72-^694
WORTHINGTON, James Price, 1935- THE EFFECT OF ALACHLOR AND MON-097 ON THE GROWTH OF YELLOW NUTSEDGE AND THE UPTAKE OF 1**C LABELED ALACHLOR BY YELLOW NUTSEDGE ! AND SOYBEANS.
The Ohio State University, Ph.D., 1971 Agronomy
University Microfilms, A XERQ\Company, Ann Arbor, Michigan
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED THE EFFECT OF AIACIILOU AND HON-097 ON THE GROWTH OF YELLOW NUTSEDGE
AND THE UPTAKE OF 14C LABELED ALACHLOR BY YELLOW NUTSEDGE AND
SOYBEANS
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
By
James Price Worthington, B.S., M.S.
* * * * *
The Ohio State University 1971
Approved by
Adviser Department of Agronomy PLEASE NOTE:
Some Pages have indistinct print. Filmed as received.
UNIVERSITY MICROFILMS ACKNOWLEDGMENTS
Tho author wishes to express his appreciation to Dr. Edward
W. Stroube for his guidance and helpful advice throughout the years of study and in the preparation of the manuscript.
Appreciation is also expressed to Dr. Leo E. Bendixen and
Dr. Ralph Franklin for their assistance and helpful suggestions in conducting the investigations.
Appreciation is expressed to the Monsanto Company for the technical and labeled materials used in this study.
To my wife, Maxine, and our daughters, Kristal and Kelly, and son, Gregory, I am grateful for their patience, help and encouragement extended me during the years of this study.
ii VITA
January 6, 1935..Born— Conover, Ohio
1952-1953...... Ohio Wesleyan University, Delaware, Ohio
195 6 ...... B.S,,The Ohio State University, Columbus, Ohio
195 7 ...... M.S.,The Ohio State University, Columbus, Ohio
1958...... Sales Representative, Swift &Co., Greenville, Ohio
1958t1967...... Manager, Shepard Grain Co., Fletcher, Ohio
1967-196 8 ...... Manager, Little Elevator Co., Rockford, Ohio
1968-197 1 ...... Teaching Associate, The Ohio State University, Columbus, Ohio
FIELDS OF STUDY
MAJOR FIELD: Agronomy(V/eed Control)
Studies in Agronomy. Professors Bendixen, Franklin, Miller and Smith
Studies in Botany. Professors Blaydes, Meyer, Platt and Popham
Studies in Biochemistry. Professors Serif and Zubkoff
iii TABLE OF CONTENTS
Page ACKNOWLEDGMENTS ii
VITA iii-
LIST OF TABLES V
LIST OF FIGURES viii
INTRODUCTION 1
REVIEW OF LITERATURE 2
Yellow Nutsedge Reproductive Potential Tuber Germination Plant Development Control of Yellow Nutsedge Alachlor and MON-097 Herbicide Placement Herbicide Uptake by Soybeans
MATERIAL AND METHODS...... 9
Herbicide Rate Experiment Effect of Alachlor and M0N-097 Placement on Yellow Nutsedge Uptake of 14C Labeled Alachlor by Yellow Nutsedge Uptake of -*-4C Labeled Alachlor by Soybeans
RESULTS AND DISCUSSION...... 16
Herbicide Rate Experiment Dry Weight of Yellow Nutsedge Uptake of 14C Labeled Alachlor by Yellow Nutsedge Effect of Alachlor on Soybeans Uptake of 14C Labeled Alachlor by Soybeans
SUMMARY...... 57
LITERATURE CITED„...... 60
iv LIST OF TABLES
Table Page 1. Analysis and Properties of the Crosby Silt Loam used in all Experiments...... 9
2. Number of Emerged Plants Twelve Days after Planting when Alachlor and MGN-097 wore Incorporated into the Upper 2.5 cm of Soil...... 16
3. Analysis of Variance of the Alachlor Rate Test...... 17
4. Analysis of Variance of the MON-097 Rate Test...... 17
5. Number of Days to Emergence of Yellow Nutsedge Plants when Alachlor and M0N-097 were Incorporated into the Upper 2.5 cm of Soil at Various Rates...... 18
6. Analysis of Variance of the Number of Days to Emergence of Yellow Nutsedge Plants from Soil Treated with Various Rates of Alachlor...... 18
7. Analysis of Variance of the Number of Days to Emergence of Yellow Nutsedge Plants from Soil Treated with Various Rates of MON-097...... 19
8. Number of Shoots per Germinating Yellow Nutsedge Tuber from Soil Treated with Various Rates of Alachlor and MON-097...... 22
9. Analysis of Variance of the Number of Shoots per Germ inating Yellow Nutsedge Tuber from Soil Treated with Various Kates of Alachlor...... 22
10. Analysis of Variance of the Number of Shoots per Germ inating Yellow Nutsedge Tuber from Soil Treated with Various Rates of MON-097...... 23
11. Weight of Yellow Nutsedge Plants as Affected by Alachlor and M0N-097 Placement in Soil...... 27
12. Weight of Yellow Nutsedge Plant Sections in mg per Germ inating Tuber as Affected by Alachlor and MON-097 Placement in Soil...... 29
v Table Pane 13. Average Weight of Yellow Nutsedge Plant Sections in rag per Germinating Tuber...... 33
14. Analysis of Variance of Dry Weights of Yellow Nutsedge as Affected by Herbicides and Plant Section 34
15. Dry Weight of Yellow Nutsedge Shoots, Above Plus Below Ground, in mg per Germinating Tuber as Affected by Alachlor and MON-097 Placement in the Soil...... 35
16. Analysis of Variance of Dry Weights of Yellow Nutsedge Shoots, Above Plus Below Ground...... 35
17. Number of Yellow Nutsedge Shoots Emerged from the Soil and Developed from Tubers as Affected by Alachlor and MON-097 Placement in the Soil...... 37
18. Analysis of Variance of the Number of Emerging Yellow Nutsedge Shoots...... 38
19. Analysis of Variance of the Number of Shoots Developing from Yellow Nudsedge Tubers ...... 38
20. Radioactivity in Yellow Nutsedge Plants as Affected by Labeled Alachlor...... 41
