/Data and statistical analyses in Appendix Tables 18 to 23. 2/ Visual estimate of E. densa control. 86 treatments was slight (Appendix Tables 17, 18, 19).At 10 C, increased effectiveness of 0.25 and 0.5 ppmw diquat applied to plants under blue light was noted.This was not the case when copper sulfate and endothall were combined with 0.25 ppmw diquat.This increase in effectiveness under blue light was not observed with the other light qualities or in the 20 and 30 C experiments. As was found in the preliminary screening trial, 0.5 ppmw diquat gave optimum control of E. densa (Table 4).Application of 0.25 ppmw diquat at 30 C resulted in significantly less control of the plant as reflected in stem dry weight reduction.At 10 and 20 C, there was no significant difference in control of E. densa between the 0.25 and 0.5 ppmw rates of diquat. Addition of 0.5 ppmw copper sulfate or 0.25 ppmw endothall to 0.25 ppmw diquat did not significantly improve control of E. densa Copper sulfate addition reduced the effectiveness of diquat at 20 and 30 C.Endothall addition resulted in some reduction of diquat activity against E. densa at 10 C and to a lesser extent at 20 C.However, at 30 C, an increase in diquat effectiveness due to endothall addition was noted (Table 4). Simple comparisons of the effect of water temperatures on E. densa control was not possible since harvest dates for each temperature were different.At 10 C, no visual control of E. densa was observed, whereas at 20 C limited effects were noted and at 30 C 87

Table 5.The effect of temperature and light qualityon the activityof diquat and diquat combination treatmentson E. densa control at 10 days after application.

ToE. densa control Light (Average4 reps.) ppmw quality 10C 20 C30 C

Diquat 0. 5 Clear 0 14 87 Diquat O. 25 0 10 65 Diquat + Endothall 0. 25+0. 25 0 20 90

Diquat 0. 5 Red 0 21 85 Diquat O. 25 0 19 80 Diquat + Endothall 0. 25+0. 25 0 32 90

Diquat 0. 5 Green 0 11 85 Diquat O. 25 0 14 81 Diquat + Endothall 0. 25+0. 25 0 24 91

Diquat 0. 5 Blue 0 15 88 Diquat 0. 25 0 9 77 Diquat + Endothall 0. 25+0. 25 0 30 89 88 complete "knockdown" had been accomplished by application of 0.5 ppmw diquat and 0.25 ppmw endothall (Table 5).Upon harvest of the E. densa, no reduction in effectiveness of 0.5 ppmw diquat treatments due to temperature difference from 10 C to 20 C to 30 C was observed (Table 4).Thus, the slower demonstration of visual effects on E. densa at the lower temperatures did not reflect reduced diquat phytotoxicity.

Field Trials

The objectives of the field work were to establish a safe, efficient technique for E. densa control in the coastal lakes and to observe the effect environmental factors had on the activity of diquat alone and in combination with endothall and copper sulfate, against E. densa.To achieve these objectives, trials were conducted in plastic pools and established at South Ten Mile Lake and Siltcoos Lake, Oregon.

Preliminary Trials

Preliminary trials, established as part of the regular screening program of the Aquatic Weed Control Project at Oregon State Univer- sity, were used to evaluate promising herbicides for E. densa and E. canadensis control. 89 Materials and Methods

Black plastic tanks, which contained soil three to four inches deep, were filled with water from Soap Creek, near Corvallis, Oregon. Preliminary Trial 1, Summer 1968, was a comparison of diquat and diquat combinations against E. canadensis. At time of application, water temperature was 24 C with a pH of 7. 6.Visual evaluations of control were made at 30 and 70 days.Preliminary Trial 2, Summer 1969, compared diquat and diquat combinations of E. densa control.Water temperature was again 24 C but pH was 8.6 at the time of application.Visual evaluations were made at 14 and 28 days.Preliminary Trial 3, Fall 1969, compared diquat and diquat combinations for control of E. densa at water temperatures which fell from 14 C at time of application to 6 C, 28 days after treatment.The pH was 7. 6 at time of treatment.Visual evaluations of control were made at 14 and 28 days.

Results

Diquat applied at 0.25 ppmw gave good control of E. canadensis and E. densa in all trials (Appendix Tables 25, 26, 27).No clear-cut advantages in E. densa control ensued from the addition of endothall or copper sulfate to diquat. When water temperatures decreased below 15 C, the speed of activity of diquat treatments was reduced 90 drastically.

Trials in Coastal Lakes

These trials were established in South Ten Mile Lake and Silt- coos Lakes where dense infestations of E. densa had been established for at least ten years.Contact and soil active herbicide applications were investigated to provide temporary control of E. densa. A uniform plot size was adopted for all trials; 50 feet by 100 feet, a plot of 0.115 acres.E. densa populations in treatment areas occupied from 70 to 100% of the water volume.Plots were outlined by stakes, buoys, and existing landmarks such as pilings.Contact herbicides were applied by a portable, boat-mounted spray unit (Plate

7).This portable unit utilized a 55-gallon drum, a small centrifugal pump, a recirculating device from drum to pump to drum, and a hand- held half-inch pipe spray gun. Once the herbicide or herbicide combination solution had been thoroughly mixed through recirculation, the surface of the plot was sprayed by a "hose-on" technique as the boat was poled across the plot.Complete surface coverage with the dilute solution was achieved three to four times by application of 200 gallons per acre solution.Plate 8 shows a plot established in Field Trial 3. The area treated can be noted in the foreground. Granular dichlobenil was applied by hand.Treatments were not replicated within a trial. Contact herbicide rates were calculated on a parts per million by 91

Plate 7.Application of experimental herbicide (SD15179) by author in Booth Arm, Siltcoos Lake, 1969.

_Aso &ILA. ..AismIIMIIII.--.A.i110

Plate 8.Control of Elodea densa with diquat at 1.00 ppmw, Field Trial 3, Fiddle Creek Arm, Siltcoos Lake, October, 1969. 92 weight basis for diquat cation, sodium endothall, and copper sulfate pentahydrate. Average depths were calculated for each plot along a transect using a sounding pole. Surface water temperature, pH, and Secchi disc readings were usually measured at time of application.In Field Trials 2 and 3, E. densa samples were taken with a weed grapnel for diquat analysis and in Field Trial 3, a limnophotometer and submersible thermistor probe were used to measure light attenuation and temperature profile.

Field Trial 1 - South Ten Mile Lake, 1968

The main objectives of this trial were to confirm reports of diquat activity against E. densa and to observe the effects of dichlobenil on a temporarily-controlled stand of this plant.

Materials and Methods

Field Trial 1 was established on the north shore of South Ten Mile Lake on July 15th, 1968 (Figure 3).At the time of application of diquat treatments (Table 6), water temperature was 21 C and the Secchi disc reading was 1.5 meters. Water levels rose rapidly within two weeks of diquat treatments because of heavy summer rains. Dichlobenil treatments (Table 6) were applied to infested and completely controlled plots on September 12th, 1968. On September 19th, 1969, two dichlobenil applications and one diquat application (Table 6) 93

Channel to North Ten Mile Lake

Lakeside 1111

Sawmill 8 cgi06 Plot 9 OM 5 Plots 1 2 34

SOUTH TEN MILE LAKE

Figure 3.Diagram of Field Trial 1, South Ten Mile Lake, 1968-1970. 94 Table 6. Herbicide treatments made in Field Trial 1, South Ten Mile Lake, 1968 and 1969. Treatments Plot no. Summer19681/ Fall1968/ Fall19643

1 3 M endothall dichlobenil 2 ppm 10 lb a. i. /A

2 3 M endothall 4 ppm

3 3 M endothall 2 ppm

4 3 M endothall 4 ppm

5 diquat + CuSO4 0.5 + 0.5 ppm

6 diquat + CuSO4 + Tryad dichlobenil dichlobenil 0.5 + 0.5 ppm 10 lb a. i. /A 10 lb a. i./A

7 Endothall K+ + Silvex K+ 2.0 ppm

8 EndothallK++ SilvexK+ dichlobenil 2.0 ppm 20 lb a. i. /A

9 diquat + Tryad dichlobenil dichlobenil 1.0 ppm 20 lb a. i. /A 20 lb a. i. /A

10 diquat diquat 1.0 ppm 0.5 ppm

1 /Plots1-4 applied 7/15/68 Plots 5-10 applied 8/2/68 21Applied9/12/68 as 4% granule by hand 3 /Applied 9/19/69as 4% granule by hand 95 were made on selected plots.Water temperature was 18.5 C, pH was 7.4, and the Secchi disc reading was 2.2 meters.Visual evaluations of control were made throughout duration of the trial until March 26th, 1970.

Results

Diquat plus copper sulfate at 0.5 ppmw and diquat alone at 1.0 ppmw gave complete control of E. densa down to the hydrosoil (Table

7). Neither addition of an experimental surfactant, Tryad, a mixture of alkyaryl (ethylenoxy) ethanol, ethyl hexylbutanolioate, and petro- leum--' distillates, to diquat nor use of an experimental (18, 26) aluminum salt formation ofendothall-3/result in control of E. densa under these conditions.The commercial mixture of endothall and silvex4/gave temporary "knockdown" of the problem plant at two ppmw. Fall applications of the dichlobenil 4% aquatic granule at 10 and 20 pounds active ingredient per acre did not control actively growing E. densa. On plots previously controlled with diquat or diquat plus

/Manufactured -2- as "Tryad" by Colloidal Products Corporation, Sausalito, California. 3/Dihydroxyaluminum salt of endothall, 3M Corporation, St. Paul, Minnesota. 4/Manufacturedas "Aquathol plus" by Pennwalt Corporation, Tacoma, Washington. 96

Table7,Control of E. densa in Field Trial 1, South Ten Mile Lake, 1968-1970,

Visual estimation of control (%)

1 3 12 14 20 Plot 1/ no. Treatments- month* months months months** months

1 endothall/ dichlobenil/ -- 0 0 0 0 0

2 endothall/--/-- 0 0 0 0 0

3 endothall/--/-- 0 0 0 0 0

4 endothall/--/-- 0 0 0 0 0

5 diquat + CuSO4 100 95 40 30 10

6 diquat + CuSO4 /dichlobenil/ dichlobenil 95 90 90 70 50

7 Aquathol plus / - - / -- 0 0 0 0 0

8 Aquathol plus/dichlobenil/ 0 0 -4**

9 diquat/dichlobenil/dichlobenil 100 90 8S 80 10

10 diquat/ --/ diquat 100 95 30 20 100

1/Summer 68 application - Fall 68 application - Fall 69 application *at time of treatment, Fall 68 'mat time of treatment, Fall 69 ***Homeowner treated with CuSO 4 97 copper sulfate, regrowth of E. densa was retarded by dichlobenil throughout the summer of 1969.Nine months after application in early summer, dichlobenil treated plots had 10 to 15% regrowth of E. densa whereas in plots treated with diquat but without dichlobenil application regrowth was 60 to 70%. Further application of dichlobenil 4% aquatic granules to partly regrown plots in September 1969 did not prevent rapid regrowth by March 1970.At the same time, an application of 0.5 ppmw diquat to an almost completely regrown 1968 diquat plot gave complete control of E. densa which lasted through March 1970.Nitella sp., an alga, was found growing densely in the plot at this time.

Field Trial 2 - Booth Arm, Siltcoos Lake, Summer 1969

This trial was established to test the efficiency of various rates of diquat alone and in combination with other herbicides for control of E. densa.

Materials and Methods

This trial was established on July 18th, 1969 on the west side of Booth Arm, at the southernmost point of Siltcoos Lake (Figure 4). Contact herbicides were applied at that date (Table 7).Dichlobenil treatments were applied on September 17th, 1969. When the contact herbicides were applied, 7:30 am to 10:30 am 98

Booth Arm

Railroad trestle

Wind direction - summer months

-- Chemical drift to this line

Figure 4.Diagram of Field Trial 2, Siltcoos Lake, 1969-1970. 99 on July 18th, the average plot depth was 2.5 meters, the water temperature at 20.5 C, pH at 7.3, and the Secchi disc reading at 3.5 meters. Water temperature remained at 20 C until September 5, 1969, when it was recorded at 18.5 C.There was no wind at time of application.Within half an hour after application, the daily, strong north wind arose and blew until dusk thus affecting contact time of the herbicide to the plant. Dichlobenil 10% granules were applied to four essentially weed- free plots on September 17th, 1969.Water temperature was 18.5 C and the Secchi disc reading was 1.5 meters.Visual evaluations of control were made on all plots at regular intervals from time of application until March 26th, 1970. Random samples of E. densa (700 gm) were collected from each diquat plot with a weed grapnel at seven and 14 days after treatment. These samples were stored in a freezer until analysis for diquat residues could be made.---/

Diquat levels were determined by a colorimetric method.Un- frozen E. densa was refluxed in sulfuric acid to free the diquat cation. The extract was neutralized and passed through a cation exchange resin to absorb diquat.This chemical was then eluted from the column with ammonium chloride and subsequently reduced by sodium

Analysis of Diquat Residues, Method R-M 5, Revised. Ortho Division, Chevron Chemical Company, Richmond, California. 100 dithionite to an unstable free radical with an intense green color and strong absorption peak at 377 mp..Plants, free of diquat, were used as checks to estimat the recovery efficiency of the method and enable calculation of diquat content of the treated samples. Absorbance of the unstable free radical was measured on a Hitachi Perkins Elmer 139 UV-VIS Spectrophotometer.

R e s ults

Results from this trial were confused by wind-aided chemical movement out of the plots and into the check areas. While such daily wind movement is an integral part of the environment of the coastal lakes, it interfered drastically with the distribution of the herbicide treatments.It was possible to determine drift effects by comparative observation of elodea growth on the west shoreline of Booth Arm to that in the trial area on the east side.The overall result of Field Trial 2 was to open up the margin of Booth Arm from Plot 8 to Plot 1 due to control of E. densa (Figure 4).Within the area designated, at least 40 to 50% control of existing elodea population was observed. No effect was noted in the elodea beds on the opposite shore (Plates 9 and 10).Approximately four gallons of diquat were used in treating various plots in an area of approximately four and one-half acres with an average depth of ten feet.Thus the overall concentration of diquat, if evenly distributed, would have been 0.1 ppmw. 101

Plate 9.East side of Booth Arm, Siltcoos Lake showing control of Elodea densa along shore due to diquat application and drift, Field Trial 2, September, 1969.