21. Average Radioactivity in Yellow Nutsedge Plant Sections,. 42
22. Radioactivity in Yellow Nutsedge Shoots, Tubers, Tuber Rhizomes and Roots as Affected by Placement of 14c Labeled Alachlor in the Soil...... 43
23. Analysis of Variance of Radioactivity in Yellow Nutsedge Plants as Affected by 14c Labeled Alachlor Placement in the Soil and the Plant Section Analyzed,...... 43
24. Number of Yellow Nutsedge Shoots Emerged from the Soil and Number of Tuber Rhizomes Developed as Affected by Place ment of Alachlor in the Soil ...... 45
25. Analysis of Variance of the Number of Yellow Nutsedge Tuber Rhizomes Developed as Affected by Placement of Alachlor in the Soil ...... 46
26. Analysis of Variance of the Number of Yellow Nutsedge Shoots Emerged from the Soil as Affected by Alachlor Placement...... 46
27. Number of Emerging Soybeans as Affected by Alachlor Placement in the Soil ...... 47
vi Table Page 28. Analysis of Variance of the Number of Emerging Soybeans as Affected by Alachlor Placement in.the Soil...... 48
29. Fresh Weight of Soybean Shoots, Cotyledons, Hypocotyls, and Roots as Affected by Placement of Alachlor in the Soil...... 49
30. Fresh Weight of Soybean Plants as Affected by Placement of Alachlor in the Soil...... 49
31. Average Fresh Weights of Soybean Plant Sections...... 50
32. Analysis of Variance of Fresh Weights of Soybeans as Affected by Placement of Alachlor in the Soil...... 50
33. Average Radioactivity in Soybeans as Affected by Place ment of Alachlor in the Soil...... 52
34. Average Radioactivity in Soybean Plant Sections...... 53
35. Radioactivity in Soybean Shoots, Cotyledons, Hypocotyls, and Roots as Affected by Placement of Labeled Alachlor in Soil...... 54
36. Analysis of Variance of Radioactivity in Soybeans as Affected by Placement of 14c Labeled Alachlor in Soil.. 54
vii LI ST OF FIGURES
Figure Page 1. The Distribution of Yellow and Purple Nutsedge in the United States(32)...... 3
2. Drawing of Treatments in Experiments Involving Herbicide Placement. Yellow Nutsedge Tubers and Soybeans were Planted 3.8 cm Below in Soil Surface. Alachlor and MON-097 were Placed in the Upper 2.5 cm, 2.5-5.0 cm and 5.0-7.5 cm Soil Layers. The Soil Surface was Covered with 1.3 cm of Quartz Sand...... 12
3. Diagram of Yellow Nutsedge...... 15
4. Typical Growth of Yellow Nutsedge when Alachlor was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,1,2, and 3 ppm...... 20
5. Typical Growth of Yellow Nutsedge when Alachlor was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,3,6, and 12 ppm...... 20
6. Typical Growth of Yellow Nutsedge when M0N-097 was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,1,2, and 3 ppm...... 21
7. Typical Growth of Yellow Nutsedge when MON-097 was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,3,6, and 12 ppm...... 21
8. Typical Above Ground Growth of Yellow Nutsedge Plants Treated with Alachlor at the Rate of 2 ppm in the Upper 2.5 cm Layer (Above),' the 2.5-5.0 cm Layer (With), and the 5.0-7.5 cm Layer (Below)...... 24
9. Typical Above Ground Growth of Yellow Nutsedge Plants Treated with MON-097 at the Rate of 0.5 ppm in the Upper 2.5 cm Layer (Above), the 2.5-5.0 cm Layer (With) and the 5.0-7.5 cm Layer (Below)...... 24
10. Typical Below Ground Growth of Yellow Nutsedge Plants Treated with Alachlor at the Rate of 2 ppm in the Upper 2.5 cm Layer (Above), the 2.5-5.0 era Layer (With), and the 5.0-7.5 cm Layer (Below) ...... 26
vi:-1 Figure Page 11. Typical Below Ground Growth of Yellow Nutsedge Plants Treated with MON-097 at the Rate of 0.5 ppm in the Upper 2.5 cm Layer (Above), the 2.5-5.0 cm Layer (With), and the 5.0-7.5 cm Layer (Below)...... 26
12. Dry Weight of Yellow Nutsedge Plants when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Below the Soil Surface ...... 28
13. Dry Weight of Yellow Nutsedge Roots when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Below the Soil Surface...... 30
14. Dry Weight of Yellow Nutsedge Above Ground Shoots when Treated with Alachlor and M0N-097, Tubers were Planted 3.8 cm Below the Soil Surface...... 31
15. Dry Weight of Yellow Nutsedge Below Ground Shoots when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Below the Soil Surface...... 32
16. Dry Weight of Yellow Nutsedge Shoots, Above Plus Below Ground, when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Below the Soil Surface...... 36
17. Number of Yellow Nutsedge Shoots Emerged when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Below the Soil Surface...... 39
18. Number of Shoots Developed from Yellow Nutsedge Tubers when Treated with Alachlor and M0N-097. Tubers were Planted 3.8 cm Below the Soil Surface...... 40
19. Uptake of Radioactivity from Labeled Alachlor by Yellow Nutsedge Plants...... 44
20. Fresh Weights of Soybean Plants when Treated with Alachlor...... 51
21. Uptake of Radioactivity from Labeled Alachlor by Soybeans...... 55
ix INTRODUCTION
Yellow nutsedge, Cyperus esculentus L.,is a problem weed in much of the United States. In Ohio, it is an increasing problem in
the agronomic crops, especially corn and soybeans. Yellow nutsedge
is difficult to control because it reproduces sexually by seeds and
asexually by rhizomes which may terminate in new shoots or tubers.
The tubers are capable of producing several shoots.
Mechanical control of perennial weed species is extremely difficult, especially when the weed is capable of asexual reproduction.
Herbicides offer the greatest potential for control of these difficult to control weeds. Alachlor (2-chloro-2',6'-diethyl-N-(methoxy- metb'1 lacetanilide), has provided some control of yellow nutsedge in soybeans, Glycine max L., and corn, Zea mays L . , Alachlor was developed by Monsanto Company in 1967 and marketed as Lasso. M0N-097
(2-chloro-N~(ethoxy-methyl)-6’-ethyl-o-acetotoluidide), an experimental herbicide developed by Monsanto Company, has also appeared effective for yellow nutsedge control in corn and soybeans.
The objective of this study was to determine the effect of depth of placement of alachlor and MON-097 on the development of yellow nutsedge, the effect of depth of placement of alachlor on the development of soybeans and to determine the effect of depth of placement on the uptake of alachlor by yellow nutsedge and soybeans.
1 REVIEW OF LITERATURE
Yellow Nutsedge
Yellow nutsedge is a perennial herbaceous sedge which
reproduces by seeds, rhizomes, and tubers(32). The plant is native
to North American and is found in most of the United States(32)
(Figure 1). Yellow nutsedge is a problem of economic Importance in many states(2,32,33). It was an increasing problem in many states
and ranked fifth as a problem weed in the United States in 1965(33).
Yellow nutsedge is closely related to purple nutsedge,
Cyperus rotundus L., which was listed by Holm(lO) as the worst weed in the developing countries of the world. In the United States, purple nutsedge is found primarily in the southeast and the extreme southwest(32)(Figure 1). It is not a problem in Ohio. A major difference between yellow and purple nutsedge, is the location of tubers produced on the rhizomes. The tubers of yellow nutsedge are always in a terminal position on the rhizome but there may be several tubers produced in a chain on the rhizomes of purple nutsedge(2,12,34).
Reproductive Potential
Hill et al.(9) reported that during one growing season, a single seedling developed into a stand of plants which produced 90,000 seeds that germinated 51%. The average production was 36,500 seeds having an average of 46% germination. Ho observed that in dense, otS
^ Yellow Nutsedge
Purple Nutsedge
Figure 1.— The Distribution of Yellow and Purple Nutsedge in the United States(32).
to 4 undisturbed stands there was very little seed production. This work
"( indicates that seed production may be important only in the early establishment of yellow nutsedge.
The reproductive potential by tubers was investigated by
Tumbleson and Kommedahl(31). They found that plants developed from a single tuber produced nearly 6900 tubers the fall of the first season and 1900 plants the following spring. In peat soil infested with yellow nutsedge, an average of 8.3 tons per acre of tubers were harvested. Eighty-five per cent of these tubers were produced in the upper six inches of soil(2,31).
Tuber Germination
It was found that yellow nutsedge tubers may germinate from as deep as twelve inches in the soil and produce plants, but most germinated within the upper six inches of soil(l,2,31).
Yellow nutsedge tubers which were removed from the field during the winter or early spring germinated readily, but those removed during the late summer and early fall were apparently dormant
(1,2,29). In Delaware, few tubers survived and maintained viability more than two winters(2). Germination was increased in the field by mechanical disturbance(29) and in the laboratory by washing with water, chemical treatment or exposure to cold temperatures(1,2,28,30).
Washing apparently removed the compounds which inhibited germination of yellow nutsedge tubers. Tumbleson and Kommedahl(30) investigated the effect of dormant tuber extracts on germination. Germination of several grain and forage crop species as well as yel.low nutsedge was reduced or inhibited by these extracts. Yellow nutsedge tubers generally produced approximately one
shoot per tuber (2,8), although it was found that one tuber produced
as many as seven shoots.
Plant Development
It was found that the germinating tuber produced rhizomes
from the apical end(2,12). Each rhizome arising from a tuber,
differentiated into a crown, or basal bulb, below the soil surface.
Roots, horizontal rhizomes, and a shoot develop from this meristematic
area. The horizontal rhizomes terminated either as a shoot or a
tuber(2,3,12). Shoot formation, from horizontal rhizomes, was
promoted by high nitrogen levels, long photoperiods, high temp
eratures, and certain hormones(2,4,6,12). Tuber formation was
promoted by short photoperiods, high light intensity, high soil
temperatures and high soil fertility(2,6,12).
Jansen(12) reported that flowering occured at photoperiods
between twelve and fourteen hours.
Control of Yellow Nutsedge
The control of yellow nutsedge was primarily dependent on
the prevention of tuber production and germination. Keeley, Thullen
and Miller(15) indicated that the insect, Bactra veratana Zeller, was
specific for nutsedge and severely damaged the plant late in the
growing season. Early infestation by the insect was limited and many plants survived to produce tubers. Therefore, the insect was
limited as a biological control agent.
Mechanical control of yellow nutsedge has been difficult because of its vegetative reproduction. Tumbleson and Kommedahl(31)
reported that fallowing peat soil for four years greatly reduced,
but did not eliminate viable nutsedge tubers.