Plate 10.West side of Booth Arm, Siltcoos Lake, showing typical Elodea densa infestation, September, 1969. 102

Table 8..Control of E. densa in Field Trial 2, Booth Arm, Siltcoos Lake, 1969 -1970.

Control E. densa (%) Treatments Plot 2 4 8 12 32 no. July 18th Sept. 17th weeks weeks weeks weeks weeks

1 Diquat dichlobenil 10G 1.0 ppm 20 lbs 60 100 100 100 100

2 Diquat dichlobenil 10G 0.5 ppm 10 lbs 40 80 95 95 100

3 Diquat dichlobenil 10G 0.25 ppm 20 lbs 40 80 85 90 100

4 Diquat + CuSO4 dichlobenil 10G 0.5 + O. 5 ppm 10 lbs 70 80 95 95 100

5 Diquat + CuSO4 0.25 + 0.5 ppm 40 70 90 95 80

6 CuSO4 -- 0.5 ppm 20 35 50 40 40

7 Diquat + endothall Na 0.5 + O. 5 ppm 50 80 85 75* 70

8 Diquat + endothall Na 0.25 + 0.25 ppm 50 70 85 75* 70

9 SD 15179 CuSO4 1.0 ppm 0.5 ppm 10 10 0 0 0

10 SD 15179 endothall Na 0. 45 ppm 0. 5 ppm 0 0 0 0 0

*Regrowth 103 Evaluations made (Table 8)showed that, despite observed chemical drift, diquat at 0.25 ppmw gave excellent control of E. densa.Applications of 1.0 ppmw diquat resulted in elimination of E. densa down to the hydrosoil.This was not achieved by any of the other treatments (Table 8).Addition of 0.5 ppmw copper sulfate and 0.25 to 0.5 ppmw endothall did not enhance control obtained by 0.25 and 0.5 ppmw diquat. Dichlobenil treatments prevented regrowth in plots where diquat had controlled E. densa. On March 26, 1970, no E. densa was found in dichlobenil plots. Some growth of the alga, Nitella sp., was found in the plot treated with 1.0 ppmw diquat and 20 pounds per acre dichlobenil.In areas where E. densa had been controlled in the previous fall but no dichlobenil applied, active regrowth had commenced by March.E. densa on the west shore of Booth Arm, untreated the the previous year, was actively regrowing at the March evaluation date and the mass of plants were but one or two feet from the surface of the water in these check areas. Diquat residues in E. densa (Table 9)could not be subjected to statistical analysis since only one sample was taken from an unrepli- cated treatment.Diquat content found in treated plants at seven days ranged from 9.4 ppmw in the 1.0 ppmw diquat plot to 4.4 ppmw found in the 0.25 ppmw diquat plus 0.25 ppmw endothall plot.At 14 days diquat levels were essentially within the same range. No gross 104 Table 9.Diquat content in E. densa after treatment with diquat; Field Trial 2, Booth Arm, Siltcoos Lake, 1969. Diquat cation content (ppmw) Rate Plot no. Treatments ppmw 7 days 14 days

1 Diquat 1. 0 9. 4 11. 4

2 Diquat 0. 5 7. 1 7. 8

3 Diquat 0.25 5. 1 5. 4

4 Diquat + CuSO4 0. 5 + 0. 5 4. 5 6. 7

5 Diquat + CuSO4 0.25 + 0. 5 5. 1 3. 1

6 Diquat + endothall 0. 5 + 0. 5 5. 8 6.1

7 Diquat + endothall 0.25 + 0.25 4. 4 3. 7 105 increase in diquat uptake was found when copper sulfate or endothall was added to diquat.Application of diquat at 1.0 ppmw caused rapid "knockdown" of E. densa and resulted in the highest found diquat level. Nevertheless, diquat plus copper sulfate, each at 0.5 ppmw, exceeded 1.0 ppmw diquat in rapidity of effect yet diquat levels found in the plant were slightly lower. By seven days after treatments, most uptake of diquat by E. densa had occurred.

Field Trial 3 - Fiddle Creek Arm, Siltcoos Lake, Fall 1969

The Fiddle Creek Arm Trial (Figure 5) was a duplication of Field Trial 2 in Booth Arm. E. densa infestations were slightly more dense.The late season application was conducted in an effort to determine possible practical application problems and to obtain further data on the activity of diquat combination treatments on the control of E. densa.

Materials and Methods

This trial was established on September 18th, 1969.The average plot depth was 2.5 meters. Siltcoos Lake was one meter below normal level because of water removal for railroad maintenance. Fall rains of three to four inches on September 17th, 18th, and 19th 1969 kept the water level from dropping further until September 21st. The turbidity level of the Fiddle Creek stream was raised because of 106

Plot 2

CSZ CD Plot 3 `C] Boathouse Plot 1 ...,,_ at:7 .Plot 4 % \ Plot 5 \\ a Fiddle Creek Plot 6

Arm Fiddle Creek Flow

Plot 7

Chemical drift to this line

Figure 5.Diagram of Field Trial 3, Siltcoos Lake, 1969-1970. 107 this rainfall and therefore turbidity in Plot 7 and water movement in Plots 3, 4,5, and 6 occurred. Herbicide treatments (Table 10) were applied from 8: 00 to 10:00 am. Surface water temperature was 18.4 C and the Secchi disc reading was 1.6 meters.E. densa samples were harvested at nine and 18 days after treatment.The system utilized for collection and diquat analysis was that outlined for Field Trial 2.Visual evaluations of control were made at regular intervals after treatment. A submersed limnophotometer and thermistor probe were used to measure light attenuation and temperature profile in "weedy" and "non-weedy" areas of Fiddle Creek.

Results

Water temperature dropped from 18.4 to 10.0 C within four weeks after treatment.The rate of activity of both diquat and diquat combination treatments was reduced in comparison to Field Trial 2 where the average water temperature was 20 C (Table 10). By March, 1970 no difference in overall control due to this temperature differential between the two trials could be noted. Diquat applied alone was effective for control of E. densa at rates as low as 0.25 ppmw. Combination of endothall and copper sulfate did not noticeably enhance diquat activity nor did they achieve the slight speeding-up of diquat activity noted in Field Trial 2. Some 108 Table 10.Control of E. densa in Field Trial 3, Fiddle Creek Arm, Siltcoos Lake, 1969-1970.

Plot 2 4 8 24 no. Treatments weeks weeks weeks weeks

1 Diquat 1.0 ppm 30 70 90 100

2 Diquat 0.5 ppm 20 65 70 90

3 Diquat 0.25 ppm 15 60 70 85

4 Diquat + CuSO4 0. 5 + 0. 5 ppm 15 60 70 90

5 Diquat + CuSO4 0.25 + 0. 5 ppm 25 70 80 90

6 Diquat + endothall Na 0. 5 + 0. 5 ppm 10 50 80 80

7 Diquat + endothall Na 0.25 + 0.25 ppm 10 30 50 50

8* CuSO4 0.5 ppm 0 0 0 0

9* endothall Na 0.5 ppm 0 0 0 0

*Plots 8 and 9 were located in Booth Arm (see Table 12). 109 chemical movement out of Plots 3,4,5, and 6 may have prevented full expression of combination activity as occurred in Field Trial 2. Turbid water in Plot 7 assuredly reduced the effectiveness of the diquat plus endothall treatment. By March 26th, control from diquat at 0.25 ppmw was almost equal to that from combination treatments. Diquat analyses (Table 11) show generally higher rates of uptake by the diquat alone treatments both in comparison to combination treatments in Field Trial 3 but also to comparable treatments in Field Trial 2.This is possibly due to the fact that little,if any, water movement could occur or was observed in these plots (Figure

5).In Plots 3 through 7, water movement did occur within 24 hours after treatment because of the flood waters from Fiddle Creek stream. As water temperatures were virtually similar in Field Trials 2 and 3 during the first week after application, the similarity of levels of diquat uptake between Plots 3 and 7 in both trials could be expected. At nine days, diquat levels ranged from 26.9 ppmw diquat in the 1.0 ppmw diquat treatment to 5.7 ppmw for 0.25 ppmw diquat and 0.25 ppmw endothall treatment. At 18 days levels were generally comparable to those measured nine days previously.In the area outside the trial, affected by diquat movement in flood waters, a diquat level of 2.4 ppmw was detected in exposed E. densa. It was noted that in Field Trial 3, much of the apical portions of E. densa in the plots were covered with macroscopic colonies of 110

Table 11.Diquat content in E. densa after treatment with diquat; Field Trial 3, Siltcoos Lake. Diquat cation con- Rate tent (ppmw) Plot no. Treatments ppmw 9 days 18 days

1 Diquat 1. 0 27. 0 25. 1

2 Diquat 0.5 25.7 22.9

3 Diquat 0.25 3.4 9.4

4 Diquat + CuSO4 0. 5 + 0. 5 28. 3 7. 3

5 Diquat + CuSO4 0.25 + 0. 5 8. 5 9. 5

6 Diquat + endothall 0. 5 + 0. 5 10.8 11. 3

7 Diquat + endothall 0.25 + O. 25 5. 7 4.9 111 the alga, Microcystis sp.Such growths were not present on E. densa in Field Trial 2.No decrease in diquat uptake was associated with this algal growth.These algal growths were heaviest in the treated areas of the Fiddle Creek Trial. In open water, measurable light penetrated to the hydrosoil at three meters whereas in the "weedy" areas, no light could be measured below 0.5 meters (Appendix Table 30).In both open and "weedy" areas, light in the green portion of the visible light spectrum penetrated in greatest quantity. A thermocline had not developed in open or "weedy" areas (Appendix Table 30). 112

DISCUSSION AND CONCLUSIONS

Laboratory Trials

Studies have demonstrated that native submersed aquatic plants found in coastal lakes, E. canadensis, C. demersum, and M. verticillatum could be readily controlled by diquat applications alone or in combination with copper sulfate or endothall.The concept of control with contact herbicides isdisintegration of submersed plants' leaves and stems down to the hydrosoil.Control will thus be temporary, if the specific plant, such as E. densa, hasvigorous rootstocks in the hydrosoil.Control with a soil-active herbicide depends on uptake by these roots and should, in theory, be longer last- ing on rooted hydrophytes than control by contact herbicides. The time of herbicide application is one variable readily controlled in the field by the operator. Thus far, no quantitative data has been developed to guide those who apply diquat.Whitely (81) indicated that evening applications of diquat had given best results for submersed weed control in Missouri.In the Oregon lakes, months with highest water temperature are those with constant, strong winds which blow from late morning to early evening. Time of application could, therefore, influence chemical drift from treated areas during these summer months. Under laboratory conditions at 20 C, superior E. densa control was obtained when 0.25 ppmw diquat alone or in 113 combination with 0.5 ppmw copper sulfate were applied at the beginning or middle of the light period.Applications at the beginning or middle of the dark period were significantly less effective although acceptable control was obtained.All field applications were made between the beginning and middle of the daily light period. Optimum exposure time of E. densa to diquat had previously been established in Oregon (26) at 24 hours for 1.0 ppmw diquat.In laboratory trials reported above, 0.25 ppmw diquat controlled E. densa at 30 C after six hours exposure. At 20 C, 24 hours exposure was required for optimum effect although six hours exposure still resulted in 78% control of E. densa. Upon reduction of temperature to 10 C, the optimum exposure time remained at 24 hours with 75% control recorded after 12 hours exposure. On this basis, under field conditions, diquat exposure times less than 24 hours caused by wind and water movement in 20 C water would not result in less acceptable control than that achieved with the longer exposure time required in lower water temperatures encountered during the less windy fall months.It is also possible that flood-water induced movement in fall months would result in short exposure times in the field when water temperatures are lower. Effects of water temperature on diquat activity are not documented. Results on terrestrial plants indicated that effectiveness of low rates of bipyridyl herbicides would be inhibited by lower 114 temperatures.Laboratory studies showed that expression of diquat phytotoxicity on E. densa was delayed but not prevented by lower temperatures.Eventual control by 0.25 ppmw diquat, a low rate, at 10 C was equal to that achieved at 30 C. Increase in light intensity has been shown by Blackburn and Weldon (17) and Davies (44) to enhance diquat activity on Lemna sp. and E. canadensis. Comparative studies were not made with E. densa.Control obtained with 0.25 ppmw diquat at 20 C was greater in trials conducted in the wooden water baths where light intensity was 1600 lux, than in the metal water bath trial where light intensity was 660 lux in the baths exposed to the full visible light spectrum. Light quality was varied in the laboratory to determine possible methods to increase diquat effectiveness of E. densa control. No significant differences in effectiveness were noted when diquat and diquat plus copper sulfate or endothall were applied to E. densa grown under the full visible light spectrum, red light, green light, or blue light.This was true at water temperatures of 10, 20, or 30 C.This lack of difference in diquat activity under different light qualities is in marked contrast to the results of Blackburn and Weldon (17), who reduced injury to Lemna sp. from 0.1 ppmw diquat by 40 to 60% under blue and bluegreen light in comparison to the more effective orange-red light.No effects of green light on diquat activity were noted in the laboratory.In Field Trial 3, green light was attenuated 115 less than other bands of the visible light spectrum in "weedy" or open water.Application of dyes to the water surface, thus excluding certain bands of the visible light spectrum, does not appear to offer a means to increase diquat effectiveness in field situations. The addition of copper sulfate to diquat has resulted in synergistic effects on H. verticillata in laboratory and field studies in Florida as demonstrated by Blackburn (19) and Mackenzie (104).However the use of copper sulfate is not encouraged in Oregon at rates above 0.5 ppmw where cold water fish species are present.At 20 C, in laboratory and field, addition of 0.5 ppmw copper sulfate to 0.25 ppmw diquat did not give enhanced control.In fact, at 20 and 30 C in the laboratory under low light intensity, antagonistic effects were noted.Under the higher light intensity in the wooden water baths, no synergistic effects were recorded.The low rate of copper sulfate must be below a threshold value, possibly 1. 0 or 2.0 ppmw copper sulfate, utilized by Blackburn and Mackenzie in their studies. Potassium endothall was claimed by Corning and Prosser (39) to be synergistic with diquat on E. densa.They did not demonstrate that the 0.25 ppmw endothall plus 0.25 ppmw diquat treatment was superior to 0.25 ppmw diquat alone, only that it was as effective as 0.46 ppmw diquat.In the laboratory at 20 C and in field studies, no advantage could be attributed to combinations of diquat with endothall. At 10 C, reduced activity at temperatures below 15 to 19 C (130, 173) 116 could explain such antagonism.Certainly at 30 C, endothall showed a slight enhancement of diquat activity.This was not significant at the 1% level.