The difficulty of controlling yellow nutsedge by mechanical methods stimulated interest in chemical control methods. Several herbicides have been effective in reducing the stands of yellow nutsedge. DSMA(disodium methanearsonate) and MSMA(monosodium methane- arsonate) reduced the germination of tubers produced by treated
yellow nutsedge plants(14). Thiocarbamate herbicides were effective
in controlling growth of yellow nutsedge from tubers, especially when incorporated into the soil(2,7,11). Amitrole-T(3-amino-s-
triazole*ammonium thiocyanate), atrazine(2-chloro-4-(ethylamino)-
6-(isopropylamino)-s-triazine), and dalapon(2-2-dichloropropionic acid) have also been effective in reducing stands of yellow nutsedge(2).
Alachlor and MON-097
Alachlor(2-chloro-2*,6'-diethyl-N-(methoxymethyl)acetanilide),
and M0N-097(2-chloro-N-(ethoxymethyl)-6'-ethyl-o-acetotoluidide),
CH-* .Ct^-O-CH^CHg
C-GH,C1
closely related compounds, were effective in controlling yellow nutsedge(18,19). Alachlor was also effective for control of lambs- quarters, Chenopodium album L.,(21), giant foxtail,Setaria faberli
Herrin., (26), and several other grass and broadleaf weeds(18,25).
MON-097, an experimental herbicide, was effective for control of
several grass and broadleaf weeds(19). Alachlor was a selective
prcemergence herbicide for use in corn, soybeans and several other
crops(18).
Herbicide Placement
A number of studies have been initiated to determine where
the herbicide should be placed in relation to the germinating seed
(5,7,11,16,17,22,23). Thorough incorporation of preemergence herbicides have resulted in better weed control under all conditions
than partial incorporation(13). Most preemergence herbicides required at least some degree of incorporation.
Knalce and Wax(17) measured the effect of herbicides on giant foxtail shoots when the herbicide was placed in the root, seed, and shoot zones. They found alachlor was most effective when placed
in the shoot zone. Eshel(5) measured the effect of placement of
alachlor on cotton.Gossypium hirsutum L.,plants. He found that
alachlor was most toxic to cotton when the entire root system was
exposed to the herbicide. Reduction in seedling weight was accompanied
by severe inhibition of root growth. He concluded that selectivity
of alachlor was based on seeding depth protection and if the seeds wore not separated from the herbicide, the crop plants would be damaged.
Herbicide Uptake by Soybeans
Stoller and Wax(27) found that amiben(3-amino-2,5-dichloro- benzoic acid) was readily taken up by soybeans and several other plants but did not find any association between uptake and species sensitivity.
Moody, Kust and Buchholtz(20) found that the amount of root uptake of herbicides by soybeans was not a good indicator of toxicity. Uptake of herbicides by soybean seed was also measured. It was found that herbicides were absorbed by both viable and non-viable seeds(24), MATERIALS AND METHODS
The soil used in all experiments was a Crosby silt loam
taken from the Agronomy Farm at Columbus, Ohio. Detailed information on the soil is given in Table 1. Prior to use, the soil was steam sterilized at five pounds per square inch for fourteen hours to kill existing weed seed. Soil moisture was adjusted to twenty per cent by adding water with an atomizer to soil in a cement mixer, except as noted in the experiments. Water was not added during the experi ments .
TABLE 1.— Analysis and Properties of the Crosby Silt Loam used in all Experiments.
Determination Value
Per cent sand 24.9
Per cent silt 53.5
Per cent clay 21.6
Per cent organic matter 3.3
pH 6.7
Pounds of available phosphorusa 131
Pounds of available potassium13 301
Per cent moisture at 1/3 atmosphere 21.9
Pleasured by the Bray P^ method. Extracted with IN NH^OAc, measured by the atomic absorption method.
9 10
Tubers were harvested from a yellow nutsedge clone which was propagated in the greenhouse. The tubers were washed and stored at four degrees Centigrade at least three weeks prior to planting to break dormancy. These tubers were used in all experiments except the labeled alachlor study. Tubers for the labeled alachlor study were harvested in early April from a small area on the Agronomy Farm at
Columbus, Ohio. Uniform sized tubers were selected for planting.
The herbicides used were 92.7 per cent technical grade alachlor and 81.6 per cent technical grade MON-097 provided by the courtest of Monsanto Company, St. Louis, Missouri.
Alachlor is a cream colored solid at room temperature(18).
It is soluble in ether, acetone, benzene, and ethanol. The solubility of alachlor in water is 148 ppm. M0N-097 is a pale straw colored oil and has a solubility in water of 398 ppm(19).
Herbicide Rate Experiment
A herbicide rate experiment was conducted to determine an effective rate for use in subsequent experiments. Alachlor and M0N-097 were incorporated into the soil at 1,2,3,6, and 12 ppm. The soil to be treated was weighed and spread into a thin layer in a round pan.
Alachlor and MON-097 were applied in acetone solution with an atomizer to the soil surface. The acetone was allowed to evaporate before adding water to the soil. The soil moisture was increased to twenty per cent while the soil was continually mixed in a plastic container.
A 9 cm deep layer of moist soil was placed in each 15 cm plastic pot. Ten yellow nutsedge tubers were placed on the soil surface, covered with a 1.3 cm layer of untreated soil plus a 2.5 cm layer of treated soil. The tubers were soaked in water prior to planting to insure adequate moisture for early development. A layer, approximately 1.3 cm deep, of quartz sand was added to the soil surface to reduce evaporation losses.