Field Trials

In the South Ten Mile and Siltcoos Lakes, application of 0.25 ppmw diquat resulted in seasonal control of E. densa infestations. The degree of control achieved was not quite equal to that obtained from 1.0 ppmw diquat.Nevertheless, availability of previously infested waters to angling activities was not increased significantly by use of the higher application rate.The season following application of diquat, substantial regrowth resulted even where 1.0 ppmw diquat had controlled E. densa growth down to the hydrosoil, a result not completely achieved by 0.25 ppmw diquat.Control ratings of 85 to 90% recorded with 0.25 ppmw diquat application represent sparse E. densa stem growth, six inches in height.This represents satisfactory seasonal control.This degree of control at 0.25 ppmw diquat has not previously been reported.Results from Florida (14) indicated that 1.0 ppmw diquat was required for complete control; 0.36 ppmw gave but 30% "knockdown" in one study.Limited Oregon trials (26, 27, 90) had also indicated that 1.0 ppmw was required to give complete seasonal control of E. densa. Addition of copper sulfate did not improve field control of E. 117 densa in two trials.With or without 0.5 ppmw copper sulfate, 0.25 ppmw diquat resulted in 85 to 90% control.Addition of endothall at rates equal to that of diquat did not enhance control of E. densa under Oregon conditions.Blackburn (14) had reported lack of success with endothall combinations for control of H. verticillata.Addition of copper sulfate or endothall did not increase diquat residue levels in treated plants. Dichlobenil was applied to plots previously treated with diquat, endothall or diquat with copper sulfate. No control was obtained where 10 and 20 pounds active chemical was applied as a single treatment to dense infestations of E. densa. Where successful contact control had been achieved with other herbicides prior to dichlobenil application, E. densa regrowth was temporarily suppressed the following season to a greater extent than that observed in the diquat- treated plots, free of E. densa at time of dichlobenil application.Re- growth, however, was significant in dichlobenil plots 12 months after application.Retreatment of this regrowth with dichlobenil was unsuccessful and further contact herbicide application was necessary 18 months after the original diquat application.In the South Ten Mile Lake Trial, a second application of diquat was made 15 months after a successful diquat treatment.Six months later no regrowth was noted and Nitella sp., a plant-like alga, had invaded the plot area. A similar successional pattern was observed in other plots in Ten Mile 118 Lake and in Siltcoos Lake. Invasion of this low growing alga could be regarded as desirable in that such algae support (117) large numbers of fish-food organisms and yet would represent less interference with angling activities. Reduction of water temperature from 18 C to 10 C during one month after application in Field Trial 3, did not reduce the eventual effectiveness of diquat applications.Expression of phytotoxicity was delayed in comparison to similar treatments in Field Trial 2 where water temperature did not drop below 20 C during the same one month period after treatment. Observed diquat levels in plants were not reduced by decreased temperatures following application.Diquat uptake was found to occur (44) most rapidly in the first few hours after exposure.Field results with E. densa substantiated laboratory observations (44, 145) which show diquat uptake to be a rapid physical process rather than a slower metabolic process.Levels of diquat in sampled plants reached 11 ppmw in the 1.0 ppmw diquat treatment despite the short contact period.Further evidence for rapid diquat uptake is supplied by the fact that wind-induced chemical movement within two to four hours after application reported in Trial 2,still allowed for sufficient uptake of diquat to cause "knockdown" of E. densa in treated areas. An estimated concentration of 0.1 ppmw diquat in drift-affected areas, resulted in complete defoliation and partial stem "knockdown" up to 50 to 70% control in some areas. 119 While not completely acceptable, this level of control indicates possible merit for investigation into repeated 0.1 ppmw diquat treatments for E. densa control. Results obtained in Field Trial 3, where flood waters caused turbidity in one plot, indicate one drawback to application in the fall. Despite the calmer climatic conditions of fall and reduced possibility of wind-induced chemical drift from treated areas, unexpected arrival of fall rains could result in loss of diquat in treated areas exposed to creek flood waters carrying heavy silt loads.Absorption of diquat on silt (56, 186) would account for loss of activity.No advantage in terms of overall control has been demonstrated from fall applications although higher levels of diquat, up to 26 ppmw in sampled plants, were recorded in Trial 3. Repeated application of 0.25 ppmw diquat is the safest and most effective method of E. densa control available for the coastal lakes of Oregon. These applications can be made successfully in summer months despite wind-induced water movement.Fall application is also a practical possibility despite reduced water temperatures.

Conclusions from Field and Laboratory Studies

It was concluded that:

1) seasonal control of E. densa was achieved by application of 0.25 ppmw diquat under field conditions in the coastal lakes 120 of Oregon'

2) water movement induced by wind and flood water dissipated diquat applied to small plots

3) no real advantage was found for fall application over summer application in the field

4) light quality did not affect diquat activity against E. densa

5) water temperature did not affect activity of diquat against E. densa at exposure times of 24 hours or longer

6) optimum exposure time for diquat against E. densa was six hours at 30 C and 24 hours at 10 and 20 C while acceptable control was obtained at two hours for 30 C, six hours for 20 C, and 12 hours for 10 C.

7) addition of low rates of copper sulfate or disodium endothall did not enhance diquat activity against E. densa

8) application of diquat during daylight hours was superior to application at the beginning of or during the dark period

9) diquat plus dichlobenil applications did not extend the control period of E. densa further than that achieved by two diquat applications

10) further study is required on the long term control of E. densa by repeated low-rate diquat applications. 121 Proposal for Practical Application of Research Findings

At the time of writing, the coastal lakes are still infested with E. densa, an exotic submersed plant which occupies large areas of these lakes.These lakes support a varied population of sport fishes. Angling represents the major recreational use of these lakes. Use of the lakes for swimming and water skiing is slight.Sport fishing is mainly practiced along the shorelines where growth of E. densa is most dense. Use of deeper water for "trolling" or bottom fishing occurs less frequently.Although infestations of E. densa are reduced in winter months, dormant stands can be observed during the months of January, February, and March; months when bass fishing is popular. Use of the lakes for transportation purposes is infrequent since log rafting is no longer practiced on Siltcoos or Tahkenitch Lakes. Accessibility of remote areas by boats is not denied by current infestations of E. densa.Control of E. densa would possibly benefit recreational fishermen and the tourist business which rely wholly or partially on the sport fishing resources of the coastal lakes.Anglers still visit and fish the lakes despite the weed infestations.Complete eradication of vascular aquatic plants is not desirable since production of important fish food organisms would be curtailed.Under these circumstances, what techniques can be used to control E. densa 122 infestations in areas important to anglers? What impact will such limited plant removal have on fish production,angler success and hence on the local recreation-based economy? Research investigations have been conducted since 1948. Saltzman (138, 139) noted that comprehensive programs for control of E. densa infestations and evaluation of the economic importance of the coastal lakes did not exist.Using the above conclusions as a basis for action, I propose that a multidisciplinary project be established on one of the coastal lakes to:

1) evaluate long term use of diquat to keep selected fishing areas free of E. densa in Siltcoos Lake

2) evaluate the effect of repeated applications of diquat on fish, benthos, and plankton populations associated with treated areas

3) evaluate the effect of weed-free areas on angler-success and hence evaluate justifications for a large scale weed control project

4) evaluate the overall economic value of the coastal lakes to Oregon's economy. Stevens (153) felt that recreational demand curves could be utilized to evaluate the effect of fishing habitat improvements, provided that biological information was available. I propose that this pilot study be established on Siltcoos Lake 123

Keichle Arm

Siltcoos River

Fiddle Creek Arm

Field Trial 3

Booth Arm

Scale Proposed pilot 0 1 study treatment area mile Field Trial 2

Figure 6.Map of Siltcoos Lake showing location of Field Trial 2, Field Trial 3 and the proposed pilot study in Keichle Arm. 124 (Figure 6) in Keichle Arm. Access to this inlet is convenient for anglers while, at this time, it is densely infested with E. densa. Treatment of a 50 foot shoreline strip with diquat at 0.25 ppmw could be made around Keichle Arm. Pertinent information on angler success and dynamics of faunal production could be gathered prior to this treatment. Cost of shoreline treatments of 50 feet with 0.25 ppmw diquat, application cost not included, would be approximately $410 per mile (Appendix Table 31).Followup treatment with dichlobenil at ten pounds active per acre would cost $730 per mile for chemical alone.I recommend that diquat be applied as required for control of regrowth at $410 per mile rather than the more expensive dichlobenil treatment. The results of university and state sponsored research on weed infestations should have practical application. A relatively safe treatment has been developed for control of E. densa infestations. The proposed pilot study would give concrete evidence of the state's commitment to the alleviation of the E. densa problem. 125 BIBLIOGRAPHY

1. Akhavein, A. A. and D. L. Linscott.The dipyridylium herbicides, paraquat and diquat.Residue Reviews 23:97-145. 1968. 2. Alabaster, J. S.Estimating the effects of herbicides on fish. Proceedings European Weed Research Council International Symposium Water Weeds. Oldenburg, West Germany.1967. p. 178-180. 3. Aldrich, F. D. Some factors affecting the growth of Anacharis densa (Planchon) Victorin. Master's thesis.Corvallis, Oregon State College.1953.43 numb. leaves.

4. Amon, J.Economizing in the use of Gramoxone. Tea 5:23. 1964.

5. Ashton, Floyd M. Relationship between light and toxicity symptoms caused by atrazine and monuron. Weeds 13: 164 -168. 1965.

6. Austin, W. G. L.Control of aquatic weeds. Outlook on Agri- culture 4:35-42.1963.

7. Bailey, T. A. Commercial possibilities of dehydrated aquatic plants.Proceedings 18th Southern Weed Conference: 543-551. 1965.

8. Baldwin, B. C., A. N. Dodge and N. Harris. Recent advances in studies of the mode of action of the bipyridylium herbicides. Proceedings 9th British Weed Control Conference: 639 -644. 1968. 74 9. Ball, R. C. and F. H. Hooper. Use ofAs-tagged sodium arsenite in a study of effects of herbicide on pond ecology.Iso- topes in Weed Research, I. A. E. A. Vienna, Austria.1966. p. 149-163.

10. Bartley, T. R.Progress report on evaluation of copper for aquatic weed control and herbicide residues in irrigation systems. Bureau of Reclamation Report No. WC-32. United States Department of Interior.1967.p. 5. 126

11. Beasley, P. G., J. M. Lawrence and H. H. Funderburk, Jr. The absorption and distribution of 14C labelled diquat in the goldfish, Carassius auratus L.Proceedings 18th Southern Weed Conference: 581.1965.

12. Bennet, G. W. The bass-bluegill combination in a small artificial lake.Illinois Natural History Survey Bulletin 24: 377- 412.1948.

13. Bill, S. M. The water weed problem in Australia.Hyacinth Control Journal 8:1-6.1969.

14. Blackburn, R. D.Evaluating herbicides against aquatic weeds. Weeds 11:21-24.1963.

15. Blackburn, R. D., L. E. Bitting and L. W. Weldon.Control of elodea in a residential situation.Hyacinth Control Journal 5: 36-38.1966.

16. Blackburn, R. D., J. M. Lawrence and D. E. Davis.Effect of light intensity and quality on the growth of Elodea densa and Heteranthrera dubia. Weeds 9:251-257.1961.

17. Blackburn, R. D. and L. W. Weldon. The sensitivity of duck- weeds (Lemnaceae) and Azella to diquat and paraquat. Weeds 13:147-149.1965.

18. A new approach to aquatic weed control. Proceedings 22nd Southern Weed Science Society: 315.1969.

19. U.S.D.A. technical report on controlling Hydrilla verticillata,Weeds, Trees and Turf 8:20-24.1969.

20. Blackburn, R. D., L. W. Weldon, R. R. Yeo and T. M. Taylor.Identification and distribution of certain similar appear- ing submersed aquatic weeds in Florida.Hyacinth Control Journal 8:17-21.1969.

21. Blackburn, R. D., P. F. White and L. W. Weldon. Ecology of submersed aquatic weeds in South Florida canals. Weed Science 16:261-266.1968.

22, Blanchard, J. L. How one city manages aquatic weeds. Weeds, Trees and Turf 8: 18 -19.1969. 127 23. Blok, E.Experiments with herbicides in fishing waters (1964- 1967).Proceedings European Weed Research Council Inter- national Symposium Water Weeds, Oldenburg, West Germany. 1967.p. 51-64.

24. Blondeau, R.Aqua lin herbicide--a new weed killer for submersed aquatic vegetation.Proceedings 12th annual California Weed Conference:9-12.1960.

25. Bond, C. E.Annual Report with Summation of activities, 1949- 1955. Oregon Agricultural Experiment Station, Aquatic Weed Control, Project 34.1955.40p,

26. Progress report on aquatic weed research (Projects 773 and 294). Oregon Agricultural Experiment Sta- tion.1966.24p.

27. Progress report on aquatic weed research (Project 773).Oregon Agricultural Experiment Station.1967. 14p.

28. Personal communication. Oregon State University, Corvallis, Oregon.1969.

29. Bond, C. E., R. H. Lewis and J. L. Fryer.Toxicity of various herbicides and herbicidal materials to fish. Robert A. Taft Sanitary Engineering Center.Technical Report W-60 -3.1960. p. 96-101.

30. Bovey, R. W. and F. S. Davis.Factors affecting the phytotoxicity of paraquat. Weed Research 7: 281 -289.1967.

31. Bovey, R. W. and F. R. Miller.Phytotoxicity of paraquat on white and green Hibiscus, Sorghum and Alpina leaves. Weed Research 8: 128 -135.1968.

32. Boyd, C. E.Evaluation of some common aquatic weeds as possible foodstuffs.Hyacinth Control Journal 7:26-27.1968.

33. Brian, R. C.Darkness and the activity of diquat and paraquat on tomato, broad bean and sugar beet.Annals of Applied Biol- ogy 60: 77-85.1967.

34. Bryant, C. Brate.Aquatic weed harvesting.Weeds, Trees and Turf 8: 14-17.1969. 128 35. Carter, E. A.Personal communication. Ortho Division, Chevron Chemical Company, Dallas, Texas.1966.