Treatments were replicated three times in a randomized block design. Each herbicide comprised a separate experiment. The experiments were conducted in a growth chamber which was set for a twelve hour photoperiod, seventy-five degree Fahrenheit days and sixty-eight degree Fahrenheit nights. Light intensity was approx imately 3500 foot candles.
Observations of time of emergence, moisture stress, and number of emerged plants were recorded. The experiments were term inated after three weeks and the number of underground shoots was recorded.
Effect of Alachlor and MON-097 Placement on Yellow Nutsedge
Alachlor and M0N-097 were incorporated in layers as shown in Figure 2. The yellow nutsedge tubers were planted 3.8 cm below the soil surface. The soil surface was covered with a 1.3 cm layer of quartz sand to reduce surface moisture losses. The placement technique was modified from one described by Knalce and Wax(17).
Alachlor was incorporated into the soil at a rate of 2 ppm by weight and MON-097 was added at the rate of 0.5 ppm by weight.
The herbicides were applied to the soil in acetone solution with an atomizer while mixing in a cement mixer. After allowing the acetone to evaporate, water was added to bring the soil up to twenty per cent moisture. (wtffeffil Sand |------1 Tuber or Seed fflnjflflJAi m / i m Herbicide
,a^oPyo^o°oaoao0d^dP3 fe^ Check Upper 2.5 cm 2.5—5.0 cm 5.0-7.5 cm Figure 2.— Drawing of Treatments in Experiments Involving Herbicide Placement. Yellow Nutsedge Tubers and Soybeans were Planted 3.8 cm Below the Soil Surface. Alachlor and MON-097 were Placed in the Upper 2.5 cm, 2.5-5.0 cm and 5.0-7.5 cm Soil Layers. The Soil Surfacd was Covered with 1.3 cm of Quartz Sand. n 13 Ten presoaked yellow .nutsedge tubers were planted in each 15 cm plastic pot. Treatments were replicated five times in a randomized block design. The experiment was conducted in the growth chamber as previously described. Observations and the number of emerged plants were recorded. The experiment was terminated after sixteen days. The number of rhizomes and oven dry weights of above ground shoots, below ground shoots, and roots were recorded. Uptake of Labeled Alachlor by Yellow Nutsedge The water and labelled alachlor were added with a pipette to soil in a plastic bag and allowed to set sixteen hours. Mixing was accomplished by rolling and kneading the soil in the plastic bag. Alachlor treated soil was placed in layers above, with, or below the tubers as previously described, except in this experiment 10 cm pots were used. The smaller pots were used to keep the amount of contaminated soil at a minimum. Five tubers were planted 3.8 cm below the soil surface and the soil surface was covered with a 1.3 cm layer of quartz sand to reduce moisture losses. Alachlor was incorp orated into the soil at the rate of 2 ppm by weight on an oven dry soil basis. Seventy per cent of the alachlor was technical grade and thirty per cent was uniformly labeled with ^he benzene ring. The labeled alachlor had a specific activity of 1.02 millicuries per millimole. Treatments were replicated four times in a randomized block design. The pots were placed in the growth chamber set for a fourteen hour photoperiod, eighty degree Fahrenheit days and seventy-two degree 14 Fahrenheit nights. The number of yellow nutsedge plants emerging"from the soil was recorded and after thirteen days, plants were harvested. The plants were removed from the soil and washed in tap water to remove all soil. Excess water was blotted off and the plants were divided into four sections, the shoot, tuber, tuber rhizomes, and roots. The shoot was defined as the upper portion of the yellow nutsedge plant beginning at the base of the crown, or basal bulb. The "tuber rhizome" was defined as any rhizome arising from the tuber (Figure 3). Each plant section was homogenized with eighty per cent ethanol in a Virtis "23" research grinder. The extract was filtered through Whatman No. 1 filter paper and collected in a twenty ml vial. The volume was reduced by evaporation in an oven at fifty-five degrees Centigrade and adjusted to ten ml. Two ml aliquots were evaporated in plastic planchets. Radioactivity was measured with a thin window, gas flow counter. Uptake of labeled Alachlor by Soybeans The procedure for measurement of the uptake of labeled alachlor by soybeans was essentially the same as for yellow nutsedge. Five soybeans were planted in each 10 cm pot. Treatments were replicated five times in a randomized block design. The number of emerging plants was recorded. Plants were harvested ten days after planting. Radioactivity measurements were made on the shoot, coty ledons, hypocotyls, and roots. Fresh weights of each of these plant sections were also recorded. 15 Leaves Basal Soil Surface Bulb Primary Roots Rhizome Tuber Rhizome New Original Tuber Tuber Roots Figure 3.— Diagram of Yellow Nutsedge. RESULTS AND DISCUSSION Herbicide Rate Experiment The results of the herbicide rate experiment indicated that alachlor and MON-097 were effective in reducing the growth of yellow nutsedge, Alachlor applied at 1 ppm was not different from the check treatment. At the rate of 2 ppm, alachlor reduced the number of emerged plants by approximately fifty per cent. There was essentially no emergence of yellow nutsedge plants when alachlor was applied at rates of 3,6, and 12 ppm. MON-097 applied at rates of 1 ppm or more resulted in complete or nearly complete elimination of yellow nutsedge plant growth. The results and analysis of the number of emerging yellow nutsedge plants are shown in Tables 2,3, and 4. TABLE 2.