36. Colby, S. R.Calculating synergistic and antagonistic responses of herbicide combinations. Weeds 15:20-22.1967.

37. Cope, Oliver B.Pesticides in the environment and their effects on wild life.Journal of Applied Ecology 3 (Supplement): 33-44.1966.

38. Cope, Oliver B., J. P. McCraren and L. Eller.Effects of dichlobenil on two fish pond environments. Weed Science 17: 158-165.1969.

39. Corning, R. V. and N. S. Prosser. Elodea control in a potable water supply reservoir.Hyacinth Control Journal 8: 7 -16. 1969.

40. Cottom, G.Ecological features of eutrophication.Presented at Symposium on Eutrophication, 10th Meeting of Weed Science Society of America. Montreal, Canada.1970.

41. Cowell, B. C.The effects of silvex on aquatic vegetation and plankton in Central N. Y. Farm Ponds. Down to Earth 21: 19 20.1965.

42. Crosby, D. G. and R. K. Tucker.Toxicity of aquatic herbicides to Daphnia magna. Science 154:289-290.1966.

43. Currier, H. B. and C. Y. Shih.Sieve tubes and callose in elodea leaves. American Journal of Botany 55: 145 -152.1968.

44. Davies, P. J. and D. E. Seaman. Uptake and translocation of diquat in elodea.Weed Science 16:293-295.1968.

45. The tetrazolium reaction as a measure of the action of diquat in elodea. Weed Science 16:329-331.1968.

46. Dearman, A. V.Personal communication. Ortho Division, Chevron Chemical Company, Richmond, California.1970.

47. De Vaney, Thomas E.Chemical vegetation control manual for fish and wildlife management programs. Bureau of Sports Fisheries and Wildlife, Washington, D. C. Resource Publica- tion 48.196a.p. 42. 129 48. Di Costanzo, C. J.Growth of bluegill (Lepomis machrochirus) and pumpkinseed (L. gibbosus) of Clear Lake, Iowa.Iowa State College Journal of Science 32: 19 -34.1957.

49. Eady, F. and A. J. Renney.Tolerance of Eastern brooktrout eggs to diquat. Research Report, National Weed Control Com- mittee, Western Section: 234-235.1965.

50. Eipper, A. W. and H. B. Brunsted. How to control weeds and algae in farm ponds.Cornell Extension Bulletin 1014. New York State College of Agriculture.1958.32p.

51. Emond, G.Acrolein as a chemical herbicide for submerged aquatic plants.Phytoprotection 44: 65-68.1963.

52. Faust, S. D. and A. Zarins.Interaction of diquat and paraquat with clay minerals and carbon in aqueous solutions.Resi- due Reviews 24:151-170.1969.

53. Fish, G. R. Some effects of the destruction of aquatic weeds in Lake Rotoiti, New Zealand. Weed Research 6:350-358. 1966.

54. Fish, G. R. and G. M. Will.Fluctuations in chemical composition of two lake weeds from New Zealand. Weed Research 6: 346-349.1966.

55. Flanagan, J. H.Progress report on use of simazine as an algicide and aquatic herbicide.Proceedings 19th Southern Weed Conference: 387-392.1966.

56. Fox, W. B.Aquatic weed control with diquat. Research Re- port, National Weed Control Committee, Eastern Section: 136- 137.1963

57. Foy, C. L. and S. W. Bingham. Some research approaches towards minimizing herbicidal residues in the environment. Residue Reviews 29: 105-135.1969.

58. Frank, P. A. and R. D. Comes. Herbicidal residues in pond water and hydrosoil. Weeds 15:210-213.1967.

59. Frank, P. A. and R. H. Hodgson. A technique for studying absorption and translocation in submersed plants.Weeds 12: 81-82.1964. 130

60. Frank, P. A., N. E. Otto and T. R. Bartley.Techniques for evaluating aquatic weed herbicides. Weeds 9: 515-521.1961.

61. Funderburk, H. H., Jr. and J. M. Lawrence. Absorption and translocation of radioactive herbicides in submersed and emersed aquatic weeds. Weed Research 3:304-311.1963.

62. Mode of action and metabolism of diquat and paraquat. Weeds 12:259-264.1964.

63. Gerloff, G. C. and P. H. Krombholtz. Tissue analysis as a measure of nutrient availability for the growth of angiosperm aquatic plants.Limnology and Oceanography 11: 529 -537. 1966.

64. Gibbs, K. C.The estimation of recreational benefits resulting from an improvement of water quality in Upper Klamath Lake.Ph. D. thesis.Corvallis, Oregon State University. 1969.101 numb. leaves.

65. Gilderhus, P. A.Effects of diquat on bluegills and their food organisms.Progressive Fish Culturist 29: 67-73.1967.

66. Grzenda, A. R., H. P. Nicholson and W. S. Cox.Persistence of four herbicides in pond water. Journal of American Water Works Association 58: 326-332.1966.

67. Hale, Frank E.The use of copper sulfate in control of micro- scopic organisms.Phelps Dodge Refining Corporation, New York, New York.1925.44p. 68. Hammerton, J. L.The environment and herbicide performance.Proceedings 9th British Weed Control Conference: 1008- 1110.1968.

69. Harp, G. L. and R. S. Campbell.Effects of the herbicide silvex on the benthos of a farm pond.Journal of Wildlife Management 28: 308-317.1964.

70. Hasler, A. D.Cultural eutrophication is reversible.Bio- science 19: 425-431.1969.

71. Broad aspects of eutrophication and management of aquatic weed growth.Presented at Symposium on 131 Eutrophication, 10th Meeting of Weed Science Society of America. Montreal, Canada.1970.

72. Hasler, A. D. and E. Jones.Demonstration of the antagonistic action of large aquatic plants on algae and rotifers.Ecology 30:359-364.1949.

73. Headford, D. W. R. An improved method of control of Paspalum conjugatum with Amitrole-T and paraquat. Weed Research 6:304-313.1966.

74. Highsmith, Richard M., Jr., J. G. Jensen and R. D. Rudd. Conservation in the United States.Rand McNally and Company. Chicago, Illinois.2d ed.1969.p. 407.

75. Hilsenhoff, W.Effect of diquat on aquatic insects and related animals.Journal of Economic Entomology 59: 1520 -1521. 1966.

76. Hiltibran, R. C.Duration of toxicity of endothall in water. Weeds 10:17-19,1962.

77. Effect of endothall on aquatic plants. Weeds 11:256-257.1963.

78. The effect of diquat on aquatic plants in central Illinois.Weeds 13: 71-72.1965.

79. Effects of some herbicides on fertilized fish eggs and fry.Transactions American Fisheries Society 96: 414-416.1967.

80. Hodgson, R. H. and N. E. Otto.Pond weed growth and response to herbicides under controlled light and temperature. Weeds 11:232-237.1963.

81. Holm, L. G., L. W. Weldon and R. D. Blackburn. Aquatic weeds. Science 166:699-709.1969.

82, Houser, A.Loss of weight of sunfish following aquatic vegetation control using the herbicide silvex.Proceedings of Okla- homa Academy of Science 43:232-237.1962.

83. Hudson, M. S. and B. Hudson. A laboratory test for screening chemicals for toxicity to submerged aquatic plants. Weeds 5 :37 -373.1957. 132 84. Hughes, E. C. and P. Friese.Herbicide trials on aquatic weeds. Research Report, National Weed Control Committee, Western Section:236.1965.

85. Hughes, Janice S. and J. T. Davis. Comparative toxicity to bluegill sunfish of granular and liquid herbicides.Proceedings of Southeastern Game and Fish Commissioner's Annual Meet- ing:10.1962.

86. Median tolerance limits reported in parts per million of bluegill sunfish to herbicides tested during 1961-1962.Louisiana Wildlife and Fisheries Commission. 1963.3p.

87. Jennings, R. C.The commercial use of diquat in U.K. for the control of submersed waterweeds. Proceedings European Weed Research Council International Symposium Water Weeds. Oldenburg, West Germany.1967.p. 109-112.

88. Jeschke, W. D. and W. Simonis. Uber die aufnahme von phosphat and sulfationen durch blatter von Elodea densa. Planta 67:6-32.1965.

89. Jordan, F. A.Ecology, conservation and human behavior. Bioscience 18:1023-1029.1969.

90. Juntunen, E. T. and C. E. Bond.Progress report, research on aquatic weed control (Project 773). Oregon Agricultural Experiment Station.1968.14p, 91. Keckemet, Obern. Chemical, toxicological and biological properties of endothall.Hyacinth Control Journal 8: 50-51. 1969.

92. Kerns, 0. E., Jr.The effects of experimental herbicide treatments on the fish environment in Siltcoos Lake, Oregon. Master's thesis.Corvallis, Oregon State College.1955.84 numb. leaves.

93. Kibby, H. V.Toxicity of selected herbicides to four species of fresh water fish.Master's thesis.Corvallis, Oregon State College.1966.53 numb. leaves,

94. King, L. G. Responses of Elodea densa to growth regulatory substances.Botanical Gazette 105: 127 -151.1943. 133 95. Lawrence, J. M. Aquatic herbicide data.United States De- partment of Agriculture.Washington, D. C.Agriculture handbook No. 231.1966.133p.

96. Lawrence, J. M., P. G. Beasley and H. H. Funderburk, Jr. Water quality in plastic pools, containing aquatic plants, before and after treatments with bipyridylium compounds.16th Proceedings Southern Weed Conference: 366 -367.1963.

97. Leonard, J. W. The use of herbicides in conservation.Pro- ceedings 13th Annual Meeting Northeast Weed Control Con- ference: 19 -25.1959.

98. Little, E. C. S.The control of water weeds. Weed Research 8: 105.1968.

99. Lowenhaupt, B.The transport of calcium and other cations in submerged aquatic plants.Biological Reviews 31: 371 -395. 1956.

100. McKee, J. E. and H. W. Wolf.Water quality criteria. California State Water Quality Control Board, Sacramento, California.Publication 3-A. 1963.540p.

101. Macek, K. J., C. Hutchinson and 0. B. Cope.The effects of temperature on the susceptibility of bluegills and rainbow trout to selected pesticides.Bulletin for Environmental Contamination and Toxicology 4: 174 -183.1969.

102. Mackenthun, K. M. and W. M. Ingram.Biological associated problems in fresh water environments.United States Depart- ment of Interior.Federal Water Pollution Control Administra- tion.Washington, D. C.1967.297p.

103. Mackenzie, J. W. Factors affecting control of Florida elodea in Southeast Florida Canals.Hyacinth Control Journal 8: 13- 16.1969.

104. Mackenzie, J. W. and L. Hall.Elodea control in Southeast Florida with diquat.Hyacinth Control Journal 6: 37 -44.1967.

105. Martin, A. C. and F. M. Uhler.Food of game ducks in the United States and Canada.United States Department of Agri- culture.Washington, D. C.Technical bulletin No. 634. 1939.56p. 134 106. Mason, R.Three water weeds of the family Hydrocharitaceae in New Zealand. New Zealand Journal of Science 3:382-395. 1960.

107. Merkle, M. G., C. L. Leinweber and R. W. Bovey. The influence of light, oxygen and temperature on the herbicidal properties of paraquat.Plant Physiology 40:832-835.1965.

108. Meyer, B. S.The daily cycle of apparent photosynthesis in a submerged aquatic. American Journal of Botany 26: 755-760, 1939.

109. Meyer, B. S. and A. C. Heritage.Effect of turbidity and depth of immersion on apparent photosynthesis in Cerato- phyllum demersum. Ecology 22: 17 -22.1941.

110, Meyer, B. S., F. H. Bell, L. C. Thompson and E. I. Clay. Effects of depths of immersion on apparent photosynthesis in submerged vascular aquatic plants.Ecology 24: 393 -399. 1943.

111. Meyer, F. A.Aquatic plant control.Department of Fish and Game, California. Sacramento, California.Inland Fisheries Administrative Report No. 64-2.1964.1032p.

112. Moyle, J. B. Some chemical factors influencing the distribution of aquatic plants in Minnesota. American Midland Naturalist 34: 402-420.1945,

113. Aquatic invertebrates as related to large aquatic plants and wild fowl.Minnesota Department of Con- servation, Minnesota.St. Paul, Minnesota.Investigational Report No. 233.1961.24p.

114. Muenscher, W. C.Aquatic plants of the United States. Comstock Publishing Company, Cornell University, Ithaca, New York.1944.373p,

115, Mulligan, H.Eutrophication and management of aquatic weed growth.Presented at Symposium on Eutrophication.10th Meeting Weed Science Society of America. Montreal, Canada. 1970.

116. Mulligan, H. and A. Baranowski. Growth of phytoplankton and vascular aquatic plants at different nutrient levels.Verh. Internat. Verein, Limnol, 17: 802 -810.1969. 135 117. Needham, P. R.Trout streams.Holden-Day Inc. San Francisco, California.241p.1938.Revised by C. E. Bond. 1969.

118. Nelson, J. W. et al.University of Minnesota Agricultural Experiment Station.--:- St. Paul, Minnesota.Technical Bulletin No. 136.1939.47p. 119. Neuerer, H. and K. Polina. Chemical control of undesirable pond plants with special attention to the toxicity of herbicides to fish.Pflanzenschutzber 24: 139 -162.1960. 120. Newman, J. F.The ecological effects of bipyridyl herbicides used for aquatic weed control.Proceedings European Weed Research Council International Symposium Water Weeds. Oldenburg, West Germany.1967.p. 168-174.

121. New Zealand Department of Agriculture.Very promising results in control of submerged water weeds. New Zealand Journal of Agriculture 104:26.1962.

122. Nicholson, H. P. Summary Report.Expounded project for aquatic plant control.Public Health Service. Department of Health, Education and Welfare. Region IV.Atlanta, Georgia. 1963.107p.

123. Oregon State Game Commission and Fish Commission of Oregon.Joint studies on Ten Mile Lakes. Progress Report. Salem, Oregon.1958.86p. 124. Parker, C.Influence of water hardness of phytotoxicity of paraquat.Nature 212: 1465 -1466.1966.

125. Partington, W. M.Florida Audobon's viewpoint on aquatic weed control.Hyacinth Control Journal 7:21-23.1968.

126. Patterson, W. G.The 3M concept of aquatic weed control. Proceedings 22nd Meeting Southern Weed Science Society: 324-327.1969.

127. Pearsall, W. H. and P. Ullyott.Light penetration into fresh water.III.Seasonal variations in the light conditions in Winderenere in relation to vegetation.Journal of Experimental Biology 11: 89-103.1935. 136 128. Peltier, W. H. and E. B. Welch.Factors affecting growth of rooted aquatics in a river, Weed Science 17: 412-416.1969.

129. Factors affecting growth of rooted aquatic plants in a reservoir. Weed Science 18: 7-9.1970. 130. Pennsalt Chemicals Corporation. Aquatic weed control with Aquathol.Tacoma, Washington.Bulletin A-23.1960.16p. 131. Toxicological and residue information on Aquathol.Tacoma, Washington.1961.13p. 132. Pitney, W. E. A study of Oregon's aquatic weed problems and methods for their control. Oregon Game Commission Report. Salem, Oregon.1948.37p. 133. Reimer, D. N. and S. J. Toth. A survey of the chemical composition of Potamogeton and Myriophyllum in New Jersey. Weed Science 17:219-223.1969.

134. Renard, C.The use of diquat and paraquat to control aquatic plants.2e Conference Com. Francais. Mauvaises Herbes: 9.Paris, France.1963.

135. Personal communication. Overseas Development Department, Plant Protection Limited. Fernhurst, England.1968.

136. St. John, Harold.II.Monograph of genus Elodea--summary. Rhodora 67: 155 -179.1965. 137. Saltzman, W. 0. A compilation of data from Tahkenitch Lake, Douglas County, Oregon. Oregon Game Commission Report. Salem, Oregon.1963.59p. 138. An investigation of the aquatic weed problem at Tahkenitch Lake--1964. Oregon Game Commission Report. Salem, Oregon.1964.39p.

139. A review of fishery management at Siltcoos Lake. Oregon State Game Commission Report. F-69-R -3. 1966.73p.

140. Schenk, C. F. and Jarolinek,I.Aquatic vegetation control with diquat and paraquat. Research Report, National Weed Control Committee, Eastern Section: 165 -166.1965. 137 141. Schenk, C. F. and Jarolinek, I,Experimental aquatic weed control with Aquathol/Silvex, diquat and simazine in Ontario. Abstracts 1966 Meeting Weed Society of America;St. Louis, Missouri.1966,p. 98. 142. Schomer, H. A.Photosynthesis of water plants at various depths in the lakes of Northeastern Wisconsin. Ecology 15: 217-218.1934.

143. Schulthorpe, C. D.The biology of aquatic vascular plants. St. Martins Press. New York, New York. 1967.690p. 144. Seabrook, E. L. and L. E. Scherer. The use of acrolein for the control of elodea.Hyacinth Control Journal 4:22.1965. 145. Seaman, D. E. and T. M. Thomas. Absorption of herbicides by submersed aquatic plants.Proceedings 18th Annual California Weed Conference: 11 -12,1966. 146. Sheldrick, R. D.The effect of spraying diquat in full sunlight or in darkness.Pest Articles and News Summaries 13: 316- 319.1967.

147. Springett, R. W. Dipridylium herbicides. Outlook for Agri- culture 4:226-233.1965.

148. Smith, A. E.Residues in potato tubers following haulm dessication with 14C- diquat.Bulletin of Environmental Con- tamination and Toxicology 2:169-177.1967.

149. Smith, E. V. and H. S. Swingle.The use of fertilizer for controlling several submerged aquatic plants in ponds.Trans- actions of American Fisheries Society 71:94-101.1941.

150, Smith, G. E. and B. G. Isom.Investigation of effects of large scale applications of 2, 4-D on aquatic fauna and water quality.Pesticides Monitoring Journal 1: 16 -21.1967.

151. Smith, J. M. and G. R. Sagar. A re-examination of the influence of light and darkness on the long distance transport of diquat in Lycopersicon esculentum Mill. Weed Research: 6: 314-321.1966.

1 52. Stevens, J. B.Angler success as a quality determinant of sport fishery recreational values.Transactions of American Fisheries Society 95: 357 -362.1966. 138 153. Stevens, J. B.Recreation benefits from water pollution control.Water Resources Research 2: 167 -182.1966.

154. Measurement of economic values in sport fishing.Transaction of American Fisheries Society 98: 352 - 357.1969.

155. Still, Henry.The dirty animal.Hawthorne Book Inc. New York, New York.1967.298p. 156. Stryckers, J. M. T. and J. A. Timmermans. Apercu du controle de la vegetation aquatique dans les etangs d'elevage. Proceedings European Weed Research Council International Symposium Water Weeds. Oldenburg, West Germany.1967. p. 75-83. 157. Surber, E. W. and Q. H. Pickering.Acute toxicity of endothall, diquat, dyamine, dalapon and silvex to fishes. Progressive Fish Culturist 24: 164 -171.1962.

158. Sutton, D. L. and S. W. Bingham. Some effects of simazine 14 and diquat on the movement of COor its metabolites in Myriophyllum spicatum.Proceedings2 21st Meeting Northeast Weed Control Conference 552-555.1967.

159. Suwunnamek, V. and R. R. Romanowski. The effects of arsonates and paraquat on Nutsedge (Cyperus rotundus L.) control.Weed Control Basic to Agricultural Development. Asian-Pacific Interchange: 141.1967.

160. Swann, A. A. B.Toxicology problems in the control of water weeds.Proceedings European Weed Research Council Inter- national Symposium Water Weeds. Oldenburg, West Germany. 1967.p. 161-167.

161. Tatum, W. M. and R. D. Blackburn. Preliminary study of the effects of diquat on the natural bottom fauna and plankton in two subtropical ponds.Proceedings 16th Annual Conference South- east Game Fisheries Commissioners:1-15.1962.

162. Thomas, T. M. Uptake and translocation of herbicides in submersed aquatic plants.Proceedings 9th British Weed Con- trol Conference: 398-403.1968. 139 163. Timmons, F. L.Present and future of aquatic weed control. Proceedings 16th Northeastern Weed Control Conference: 16- 21.1962.

164. A history of weed control in the United States and Canada. Weed Science 18:294-307.1970.

165. United States Department of Agriculture.The extent and cost of weed control with herbicides and an evaluation of important weeds, 1965.Agricultural Research Service. Report ARS 34-102. Washington, D. C.1968.85p. 166. United States Department of Interior.Pesticide-wildlife studies.United States Fishery and Wildlife Circular 199. Washington, D. C.1963.22p.

167. The effects of pesticides on fish and wildlife. United States Fishery and Wildlife Circular 226.Washington, D. C.1965.77p.

168. Van Bussenbach, E. J. and H. Elings.The use of dichlobenil against aquatic weeds in ditches and ponds.Proceedings European Weed Research Council International Symposium Water Weeds. Oldenburg, West Germany.1967.p. 130-137.

169. Van der Weij, H. G.Developments in aquatic weed control in the Netherlands. Symposium International sur le moyens de destruction des plants aquatiques. La Rochelle, France. 1964.p. 4. 170. Recent developments and investigations in the chemical control of aquatic weeds in the Netherlands. Proceedings 8th British Weed Control Conference:835-841. 1966.

171. Van Valin, C. C.Persistence of 2, 6 dichlorobenzonitrile in aquatic environments. Advances in Chemistry 60:271-279. 1966.

172. Walker, C. R.Aquatic weed control (1958-1962). Research Reports, North Central Weed Control Conference 1962:125- 126.1962.

173. Endothall derivatives as aquatic herbicides. Weeds 11:226-232.1963. 140

174. Walker, C. R.Dichlobenil as an aquatic herbicide in fish habitats.Weeds 12:267-269.1964.

175. Ware, F. J.The use of copper sulfate as a method of partial control of elodea (Elodea densa) in Lake Thonosasso, Florida. Hyacinth Control Journal 5:17-18.1966.

176. Ware, F. J. and J. D. Gorman. The result of selected aquatic herbicides on elodea in South Florida.Hyacinth Con- trol Journal 6: 48-50.1967.

177. Watson, G. H. and W. B. Bollen.Effect of copper sulfate weed treatment on bacteria in lake bottoms.Ecology 33: 522- 529.1952.

178. Weed Society of America.Herbicide Handbook. W. H. Humpherey Press Inc.Geneva, New York.1967.293p.

179. Westlake, D. F.The light climate for plants in rivers. British Ecological Society Symposium 6: 99-119.1966.

180. The biology of aquatic weeds in relation to their management. Proceedings 9th British Weed Control Conference:372-381.1968.

181. Whitely, James R.Diquat for control of filamentous algae and other submersed aquatic plants.Missouri Conservation Commission Report.Jefferson City, Missouri.1964.2p.

182. Personal communication. Missouri Conser- vation Commission, Columbia, Missouri.1965.

183. Wilkinson, R. E.Effects of light intensity and temperature on the growth of waterstargrass, coontail and duckweed. Weeds 11 :287 -290.1963.

184. Wilkinson, V.Ecological effects of diquat.Nature 224: 618- 619.1969.

185. Wilson, D. C.The effects of the herbicides diquat and dichlobenil on pond invertebrates.Master's thesis.Corvallis, Oregon State University.1968.74 numb. leaves.

186. Yeo, R. R.Dissipation of diquat and paraquat and effects on aquatic weeds and fish.Weeds 15: 42-45.1967. 141 187. Yeo, R. R.Dissipation of endothall and effects on aquatic weeds and fish.Weed Science 18:282-284.1970.

188. Younger, R. R.Progress report on the use of Kuron, 2, 4 -D and 2, 4, 5 -TP granules as aquatic herbicides.Proceedings 13th Northeastern Weed Control Conference: 322-323.1959. APPENDIX 142

Red

Blue 100

eu ri 0 75

....g 50 Pd

[11 25

300 400 500 600 700 Wavelength, mu

Appendix Figure 1. Transmission of visible light through four Rohm & Haas plexiglas filters.

I 143

Appendix Table 1.Chemical composition of water at Fairplay Laboratory. Range of concentration Constituents Meanconcentration1/ over 1 year Magnesium 7.8 7.6-8.0 Calcium 12.0 12.0-14.0 Sodium 7.7 7.5-8.1 Bicarbonate 79.0 77.0-80.0 Carbonate 0.0 0.0 Sulfate 5.1 4.2-5.6 Chloride 4.3 4.2-5.6 Nitrate 6.1 5.3-7.4 Iron 0.03 0.01-0.05 Hardness 64.0 62-68 Dissolved solids 132.0 131-134 pH 6.9 6.8-7.0

1/Allvalues except pH expressed as mg/l. Appendix Table 2.Preliminary evaluation of diquat and diquat combinations against four submersed hydrophytes.Laboratory Trial 1.

% control-1/ Elodea densa Elodea canadensis Ceratophyllum demersumMyriophyllum verticillatum Rate Treatment ppmw I II Mean I II Mean I II Mean I II Mean

Diquat 1.0 90 95 93 100 100 100 99 93 96 100 100 100 0. 5 85 90 88 100 9S 98 100 100 100 90 90 90 0.25 85 85 85 95 95 95 75 85 80 85 80 83 0.1 50 40 45 95 90 93 0 0 0 15 10 13

Diquat + Endothall 1.0 + 1.0 85 85 85 70 75 73 95 95 95 100 100 100 0.5 + 0.5 80 80 80 65 65 65 100 100 100 100 100 100 0.25 + 0. 25 75 75 75 70 70 70 90 80 85 95 100 98 0.1 + 0.1 60 55 58 60 70 68 10 10 10 65 70 68

Diquat + CuSO4 1.0 + O. 5 85 85 83 90 90 90 100 100 100 100 100 100 0. 5 + 0. 5 80 80 80 85 90 88 85 75 80 85 85 85 O. 25 + 0. 5 SS 60 58 80 85 83 55 65 60 70 70 70 O. 1 + O. 5 45 50 48 95 90 93 10 10 10 45 45 45

Endothall 1.0 0 0 0 0 0 0 40 35 38 30 35 33 0. 5 0 0 0 0 0 0 10 10 10 0 0 0 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0. 1 0 0 0 0 0 0 0 0 0 0 0 0

CuSO4 10.0 98 95 97 100 98 99 100 100 100 100 100 100 0.5 10 5 8 20 15 18 10 15 12 10 10 10 0.25 0 0 0 0 0 0 0 0 0 0 0 0

Control 0 0 0 0 0 0 0 0 0 0 0 0

1/ Visual evaluation of control Appendix Table 3.Preliminary evaluation of diquat and diquat combinations against four submersed hydrophytes, Laboratory Trial 1.

Length of harvested stem (centimeters) Elodea densa Elodea canadensis Ceratophyllum demersumMyriophyllum verticillatum Rate Treatment ppm I II Mean I II Mean I II Mean

Diquat 1.0 25.0 20.0 22 6.0 10.0 8 5.0 7.0 6 0.5 42.0 31.0 36 8.0 13.0 11 18.0 20.0 19 0.25 49.0 46.0 48 13.0 17.0 15 NO LENGTH 31.0 39.0 35 0.1 80.0 90.0 85 12.0 19.0 16 90.0 98.0 94 MEASUREMENT Diquat + Endothall 1.0 + 1.0 56.0 46. 0 51 39.0 39. 0 39 8. 0 4.0 6 0. 5 + 0. 5 40.0 36.0 38 57.0 46.0 52 3.0 10.0 7 TAKEN 0.25 + 0.25 44.0 41.0 42 60.0 61.0 61 14.0 5.0 9 O. 1 + O. 1 55.0 61.0 58 64.0 59.0 62 53.0 48.0 51

Diquat + CuSO4 1.0 + 0. 5 57.0 55.0 56 20.0 25.0 23 7.0 3.0 5 O. 5 + O. 5 58.0 51.0 55 26.0 25.0 26 25.0 30.0 28 0. 25 + 0. 25 60.0 58.0 59 25.0 20.0 23 48. 0 50.0 49 O. 1 + 0. 5 67.0 62. 0 65 8.0 16.0 12 77. 0 75.0 76 Endothall 1.0 100.0 100.0 100 100.0 100.0 100 91.0 85.0 88 0. 5 100.0 100. 0 100 100.0 100.0 100 98.0 100.0 99 0.25 100.0 100.0 100 100.0 100.0 100 100.0 97.0 98 0. 1 100.0 100.0 100 100.0 100.0 100 100.0 100.0 100

CuSO4 10.0 11.0 13.0 12 3.0 25.0 14 93.0 95.0 94 0.5 100.0 100.0 100 85.0 90.0 88 100.0 100.0 100 0.25 100.0 100.0 100 100.0 100.0 100 100.0 100.0 100 Control 100.0 100.0 100 100.0 100.0 100 100.0 100.0 100 Appendix Table 4.Preliminary evaluation of diquat and diquat combinations against four submersed hydrophytes, Laboratory Trial 1.