— Number of Emerged Plants Twelve Days after Planting when Alachlor and MON-097 were Incorporated into the Upper 2.5 cm of Soil Rate Alachlor0, MON-097a (ppm) (plants/pot) (plants/pot) 0 11.00b 11.00b 1 10.67b 2.00a 2 5.67c 0.00a 3 1.00a 0.00a 6 0.00a 0.00a 12 0.00a 0.00a OMeans in a column followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of three replications. 16 17 TABLE 3.— Analysis of Variance of the Alachlor Rate Test. Source of variation df SS MS F Total 17 415.62 Replication 2 0.12 0.06 0.04 Treatments 5 402.28 80.45 60.94++ Error 10 13.22 1.32 ♦♦Significant at the 1% level. TABLE 4.— Analysis of Variance of the M0N-■097 Rate Test. Source of variation df SS MS F Total 17 304.50 Replication 2 2.33 1.17 1.00 Treatments 5 290.50 58.10 49.65++ Error 10 11.67 1.17 ♦♦Significant at the 1% level. On the basis of these results, rates were estimated that would give approximately fifty per cent control of yellow nutsedge plants. In subsequent experiments, alachlor was applied at the rate of 2 ppm and MON-097 was applied at the rate of 0.5 ppm. Alachlor applied at rates up to 2 ppm did not delay emerg ence ofyellow nutsedge plants. At rates of 3 and 6 ppm, emergence was progressively delayed and at the 12 ppm rate, there were no emerged plants when the experiment was terminated. Application of MON-097 at rates of 1 and 2 ppm delayed emergence of yellow nutsedge plants and at rates of 3,6, and 12 ppm there were no emerged yellow nutsedge plants when the experiment was terminated. The results and 18 analysis of the data on the number of days to emergence of yellow nutsedge as affected by alachlor and MON-097 are shown in Tables 5, 6, and 7. TABLE 5.— Number of Days to Emergence of Yellow Nutsedge Plants when Alachlor and M0N-097 were Incorporated into the Upper 2.5 cm of Soil at Various Rates. Rate Alachlora M0N-097a (ppm) (days) (days) 0 7.00a 6.00a 1 7.00a 12.66ab 2 7.33a 17.33b 3 13.33b 6 17.33c 12 * * » 4 • • • • • * aMeans in a column followed by the same letter are not significantly different at the 1% level as deteimined by Duncan’s multiple range test. Blank areas in the column indicate no emergence of plants when the experiment was terminated. Each value is the mean of three replications. TABLE 6.— Analysis of Variance of the Number of Days to Emergence of Yellow Nutsedge Plants from Soil Treated with Various Rates of Alachlor. Source of variation df SS MS F Total 14 273.60 Replications 2 0.40 0.20 0.03 Treatments 4 267.60 66.90 95.57** Error 8 5.60 0.70 **Signifleant at the 1% level. 19 TABLE 7.— Analysis of Variance of the Number of Days to Emergence of Yellow Nutsedge Plants from Soil Treated with Various Rates of MON-OD7. Source of variation df SS MS F Total 8 218.00 Replications 2 4.67 2.34 0.50 Treatments 2 194.66 97.33 20.84** Error 4 18.67 4.67 **Signi£icant at the 17® level. Although all differences were not significant, there was a trend for an increase in the number of tuber rhizomes developed with increases in the rate of application of alachlor and MON-097. When alachlor and M0N-097 were applied at rates of 3 and 1 ppm respectively, there were over two tuber rhizomes produced per tuber. This corresponds with the first significant rates at which yellow nutsedge emergence was delayed. Apparently, the first tuber rhizome absorbed a sufficient amount of the herbicide to be killed and the second tuber rhizome developed from the tuber, resulting in delayed emergence of the shoot. Tubers with short tuber rhizomes and emerged shoots are shown in Figures 4,5, and 6. The maximum number of tuber rhizomes produced was three when treated with alachlor and four when treated with MON-097. The results and analysis of the data on the number of tuber rhizomes p^r germinating tuber are shown in Tables 8,9, and 10, and Figures 4,5,6, and 7. In the alachlor experiment, there was branching of the shoots formed at the apical end of tuber rhizomes when treated at the 12 ppm rate. This occurred less frequent at the 6 ppm rate and occasionally Figure 4.— Typical Growth of Yellow Nutsedge when Alachlor was Incorporated into tho Upper 2.5 cm of Soil at Rates of 0,1,2, and 3 ppm. CHECK fiialhtoR PPm f l t A c h h * Alfibi/op £ p p m I t P P M Figure 5.— Typical Growth of Yellow Nutsedge when Alachlor was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,3,6, and 12 ppm. 21 m f - o i 7 £ H E C K I /PPM 'ARMPO? 7 /M09-0?7 - 2 PPA1 3 P P M Figure 6.— Typical Growth of Yellow Nutsedge when MON-097 was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,1,2, and 3 ppm. M / 7 - O T 7 6 PPM Figure 7.— Typical Growth of Yellow Nutsedge when MON-097 was Incorporated into the Upper 2.5 cm of Soil at Rates of 0,3,6, and 12 ppm. 22 at the 3 ppm rate. In the MON-097 experiment, branching was observed occasionally at the 2 ppm rate and not at other rates. Yellow nutsedge plants which emerged through the alachlor and M0N-097 treated layers appeared to grow as well as the check plants. TABLE 8.