Dry weight of harvested stem (milligrams)1/ Elodea dens a Elodea canadensis Ceratophyllum demersumMyriophyllum verticillatum Rate Treatment ppm I II Mean I II Mean I II Mean I II Mean

Diquat 1.0 300 320 310 12 14 13 121 101 111 33 45 39 0.5 460 500 480 23 38 30 21 55 38 245 335 290 0.25 480 690 585 63 67 65 508 496 502 507 450 479 0.1 890 720 805 56 65 61 1695 1381 1538 1349 1240 1295 Diquat + Endothall 1.0 + 1.0 610 525 567 203 131 167 113 108 111 25 22 24 0.5 + 0.5 450 489 470 225 151 187 97 61 79 19 22 21 0.25 + 0.25 310 392 351 302 181 242 232 278 255 22 19 21 0.1 + 0.1 656 700 676 388 191 289 1228 1170 1199 209 168 189

Diquat + CuSO4 1.0 + 0.5 590 542 566 61 42 52 75 91 84 15 10 13 0.5 + 0.5 570 431 500 141 135 138 312 427 370 401 480 441 0.25 + 0.5 820 732 776 174 82 128 516 590 553 722 675 699 0.1 + 0.5 660 509 584 85 68 77 1291 1081 1186 1020 1071 1046 Endothall 1.0 2010 2250 2130 312 440 376 824 930 877 659 770 715 0.5 2030 1747 1890 375 286 331 1116 1125 1120 1117 1091 1004 0.25 1600 1524 1562 355 474 415 1595 1322 1458 1051 1022 1037 0.1 2250 2102 2180 390 577 484 1624 2127 1875 998 1062 1032

CuSO 10.0 100 205 152 18 24 21 22 39 31 30 36 33 4 0.5 2380 2012 2196 246 350 298 992 1021 1007 940 981 961 0.25 2460 1632 2046 353 444 398 1599 1603 1601 1223 1345 1284

Control 1660 2321 1990 314 389 366 1181 1482 1332 1278 1025 1152

1/ 15 gms fresh weight per plot except E. canadensis 5.00 gm fresh weight. Appendix Table 5.The effect of time of application on the activity of diquat and diquat combinations againstE. densa asestimated by dry weight of stem, Laboratory Trial 2.

Dry weight stem (milligrams) Beginning Light Rate Middle Light Beginning Dark Middle Dark Treatment ppm I II III IV Mean I II III IV Mean I II III IV Mean I II III IV Mean

Diquat 0. 5 96 33 99 80 77.0 64 59 92 80 73.75 15 21 22 90 37.0 140 74 136 68 104.5 Diquat 0.25 145 148 188 176 164.25 95 73 69 76 78.25 495 389 390 423 424.25 427 451 352 425 413.75 Diquat + CuSO4 0. 25+0.5 165 155 150 96 141.5 84 91 76 48 74. 75 524 458 366 404 438.0 224 202 115 309 212. 5 CuSO4 0.5 1205 1321 1234 1352 1278.0 1755 1479 1224 1970 1607.0 1704 1518 1486 1409 1529.25 1628 1302 1551 1442 1480.75 Control 1347 1325 1423 1489 1396.0 1523 1493 1583 1323 1480.5 1527 1409 1446 1426 1452.0 1514 1348 1625 1582 1517.25

Appendix Table 6.The effect of time of application on the activity of diquat and diquat combinations against E. densa as estimated by visual evaluation of control,Laboratory Trial 2.

% Control1/

Rate Beginning Light Middle Light Beginning Dark Middle Dark Treatment ppm I II III IV Mean I II III IV Mean I II III IV Mean I II III IV Mean

Diquat 0. 5 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 98 100 98 100 99 Diquat 0. 25 98 98 98 98 98 100 100 100 100 100 75 80 80 85 80 70 75 75 75 74 Diquat + CuSO4 0. 25+0. 5 100 98 98 100 99 100 100 100 100 100 70 70 70 70 70 80 95 95 95 89 CuSO4 0. 5 5 15 10 10 10 0 0 10 0 2 0 0 5 5 2 0 5 0 10 4 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1/ Visual evaluation of control Appendix Table 7.The effect of time of application on the activity of diquat and diquat combinations against E. dersaas estimated by stem length, Laboratory Trial 2.

Harvested stem length (centimeters)

Rate Beginning Light Middle Light Beginning Dark Middle Dark Treatment ppm I II III Mean N I II III IV Mean I II III IV Mean I II III IV Mean Diquat 0.5 8.0 7.0 12.0 9.0 9.0 9.0 7.0 10.0 11.0 9.2 4.0 5.0 7.0 12.0 7.0 13.0 9.0 13.0 10.0 11.2 Diquat 0.25 18.0 13.0 19.0 17.0 16.8 10.0 12.0 4.0 9.0 8.2 25.0 34.0 29.0 28.0 29.0 46.0 40.0 40.0 39.0 41.2 Diquat + CuSO4 0. 25+0.5 8.0 16.0 14.0 8.0 11.5 11.0 9.0 6.0 6.0 8.0 37.047.0 33.0 44.0 40.2 29.020.0 20.0 28.0 24.2 CuSO4 0.5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0100.0100.0100.0100.0 100.0100.0 100.0 Control 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0100.0100.0100.0100.0 100.0100.0 100.0 149

Appendix Table 8.Analysis of variance for the time of application trial, Laboratory Trial 3.

MS F LSD LSD Source of variation df SS 0.05 0.01 a) DRY WEIGHT

REPS 3 54576. 14 18192. 05 2. 69NS LITE 3 342386. 34 114128. 78 16. 89** 58. 1 mg 84. 7 mg L x R (Error a) 9 60794. 11 6754. 90 CHEM 4 31838485. 92 7959621. 48 793. 6** 71. 5 mg 95.6 mg L x C 12 603859. 98 50321. 66 5.02 ** 143. 0 mg 191. 2 mg CxLxRiC x R (Error b) 48 493336. 50 10029. 35 TOTAL 79 CVError =11.7% CV = 14.3% a Error b b) STEM LENGTH

REPS 3 11.04 3.68 O. 3ONS LITE 3 1661. 74 553. 91 45. 40** 2. 99 cm 3. 38 cm L x R (Error a) 9 109. 81 12. 20 CHEM 4 131003. 50 32750. 87 4554. 01** 1. 19 cm 2.65 cm L x C 12 3366. 70 280. 56 39. 02** 3. 99 cm 5. 11 cm CxR 13 (Error b) Cx L x 48 345. 40 7. 19 CVError = 6. 9% CVError = 5. 3% a b c) % CONTROL (ARCSIN transformation)

REPS 3 102.02 34.01 1. 59NS LITE 3 2425. 16 808. 39 37.8** 0. 4 0. 7 L x R (Error a) 9 192. 51 21. 39 CHEM 4 110576. 04 27644. 01 1773. 2** 0.3 0. 4 L x C 12 3397. 87 283. 16 18.2** 0. 9 2.0 CxR 1(Error b) L x C x R 48 748. 20 15. 59 CVError = 9. 3% CVError = 7. 9% a b

**Significant at 0.01 level. 150 Appendix Table 9.Effect of length of exposure on diquat and diquat combination activity on E. densa at 10°C as estimated by dry weight of stem, Laboratory Trial 3. Dry weight stem (milligrams) Hours exposure I II III Mean

Diquat 0.025 ppmw 0 1266 1431 1394 1363. 7 2 480 547 613 546.7 6 323 310 356 329.7 12 201 235 240 225.3 24 109 46 56 70.3 48 85 48 74 69.0 720 90 76 68 78.0 Diquat + Endothall 0.25 + 0.25 ppmw 0 1487 1443 1283 1397. 7 2 667 645 623 643.3 6 535 523 591 549.7 12 430 321 393 381.3 24 252 125 134 170.3 48 101 100 89 96.7 720 85 71 76 77.3

ANOVA Source of variation df SS MS F LSD0_ 05 LSDO01

REPS 2 981.0 490.5 0.07 CHEM 1 86042. 88 86042. 88 12. 77NS CHEM x REPS (Error a) 2 13475. 19 6737. 59 EXPO 6 7726027.0 1287671. 16 567. 5** 56.8 mg 76.9 mg EXPO x CHEM 6 54960. 62 9160. 10 4. 04** EXPO x REPS (Error b) ExCxR 24 54457. 8 2269. 1 CVError = 11.1% b **Significant at 0.01 level. 151 Appendix Table 10.Effect of length of exposure on diquat and diquat combination activity against E. densa at 10°C as estimated by visual evaluation, Laboratory Trial 3.

Hours %controll/ exposure I II III Mean

Diquat 0.25 pprnw 0 0 0 0 0 2 25 45 45 36 6 75 70 75 73 12 85 80 80 82 24 95 98 100 98 48 100 98 100 99 720 100 100 100 100 Diquat + Endothall 0.25 + 0.25 ppm 0 0 0 0 0 2 30 20 15 22 6 60 65 60 62 12 65 75 65 68 24 90 85 85 87 48 90 95 98 94 720 100 100 100 100

1Visualevaluation of control.

ANOVA Source of variation df SS MS REPS 2 9.14 4.57 0.22 CHEM 1 712.59 712.59 34.47* CHEM x REPS (Error a) 2 41. 33 20.67 EXPO 6 51159. 62 8526.60 397.9 ** EXPO x CHEM 6 393. 90 65.65 3.06* EXPO x (Error b) ExCxR 24 514.19 21.43 CVError = 6. 9 % CVError = 7. 1% a b *Significant at 0.05 level. **Significant at 0.01 level. 152 Appendix Table 11.Effect of length of exposure on diquat and diquat combination activity against E. densa at 10°C as estimated by length of stem harvested, Labora- tory Trial 3, Stem length (centimeters) Hours exposure I II III Mean

Diquat 0,25 ppmw 0 100 100 100 100.0 2 74 64 68 66.7 6 34 40 33 35.7 12 22 25 28 25.0 24 14 12 8 11.3 48 10 12 10 10.7 720 12 10 10 10.7 Diquat + Endothall 0.25 + 0.25 ppmw 0 100 100 100 100.0 2 70 77 90 79.0 6 58 50 57 55.0 12 48 35 44 42.3 24 19 21 22 20.7 48 17 15 13 15.0 720 9 11 9 9.7

ANOVA Source of variation df SS MS F

REPS 2 15. 47 7. 73 0. 40 CHEM 1 762. 88 762. 88 39. 22* CHEM x REPS (Error a) 2 38. 90 19. 45 EXPO 6 41983. 81 6997.30 404. 7** EXPO x CHEM 6 568. 95 94. 83 54. 8' EXPO x REPS j(Error b) ExCxR 24 414. 95 17. 29 CV = 10. 6% CV = 10.0% a Error b *Significant at 0.05 level. **Significant at 0.01 level. 153 Appendix Table 12.Effect of length of exposure on diquat and diquat combination activity on E. densa at 20°C as estimated by dry weight of stem, Laboratory Trial 3. Stem dry weight (milligrams) Hours exposure I II III Mean Diquat 0.25 ppmw 0 1462 1408 1480 1450. 0 2 365 362 419 382.0 6 280 251 301 277.3 12 206 217 229 217.3 24 92 101 122 105.0 48 99 134 62 98.3 500 79 108 63 99.3 Diquat + Endothall 0. 25 + O. 25 ppmw 0 1323 1338 1475 1378.7 2 322 365 362 349.7 6 223 303 249 258.3 12 144 171 121 145.3 24 146 65 88 99.7 48 48 56 94 66.0 500 100 106 92 99.3

ANOVA Source of variation df SS MS F LSD0.05 LSD0.01

REPS 2 2633.90 1316. 95 6.49NS CHEM 1 10028.59 10028. 59 49. 41* CHEM x REPS (Error a) 2 405.90 202. 95 EXPO 6 8206818.57 1367803. 09 102.5** 43.6 mg 59.0 mg EXPO x CHEM 6 9484.57 1580. 76 1. 2NS EXPO x REP1 b) ExCxR 24 32018.86 1334. 1 CVError = 11.3% b *Significant at 0.05 level. **Significant at 0.01 level. 154 Appendix Table 13.Effect of exposure time on diquat and diquat combination activity on E. densa at 20°C as estimated by visual evaluation, Laboratory Trial 3. / Hours %Controll exposure I II III Mean

Diquat 0.25 ppmw 0 0 0 0 0 2 65 65 70 67 6 80 75 75 77 12 90 85 85 87 24 100 100 98 99 48 100 100 100 100 500 100 100 100 100 Diquat + Endothall 0.25 + 0.25 ppmw 0 0 0 0 0 2 65 60 70 65 6 80 80 80 80 12 90 90 90 90 24 95 100 98 98 48 100 100 100 100 500 100 100 100 100

1Visualestimation.

ANOVA (ARCSIN transformation) Source of variation df SS MS

REPS 2 1. 94 0. 97 0. 1 CHEM 1 0.002 0. 002 0. 0003NS CHEM x REPS (Error a) 2 17. 92 8. 96 EXPO 6 36160. 18 6026.69 93. 71** EXPO x CHEM 6 49. 78 8. 30 1. 29NS EXPO x REPS.} (Error b) E x C x R 24 154.39 6. 43

CV = 4. 4% Error b **Significant at 0.01 level. 155 Appendix Table 14.Effect of length of exposure on diquat and diquat combination activity on E. densa at20°Cas estimated by stem length, Laboratory Trial 3. Stem length (centimeters) Hours exposure I II III Mean Diquat 0.25 ppmw 0 100 100 100 100.0 2 48 48 45 47.0 6 28 35 33 32.0 12 18 24 24 22.0 24 10 9 14 11.0 48 11 8 10 9. 7 500 9 9 14 9.3 Diquat + Endothall 0.25 + 0.25 ppmw 0 100 100 100 100.0 2 41 46 38 41.7 6 31 27 27 28.3 12 18 20 21 19.7 24 16 12 14 14.0 48 4 11 10 8.3 500 11 12 7 10.0

ANO VA Source of variation df SS MS F

REPS 2 9. 14 4. 57 0. 84 CHEM 1 17. 36 17. 35 3. 19NS CHEM x REPS (Error a) 2 10. 86 5. 43 EXPO 6 37867. 81 6311.30 993.8 ** EXPO x CHEM 6 70. 48 11. 75 1. 85NS EXPO x REPS] (Error b) CxExR 24 154.00 6.35 CV = 8.6% b **Significant at 0.01 level. 156 Appendix Table 15.Effect of length of exposure on diquat and diquat combination activity against E. densa at 30°C as estimated by stem dry weight, Laboratory Trial 3. Stem dry weight (milligrams) Hours exposure I II III Mean

Diquat 0,25 ppm 0 1420 1462 1444 1442. 0 2 564 606 644 604. 7 6 42 72 138 84.0 12 22 98 35 51.7 24 101 32 52 61. 7 48 30 13 32 25.0 360 13 32 28 24.3 Diquat + Endothall 0.25 + 0.25 ppm 0 1645 1431 1366 1480. 7 2 106 100 111 105.7 6 202 143 253 199.3 12 25 52 11 29.3 24 10 38 26 24.7 48 65 26 26 39.0 360 79 13 28 40.0

ANOVA df SS MS F LSD LSD Source of variation 0, 05 0. 01

REPS 2 1550.29 775.14 O. 14NS CHEM 1 30080. 38 30080. 38 5. 64NS CHEM x REPS (Error a) 2 10655. 90 5332. 95 EXPO 6 9921990. 47 1653665. 08 704. 2** 57.6 mg 78.0. mg EXPO x CHEM 6 369080. 28 61513. 38 26. 2** 81.5 mg 110.5 mg EXPO x REPS/ (Error b) ExCxR 24 56355. 70 2348. 10 TOTAL 41 CVError = 17.6% b **Significant at 0.01 level. 157 Appendix Table 16.Effect of exposure time on diquat and diquat combination activity against E. densa at 30°Cas estimated by visual evluation, Laboratory Trial 3.

Hours %Control1/ exposure I II III Mean Diquat 0.25 ppm 0 0 0 0 0 2 70 65 65 67 6 100 100 100 100 12 100 100 100 100 24 100 100 100 100 48 100 100 100 100 360 100 100 100 100 Diquat + Endothall 0.25 + 0.25 0 0 0 0 0 2 98 98 98 98 6 98 98 98 98 12 100 100 100 100 24 100 100 100 100 48 100 100 100 100 360 100 100 100 100

1/Visual estimation of control.

ANOVA (ARCSIN transformation) Source of variation df SS MS

REPS 2 0.45 0.229 1. 03NS CHEM 1 77.28 77.28 346. 5** CHEM x REPS (Error a) 2 0. 446 0. 223 EXPO 6 40028. 02 6671. 34 33356.0** EXPO x CHEM 6 1125. 11 187. 52 841.3** EXPO x REPS, b) ExCxR 24 5. 34 0.2229 CV = 0.71% Error a and b

**Significant at 0.01 level. 158 Appendix Table 17.Effect of length of exposure on diquat and a diquat combination activity against E. densa at 30°C as estimated by stem length, Laboratory Trial 3. Stem length (centimeters) Hours exposure I II III Mean

Diquat 0.25 ppm 0 100 100 100 100.0 2 37 46 46 43. 0 6 6 7 9 7.3 12 4 3 4 3.7 24 3 3 4 3. 3 48 3 3 2 2.7 360 3 4 4 3.7 Diquat + Endothall 0.25 + 0.25 ppm 0 100 100 100 100.0 2 10 12 9 10.3 6 11 11 13 11.7 12 2 3 2 2.3 24 2 3 4 3.0 48 5 3 2 3.3 360 4 3 2 3.0

ANOVA Source of variation df SS MS

REPS 2 5. 76 0. 708 0. 708 CHEM 1 192.85 192.85 47. 39* CHEM x REPS (Error a) 2 8. 14 4. 07 EXPO 6 46098. 62 7683. 10 2877. 1** EXPO x CHEM 6 1440. 14 240.02 89. 88** EXPO x REPS.) (Error b) ExCxR 24 64.09 2.67 TOTAL 41 CVError= 9.5%CVError = 7.6% a b *Significant at 0. 05 level. **Significant at 0.01 level. Appendix Table 18.Effect of light quality on the activity of diquat and diquat combinations on E. densa at 10, 20 and 30°C as estimated by dry weightof stem, Laboratory Trial 4.

Stem dry weight (milligrams) 10 °C 20°C 30°C Rate Treatment ppm I II III IV Mean I II III IV Mean I II III IV Mean

CLEAR LIGHT Diquat 0. 5 329 463 431 362 396. 25 424 420 391 425 419. 5 532 530 552 506 530.0 Diquat 0.25 125 245 130 202 175.5 610 492 430 536 517.0 771 603 638 605 654.25 Diquat + CuSO4 0. 25 + 0. 5 482 350 321 334 371. 75 651 532 502 539 556.0 582 587 623 591 595. 75 Diquat + Endothall 0. 25 + 0.25 461 385 301 292 359. 75 382 331 322 345 355.0 372 302 382 342 349. 5 Endothall 0.25 1351 1242 1303 1291 1296.75 1375 1248 1199 1233 1263.751556 1245 1752 1612 1541.25 CuSO4 0.5 1145 1094 1011 1201 1112.75 1334 935 945 1113 1081.751142 999 1043 1135 1092.25 Control 1717 1728 1622 1601 1667.0 1452 1420 1310 1089 1317.751205 1553 1225 1513 1374.0 RED LIGHT Diquat 0.5 225 320 292 283 280.0 419 490 363 453 431.25308 293 321 272 298.5 Diquat 0.25 315 304 302 321 310.5 565 550 399 401 478.75362 393 389 332 369.0 Diquat + CuSO4 0. 25 + 0. 5 373 425 461 390 412. 25 652 601 506 525 571.0 513 692 532 633 592. 0 Diquat + Endothall 0. 25 + 0. 25 638 597 589 499 580. 75 910 893 1194 745. 935. 5 234 305 302 282 280. 75 Endothall 0.25 1286 1754 1201 1398 1409.75 1555 1269 1307 1286 1354.251303 1342 1142 1369 1289.0 CuSO4 0.5 1175 1017 1202 1131 1131.25 1085 1092 1034 1150 1090.251027 934 1120 1017 1023.0 Control 1717 1375 1272 1326 1422.5 1150 1145 1269 1301 1216.251356 1413 1127 1307 1300.75 GREEN LIGHT Diquat 0.5 188 112 171 99 142.5 429 385 565 376 438.75427 446 437 521 457.75 Diquat 0.25 221 286 201 222 232.5 422 446 542 373 445.75605 527 632 705 617.25 Diquat + CuSO4 O. 25 + 0. 5 316 532 467 482 449. 25 831 767 786 767 783.25782 815 842 846 821. 25 Diquat + Endothall 0. 25 + 0.25 760 500 701 602 640. 75 521 463 431 492 476. 75406 267 291 372 334. 0 Endothall 0.25 1252 1250 1591 1321 1353.5 1392 1288 1342 1230 1313.01649 1585 1557 1782 1643.25 CuSO4 0.5 1005 1074 1102 1074 1063.75 1382 1179 1313 982 1214.01164 1149 1007 1178 1124.5 Control 1299 1258 1332 1381 1317.5 1562 1423 1290 1429 1426.01347 1207 1278 1389 1305.25 BLUE LIGHT Diquat 0.5 100 130 147 113 122.5 392 375 385 389 385.25352 332 292 401 344.25 Diquat 0. 25 263 234 291 300 272. 0 540 502 382 322 437. 75468 509 405 558 485.0 Diquat + CuSO4 0.25 +0.5 115 68 117 100 100.0 659 694 730 502 646.25612 682 705 739 684. 5 Diquat + Endothall 0. 25 + 0. 25 231 229 214 200 218.5 512 509 522 472 503. 75207 403 279 331 305.0 Endothall 0.25 1439 976 1004 1362 1195.25 1432 1025 1102 1356 1228.751603 1827 1405 1362 1549.25 CuSO4 0.5 1028 987 905 992 978.0 1285 1315 1192 1086 1219.5 943 1144 1142 1182 1102.75 Control 1878 1505 1321 1423 1531.75 1405 1312 1338 1283 1334.51327 1841 1621 1721 1652.5 Appendix Table 19.Effect of light quality on the activity of diquat and diquat combinations on E. densa at 10, 20 and 30°C as estimated by visual evaluationof control, Laboratory Trial 4. 1/ % Control- 10°C 20°C Rate 30°C Treatment ppm I U III IV Mean I II III IV Mean I II III IV Mean

CLEAR LIGHT Diquat 0.5 85 80 85 80 82.5 80 80 80 80 80.0 80 85 90 90 86.25 Diquat 0.25 90 85 90 90 88.75 80 75 75 75 76.25 60 65 65 65 63.75 Diquat + CuSO4 0. 25 + 0.5 85 80 80 80 81.25 75 70 70 70 71. 25 60 70 65 60 63.75 Diquat + Endothall 0. 25 + 0.25 85 80 85 85 83. 75 90 85 85 90 87.5 90 90 90 90 90.0 Endothall 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0. 5 10 10 10 10 10.0 5 5 10 5 6.25 10 10 10 5 8.75 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 RED LIGHT Diquat 0.5 90 85 85 85 86.25 90 85 90 95 87.5 90 80 85 85 85.0 Diquat 0.25 80 80 80 80 80.0 85 85 90 90 87.5 80 85 80 75 80.0 Diquat + CuSO4 0. 25 + 0. 5 80 80 80 80 80.0 70 70 75 70 73. 5 75 80 75 75 76. 25 Diquat + Endothall 0. 25 + 0.25 75 75 75 75 75.0 65 65 60 60 62. 5 90 90 95 85 90.0 Endothall 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0.5 15 10 10 10 11.25 5 5 10 5 7.5 10 10 5 5 7.5 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 GREEN LIGHT Diquat 0.5 100 100 100 100 100 80 85 80 85 82.5 90 85 85 80 85.0 Diquat 0.25 90 85 90 90 88.75 85 85 85 85 85.0 80 85 80 80 81.25 Diquat + CuSO4 O. 25 +0.5 80 80 80 80 80.0 65 65 70 75 68. 5 65 60 65 50 60.0 Diquat + Endothall 0. 25 + 0.25 80 75 75 75 76. 25 80 80 85 85 82. 5 90 85 95 95 91.25 Endothall 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0.5 10 15 10 10 11.25 5 5 5 5 5.0 10 10 10 10 10.0 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 BLUE LIGHT Diquat 0. 5 100 100 100 100 100.0 80 85 80 90 83. 5 80 90 90 90 87. 5 Diquat 0. 25 90 85 90 90 88. 75 85 80 85 85 83.75 70 75 70 75 72. 5 Diquat + CuSO4 0. 25 + 0. 5 98 98 98 98 98.0 60 65 65 75 66.25 85 80 75 70 77. 5 Diquat + Endothall 0. 25 + 0.25 90 90 90 90 90.0 80 85 85 90 85.0 90 90 90 90 90.0 Endothall 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0.5 10 15 10 10 11.25 5 5 5 5 5.0 5 10 15 10 10.0 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1/ Visual evaluation of control Appendix Table 20.Effect of light quality on the activity of diquat and diquat combinations on E. densa at 10, 20 and 30°C as estimated by length ofstem, Laboratory Trial 4.

Length of stem (cm)

10°C 20°C 30°C Rate Treatment ppm I II III IV Mean I II III IV Mean I II III IV Mean

CLEAR LIGHT Diquat 0.5 30 35 31 34 32.5 50 SS 48 49 SO. 5 49 40 40 42 42.75 Diquat 0.25 20 24 22 22 22.0 50 55 56 60 55.25 70 66 61 54 62.75 Diquat + CuSO4 0. 25 + 0. 5 28 34 30 30 30.5 52 55 58 53. 55.75 65 64 61 60 62. 5 Diquat + Endothall 0. 25 + 0.25 26 29 27 27 27. 25 36 36 33 42 36. 75 30 34 35 35 33. 5 Endothall 0. 25 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 CuSO4 0. 5 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Control 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 RED LIGHT Diquat 0.5 20 26 22 24 23.0 32 35 31 32 32.5 30 40 36 39 36.25 Diquat 0.25 35 35 36 34 35.0 43 43 32 31 37.25 57 55 59 54 56.25 Diquat + CuSO4 0. 25 + 0. 5 38 32 34 36 35.0 60 58 51 42 52. 75 54 54 59 60 57. 5 Diquat + Endothall 0. 2S + 0.25 42 43 40 44 42. 25 60 60 68 65 63.25 31 34 37 35 34. 25 Endothall 0. 25 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 CuSO4 0. 5 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Control 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 GREEN LIGHT Diquat 0.5 10 11 9 8 9.5 45 38 47 39 42.25 40 45 44 46 43.75 Diquat 0.25 22 27 23 21 23.25 38 36 39 34 36.75 48 45 50 50 48.25 Diquat + CuSO4 0. 25 + 0. 5 31 33 30 32 31.5 68 65 62 65 65.0 68 67 61 62 64. 5 Diquat + Endothall 0. 25 + 0.25 35 39 36 38 37.0 45 47 44 40 44.0 38 29 28 27 30. 5 Endothall 0. 25 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 CuSO4 0. 5 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Control 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

BLUE LIGHT Diquat 0.5 8 10 9 9 9.0 46 42 45 38 42.75 39 45 40 42 41.5 Diquat 0.25 23 25 20 23 22.75 43 50 42 46 45.25 58 54 52 56 55.0 Diquat + CuSO4 0. 25 + 0. 5 14 13 13 15 13.75 61 68 67 67 65. 75 43 45 48 52 47. 0 Diquat + Endothall 0. 25 + 0.25 22 22 23 20 21. 75 45 47 40 40 43.0 30 26 29 34 29. 75 Endothall 0.25 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 CuSO4 0. 5 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Control 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 162

Appendix Table 21.Analysis of variance for the light quality/10°C trial, Laboratory Trial 4.