— Number of Shoots per Germinating Yellow Nutsedge Tuber from Soil Treated with Various Rates of Alachlor and M0N-097. Rate Alachlor3- MON-097a (ppm) (shoots/tuber) (shoots/tuber) 0 1.17a 1.10c 1 1.20a 2.20a 2 1.70c 2.60ab 3 2.30b 2.63ab 6 2.37b 2.73ab 12 2.73b 2.87b % e a n s in a column followed by the same letter are not significantly different at the 1 % level as determined by Duncan's multiple range test. Each value is the mean of three replications. TABLE 9,— Analysis of Variance of the Number of Shoots per Germinating Yellow Nutsedge Tuber from Soil Treated with Various Rates of Alachlor. Source of variation df SS MS F Total 17 6.72 Replications 2 0.02 0.010 0.36 Treatments 5 6.42 1.280 45.71** Error 10 0.28 0.028 **Significant at the X% level. 23 TABLE 10.— Analysis of Variance of the Number of Shoots per Germinating Yellow Nutsedge Tuber from Soil Treated with Various Rates of M0N-097, Source of variation df SS MS F Total 17 6.91 Replications 2 0,02 0.010 0.21 Treatments 5 6.43 1.286 27.95++ Error 10 0.46 0.046 ♦♦Significant at the 1% level. At the termination of the experiment, the soil layer which was treated with 12 ppm alachlor was removed from one of the pots, replaced with untreated soil and placed in the growth chamber. Shoots, which appeared to be normal, emerged within a few days. These observations indicated that alachlor must be in contact with the active growth area of the yellow nutsedge plant to be effective. Sufficient levels of the herbicide are apparently not accumulated within the plant to be effective once the external source is removed.. The first appearance of moisture stress became evident after sixteen days in the alachlor study and after seventeen days in the MON-097 study. These observations were used as guidelines for harvest planning in subsequent experiments. Dry Weight of Yellow Nutsedge Alachlor and MON-097 were effective in reducing the dry weight of yellow nutsedge plants. Typical above ground growth of yellow nutsedge plants treated with alachlor and MON-097 is shown in Figures 8 and 9. The plants which developed in pots treated with alachlor and MON-097 in the 5.0-7,5 cm layer appeared to develop Figure 8.— Typical Above Ground Growth of Yellow Nutsedge Plants Treated with Alachlor at the Rate of 2 ppm in the Upper 2.5 cm Layer (Above), the 2,5-5.0 cm Layer (With), and the 5.0-7,5 cm Layer (Below). /MON-097 M0/V-09 7 M0N-O17 CHECK Qtlaui Tilt*** With Tuitm At*** Figure 9.--Typical Above Ground Growth of Yellow Nutsedge Plants Treated with MON-097 at the Rate of 0.5 ppm in the Upper 2.5 cm Layer (Above), the 2.5-5.0 cm Layer (With) and the 5,0-7.5 cm Layer (Below). 25 normally, but wero slightly shorter than the check plants. There was essentially no above ground growth when alachlor was placed in the upper 2.5 cm or the 2.5-5.0 cm soil layers. In the herbicide rate experiment, alachlor applied at the rate of 2 ppm reduced the number of emerged plants by approximately fifty per cent. In this study, alachlor, incorporated into the upper 2.5 cm of soil, reduced the number of emerged shoots more than ninety per cent. There were differences in the method of incorporation of alachlor into the soil. These differences suggest that it might be important to investigate the effect of the method of incorporation of alachlor on the control of yellow nutsedge. The method of incorporation has been shown to be important with other herbicides(14). The plants which emerged through the MON-097 treated layers appeared to have slightly broader leaves and exhibited formative effects. The smaller plants were a lighter green color. The root and shoot growth of yellow nutsedge was very reduced when alachlor and MON-097 were placed in the 2.5-5.0 cm soil layer with the tubers. Root growth was confined primarily to the upper layers when alachlor and MGN-097 were placed in the 5.0-7.5 cm soil layer below the yellow nutsedge tubers. Typical below ground growth of yellow nutsedge plants treated with alachlor and MON-097 is shown in Figures 10 and 11. There was no apparent moisture stress during the course of this experiment, Alachlor and M0N-097 were effective in reducing the dry weight of yellow nutsedge plants regardless of their placement in the 2G CHECK ALACHLOR \ I-I..,! !J1 flLACHLOK tor# trim {*,j W a l h l o r Bl &*U* 7V*#** Figure 10.— Typical Below Ground Growth of Yellow Nutsedge Plants Treated with Alachlor at the Rate of 2 ppm in the Upper 2,5 cm Layer (Above), the 2.5-5.0 cm Layer (With), and the 5.0-7.5 cm Layer (Below). f M o N-017 CHECK Aimt 7Uttt ■ w m ULtm 7Utm Figure 11.— Typical Below Ground Growth of Yellow Nutsedge Plants Treated with MON-097 at the Rato of 0.5 ppm in the Upper 2.5 cm Layer (Above), the 2.5-5.0 cm Layer (With), and the 5.0-7.5 cm Layer (Below). 27 soil (Table 11 and Figure 12). Both herbicides were equally most effective in reducing dry weights when placed with the yellow nutsedge tubers in the 2.5-5.0 cm soil layer. They were equally least effective when placed below the tubers in the 5.0-7.5 cm soil layer. Alachlor applied at the rate of 2 ppm was more effective than MON-097 applied at the rate of 0.5 ppm when placed above the tubers in the upper 2.5 cm soil layer. TABLE 11.