Source of variation df SS MS F LSD LSD 0.05 0.01 a)STEM DRY WEIGHT

REPS 3 41285. 67 13752. 89 0. 96NS QUAL 3 427384. 61 142461. 54 9. 91** 102.1 mg 187.5 mg R x Q (Error a) 9 129350. 64 14372. 30 CHEM 6 27841114. 59 4640185. 76 427. 4** 90.0 mg 136. 4 mg C x Q 18 998587. 27 55477. 07 5. 11** 154. 4 mg 211.5 mg C x R 4 rror(E b) Q x C x 72 792550. 14 10857. 4 TOTAL 111 C V = 16.2% CVError = 14.2% a b b)STEM LENGTH

REPS 3 26.79 8.93 4.88* QUAL 3 1373.0 457.67 250. 1** R x Q (Error a) 9 16. 5 1. 83 CHEM 6 151733. 48 25288. 91 14127.0 C x Q 18 2747. 87 8. 93 4. 99** C x R i(Errorb) QxCx 72 119. 21 1. 79 CV = 2.3% a c)CONTROL (ARCSINE transformation)

REPS 3 14.63 4.88 3. 13NS QUAL 3 1144. 42 381. 47 244. 5** R x Q (Error a) 9 14.03 1. 56 CHEM 6 116548. 18 19424. 69 9712. 3** C x Q 18 2508.01 139. 33 69. 6** C x R (Error b) 22cC x 72 115. 28 2.00 C V = 3. 2% a

*Significant at 0.05 level. **Significant at 0.01 level. 163

Appendix Table 22.Analysis of variance for the lightquality/20°C trial, Laboratory Trial 4.

LSD Source of variation df SS MS F LSD0.05 0.01

a)STEM DRY WEIGHT

REPS 3 109562. 67 63620. 89 12. 04** QUAL 3 135112. 59 45037. 53 8. 53** 61, 7 mg 113. 3 mg R x Q (Error a) 9 47494. 65 5277. 18 79. 5 CHEM 6 15395996.0 2565999.3 303.0** 120. 5 mg Q x C 1E; 981899. 71 54549. 98 6. 44** 136.8 mg 187. 4 mg C x R Error b) QxCx.1 72 640495. 42 8467. 19 TOTAL 111 CVError = 8. 7% CVError = 10. 9% a b

b) STEM LENGTH (cm)

REPS 3 33.67 11.22 O. 79NS QUAL 3 66. 59 22. 19 1. 77NS R x Q (Error a) 9 112.65 12. 51 CHEM 6 77172. 87 12862. 14 1838. 1** Q x C 18 3578. 34 198. 79 27.6'* C x R ( Err or b) 9xCx111.: 72 651.92 7.2 CV = 5.6% a

c) CONTROL (ARCSINtransformation)

REPS 3 51.25 19.08 3. 57NS QUAL 3 1. 19 0. 39 . 07NS R x Q (Error a) 9 48. 01 5. 33 CHEM 6 97585. 68 16264. 28 3633.0** Q x C 18 1088.21 60. 46 13. 5** C x RIkError b) QxCx 72 272.25 4. 47 CV = 13.9% a

**Significant at 0.01 level. 164

Appendix Table 23. Analysis of variance for the lightquality/30°C trial, Laboratory Trial 4.

LSD LSD Source of variation df SS MS F 0.05 0.01

a) STEM DRY WEIGHT

REPS 3 56941, 42 18980. 47 0. 96NS QUAL 3 469977. 21 156659. 07 7. 92** 119.6 mg 219.6 mg R x Q (Error a) 9 178076. 36 19786. 26 CHEM 6 22544207. 98 3757367. 99 414, 3** 82. 2 mg 124. 6 mg Q x C 18 648294. 16 36016. 34 3. 97** C x Rr(Error b) Q x C x 72 684356. 71 9068. 46 TOTAL 111 CVError = 16.6% CVError = 22. 4% a b

b) STEM LENGTH (cm)

REPS 3 3. 50 1. 17 0. 12NS QUAL 3 231. 92 77. 31 7. 60** R x Q (Error a) 9 91. 43 10. 16 CHEM 6 85361. 37 14226. 89 2215.04* Q x C 18 1118.69 62. 15 9. 74* C x R kErrorb) QxCx R 72 523.07 6. 42 C V = 4.6% a

c) % CONTROL (ARCSIN transformation)

REPS 3 33.21 11.07 2. 27NS QUAL 3 101.46 33.82 6.95 ** R x Q (Error a) 9 43. 77 4. 86 CHEM 6 99178. 12 16529. 69 2357. 0** Q x C 18 639. 85 35. 55 5. 1** C x R Ri (Error b) 2cC x 72 502.07 7.01 CV = 5. 7% a

**Significant at 0.01 level. Appendix Table 24.The effect of temperature differential on activity of diquat and diquat combinationonE. densaat 10 days after treatment, Laboratory Trial 4.

°A Control-1 30°C 10oc Rate 20°C Treatment ppm I II III IV Mean I II III IV Mean I II III IV Mean CLEAR LIGHT Diquat 0. 5 80 85 90 90 86. 25 10 20 10 15 13. 75 0 0 0 0 0 Diquat 0.25 60 65 65 65 63.75 10 5 10 15 10.0 0 0 0 0 0 Diquat + CuSO4 0. 25 + 0.5 60 70 65 60 63. 75 30 25 35 30 30.0 0 0 0 0 0 Diquat + Endothall 0. 252 90 90 90 80 90.0 20 20 15 25 20.0 0 0 0 0 0 Endothall 0. 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0.5 10 10 10 5 8.75 0 0 0 0 0 0 0 0 0 0 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 RED LIGHT Diquat 0.5 90 80 85 85 85.0 20 25 20 20 21.25 0 0 0 0 0 Diquat 0.25 80 85 80 75 80.0 20 15 20 20 18.75 0 0 0 0 0 Diquat + CuSO4 0. 25 + 0.5 75 80 75 75 76. 25 40 45 40 50 43. 75 0 0 0 0 0 Diquat + Endothall 0. 252 90 90 95 85 90.0 35 30 30 35 32. 25 0 0 0 0 0 Endothall 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0. 5 10 10 5 5 7. 5 0 0 0 0 0 0 0 0 0 0 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 GREEN LIGHT Diquat 0.5 90 85 85 80 85.0 10 15 10 10 11.25 0 0 0 0 0 Diquat 0.25 80 85 80 80 81.25 20 10 15 10 13.75 0 0 0 0 0 Diquat -I- CuSO4 0. 25 + 0.5 65 60 65 50 60.0 30 35 30 25 30.0 0 0 0 0 0 Diquat + Endothall 0. 252 90 85 95 95 91. 25 25 20 25 25 23. 75 0 0 0 0 0 Endothall 0. 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0. 5 10 10 10 10 10.0 0 0 0 0 0 0 0 0 0 0 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 BLUE LIGHT Diquat 0.5 80 90 90 90 87.5 10 20 15 20 16.25 0 0 0 0 0 Diquat 0. 25 70 75 70 75 72. 5 10 5 5 15 8. 75 0 0 0 0 0 Diquat + CuSO4 0. 25 + 0.5 85 80 75 70 77. 5 30 35 25 30 30.0 0 0 0 0 0 Diquat + Endothall 0. 252 90 90 90 90 90.0 35 30 25 30 30.0 0 0 0 0 0 Endothall 0. 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CuSO4 0.5 5 10 5 10 10.0 0 0 0 0 0 0 0 0 0 0 Control 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 Visualestimation. 166

Appendix Table 28.Results of analysis for diquatcation in samples of E. densa from Field Trial 2.

Diquatcation ppmw Date Plot Rate after Corrected Check Recovery Fortified no. Treatment ppmw treatment absorbance Found corrected corrected recovery (%)

1 Diquat 1.0 7 days 0.420 7.98 7.98 9.42

7 II 2 Diquat 0. 5 0.318 6.04 6.04 7. 13

3 Diquat 0. 25 7 " 0.225 4.28 4. 28 5.05

4 Diquat + 0. 5 + 7 II 0.324 3.82 3. 82 4. 51 CuSO4 0.5

5 Diquat + 0. 25 + 7 " 0.228 4. 33 4. 33 5. 11 CuSO4 0. 5

6 Diquat + 0. 5 + 7li 0.258 4. 90 4. 90 5. 78 Endothall 0.5

7 Diquat + 0. 25 + 7 " 0.195 3.70 3. 70 4. 37 Endothall 0.25

1 Diquat 1.0 14 days 0. 507 9.63 9.63 11. 36

2 Diquat 0.5 14 " 0.348 6.61 6.61 7.80

3 Diquat 0. 25 14 " 0.240 4. 56 4.56 5. 38

4 Diquat + 0. 5 + 14 " 0.300 5.70 5.70 6.73 CuSO4 0.5

5 Diquat + 0.25 + 14 " 0. 138 2.62 2.62 3.09 CuSO4 0. 5

6 Diquat + 0. 5 + 14 " 0.270 8. 13 5. 13 6.08 Endothall 0. 5

7 Diquat + 0.25 + 14 " 0.165 3.14 3. 14 3. 71 Endothall 0.25

Fortified check Diquat 1 0.043 0.83 0.83 1.00 83 Check 0.000 0.000 Standard check Diquat 1 0.120 1.00 1.00 167

Appendix Table 25.Visual evaluation of control of E. canadensis, by diquat and diquat combinations, Investigatory Trial 1, 1968. % plant control at days after application Rate Treatment ppmw 30 days 70 days

Diquat* 1. 0 30 80 Diquat 0. 5 100 9 0+ Diquat + CuSO4 O. 5 + O. 5 100 100 Diquat + CuSO4 0.25 + 0.25 80 90+ 90+ Diquat + Tryad O. 5 + 1 50 pt/gal Diquat + CuSO4 + 0. 5 + 0. 5 + 50 30+ Tryad 1 pt/gal

* Extremely turbid water + Regrowth occurred 168 Appendix Table 26.Evaluation of controlof E. densa bydiquat and diquat combinations InvestigatoryTrial2, 1969. % control ofE. densa Rate Treatment ppmw 14 days 28 days Diquat 1.0 30 95 Diquat O. 5 40 90 Diquat 0.25 40 90 CuSO4 0.5 10 10 Diquat + CuSO4 0. 5 + 0.5 30 80 Diquat + CuSO4 0.25 + 0.25 20 50 Diquat + CuSO4 0.1 + 0.25 0 45 Diquat + Endothall O. 5 + O. 5 20 100 Diquat + Endothall 0.25 + 0.5 10 65 Control 0 0

Appendix Table 27.Visual evaluation of controlof E. densa by diquat and diquat combinations,Investigatory Trial 3, 1969. % control of E. densa Rate Treatment ppmw 14 days 28 days Diquat 1.0 30 40 Diquat 0. 5 20 20 Diquat 0.25 10 10 Diquat 0.1 0 0 Diquat + CuSO4 0. 5 + 0.5 30 30 Diquat + CuSO4 0.25 + 0.5 20 20 Diquat + CuSO4 0.1 + 0.5 0 CuSO4 O. 5 0 0 Diquat + Endothall 0. 5 + 0. 5 0 30 Diquat + Endothall 0.25 + 0.25 0 20 Diquat + Endothall 0.1 + 0.1 0 0 Endothall 0. 5 0 0 Control 0 0 169

Appendix Table 29.Results of analysis for diquatcation in samples of E. densa for Field Trial 3.

Diquatcation ppmw Date Plot Rate after Corrected Check RecoveryFortified no. Treatment ppmw treatment absorbance Found corrected correctedrecovery (%)

26.90 1 Diquat 1.0 9 days 1.20 22.8 22.8

2 Diquat 0. 5 9 I, 1.15 21. 8 21.8 25.72

3 Diquat 0. 25 9 II 0.352 2. 88 2. 88 3. 40

4 Diquat + 0. 5 + 9 II 1. 26 23. 94 23.94 28.25 CuSO4 0. 5

5 Diquat + 0. 25 + 9 " 0.381 7. 24 7. 24 8. 54 CuSO4 0. 5

6 Diquat + 0. 5 + 9 II 0.481 9. 14 9. 14 10.78 Endothall 0. 5

7 Diquat + 0. 25 + 9 " 0. 255 4. 85 4. 85 5. 72 Endothall 0.25

25.11 1 Diquat 1.0 18 days 1.12 21. 28 21.28

2 Diquat 0.5 18 " 1.02 19.38 19.38 22.87

3 Diquat 0. 25 18 " 0. 420 7. 98 7. 98 9. 42

4 Diquat + 0. 5 + 18 " 0.324 6. 16 6. 16 7.27 CuSO4 0. 5

5 Diquat + 0. 25 + 18 " . 423 8.04 8.04 9. 49 CuSO4 0.5

6 Diquat + 0. 5 + 18 " . 502 9. 54 9.54 11.26 Endothall 0. 5 7 Diquat + 0.25 + 18 " 0.219 4. 16 4. 16 4.91 Endothall 0.25

Drift 18 " 0. 108 2.05 2. 05 2. 42 sample Fortified check Diquat 1.0 0.45 0.85 0.85 1.00 85 Check 0.000 0.000 StandardDiquat 1.0 . 130 170

Appendix Table 30.Water temperature and light attenuation in open and "weedy" water, Field Trial 3. oC Temperature Profile

Water depth (ft. ) Open Water "Weedy" Water

0 18.4 18.4 2 18.4 18.4 4 18.4 18.4 6 17.7 17.8 8 17.7 17.1 10 16.8 16.9

Light Attenuation

Reading on photometer (microamperes) Open water "Weedy" water' Water depth No Red Green Blue No Red Green Blue (meters) filter filter filter filter filter filter filter filter

0 2100 950 225 410 2100 950 225 410 0.25 - 15 0.5 9.5 1.5 0.5 - - - - 0.5 0.0 1.5 0.5 1.0 350 16 32 5.5 0.0 0.0 0.0 0.0 2.0 95 2 7 1.2 - - 3.0 5 0.5 0.5 0.4

1/100%infestation of E. densa 171 Appendix Table 31.Cost of shoreline treatments with diquat and dichlobenil.

Diquat 1 mile 8 feet wide = 1 acre 1 mile 50 feet wide = 6.25 acres Average depth of 50' strip = 10 feet Acre feet/mile - Booth Arm = 62.5 acre ft. 1,0 ppm in 1 acre foot requires 2.7 lb. active chemical 0.25 ppm in 1 acre foot requires 0.675 lb. active chemical 0.25 ppm62.5 acre foot requires 62.5 x 0.675 lb. active chemical = 42.2 lbs. Diquat required @ 2 lbs. per gallon for 1 mile at 0.25 ppm = 21 gallons Diquat at $20 per galloncost per mile = $410.

Dichlobenil 10 lbs active per acre = 62.5 lbs. mile 4% granule, 100 lbs granules = 4 lbs. 1560 lbs granules = 62.5 lbs 100 lbs granules @ $50 Cost dichlobenil at 10 lbs. active per mile is $730.