— Weight of Yellow Nutsedge Plants as Affected by Alachlor and MON-097 Placement in Soil. Treatment Weighta (mg/tuber) Check 38,16e Alachlor(2ppm) Upper 2.5 cm 16.37b 2.5-5.0 cm 8.22a 5.0-7.5 cm 30.77d MON-097(O.Sppm) Upper 2.5 cm 24.37c 2.5-5.0 cm 8.28a 5.0-7.5 cm 29.85d uMeans followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications over all plant sections. Alachlor was more effective than M0N-097 in reducing the dry weight of roots and above ground shoots when both herbicides were placed in the upper 2.5 cm soil layer. Both herbicides were equally effective in increasing the dry weight of the below ground shoots of yellow nutsedge when placed in the upper 2.5 cm soil layer(Table 12 and 28 120' — — — Alachlor (2 ppm) MON-097 (0.5 ppm) 100 - 80- xo Xo u «H o 60- ■p c Q> o p o dt 40i S. S. 20- 0-2.5 2.5-5.0 5.0-7.5 Herbicide Placement (cm) Figure 12.— Dry Weight of Yellow Nutsedge Plants when Treated with Alachlor and MON-097. Tubers were Planted 3,8 cm Below the Soil Surface. 29 Figures 13,14, and 15), TABLE 12,— Weight of Yellow Nutsedge Plant Sections in rag per Germ inating Tuber as Affected by Alachlor and MGN-097 Placement in Soil.a Treatment Above Ground Below Ground ltoots Shoots Shoots (mg/tuber) (mg/tuber) (mg/tuber) Check 5 5 ,62m 34.42h 2 4 .46g Alachlor(2 ppm) Upper 2,5 cm 0.24ab 36.88ijk 12.00d 2.5-5.0 cm 0.00a 21.12f 3.54c 5.0-7.5 cm 36.16i jk 37.76jk 18.38ef M0N-097(0.5 ppm) Upper 2.5 cm 18.22ef 39.141c 1 5 ,76e 2.5-5.0 cm 0.54abc 21.08f 3.22bc 5 .0-7.5 cm 35.40ij 37.12ijk 17.04e aMeans followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications, When placed in the 2.5-5.0 cm soil layer, alachlor and M0N- 097 were equally effective in reducing the dry weight of roots, above ground shoots, and below ground shoots of yellow nutsedge. When placed in the 5.0-7,5 cm soil layer, alachlor and M0N- 097 were equally effective in reducing the dry weights of roots and above ground shoots and in increasing the dry weights of below ground shoots. The reduction of the dry weight of above ground shoots may have been the result of root pruning(Figures 10 and 11). The increased dry weight of below ground shoots was apparently due to the increased number of below ground shoots. This increase also occurred when alachlor and M0N-097 were placed in the upper 2.5 cm soil layer. The 30 120, — Alachlor (2 ppm) — MON-097 (0.5 ppm) 100- 80- 60- 40- 20 0-2.5 2.5-5.0 5.0-7,5 Herbicide Placement (cm) Figure 13.— Dry Weight of Yellow Nutsedge Roots when Treated with Alachlor and MGN-097. Tubers were Planted 3.8 cm Below the Soil Surface, 31 120-, — Alachlor (2 ppm) — MON-097 (0.5 ppm) 100- 80- 60- 40- 20- 0-2.5 2.5-5.0 5.0-7.5 Herbicide Placement (cm) Figure 14.— Dry Weight of Yellow Nutsedge Above Ground Shoots when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Delow the Soil Surface. 32 120- 100 - 80- a u Alachlor (2.ppm) M0N-097 (0.5 ppm) 20 - 0 ■ .. ( -I,. i------1---- 0-2.5 2.5-5.0 5.0-7.5 Herbicide Placement (cm) Figure 15.— Dry Weight of Yellow Nutsedge Below Ground Shoots when Treated with Alachlor and MON-097. Tubers were Planted 3.8 cm Below the Soil Surface. inhibition of growth when alachlor and MON-097 were placed with the tubers in the 2,5-5.0 cm soil layer was apparently sufficient to reduce dry weights of the below ground shoots even though thero were increased numbers of shoots. The mean dry weights of yellow nutsedge roots, above ground shoots, and below ground shoots were significantly different from each other(Tables 13 and 14). These differences were modified by the treatments. When the soil was treated with alachlor and M0N-097 in the 5.0-7,5 cm layer, the dry weights of above ground shoots were not different. The dry weights of roots and above ground shoots were not different when MQN-097 was placed in the upper 2.5 cm or the 2.5-5.0 cm soil layers(Table 12). TABLE 13.--Average weight of Yellow Nutsedge Plant Sections in mg per Germinating Tuber.a Plant Section Weight ______(mg/tuber)______ Above Ground Shoots 20.88a Below Ground Shoots 32.50b Roots 13.48c aMeans followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications over all treatments. 34 TABLE 14.— Analysis of Variance of Dry Weights of Yellow Nutsedge as Affected by Herbicides and Plant Section. Source of variation df SS MS F Total 104 25494.37 Replications 4 170.36 42.59 3.08+ Treatments 6 12220.75 2036.79 147.67++ Main Plot Error 24 331.01 13.79 Plant Section 2 6432.92 3216.46 1076.13+* Treatment x Section 12 6171.92 514.32 172.07++ Sub Plot Error 56 167.38 2.98 ♦Significant at the 5% level. ♦♦Significant at the 1% level • All herbicide treatments reduced the total shoot weight of yellow nutsedge plants. Herbicide placement in the 2.5-5.0 cm soil layer was most effective in reducing shoot weights. Herbicide place- ment in the 5.0-7.5 cm soil layer was least effective in reducing the total shoot weight, Alachlor at the rate of 2 ppm was more effective than MON-097 at the rate of 0.5 ppm only when placed in the upper 2.5 cm soil layer. The results and analysis of the combined dry weights of the above and below ground shoots are shown in Tables 15 and 16 and in Figure 16. 35 TABLE 15.— Dry Weight of Yellow Nutsedge Shoots, Above Plus Below Ground, in mg per Germinating Tuber as Affected by Alachlor and MGN-097 Placement in the Soil.a Treatment Total Shoot Weight (mg/tuber) Check 90.04e Alachlor(2ppm) Upper 2.5 cm 37.12b 2.5-5.0 cm 21.12a 5.0-7.5 cm 73.92d M0N-097(O.Sppm) Upper 2.5 cm 57.36c 2.5-5.0 cm 21.62a 5.0-7.5 cm 72.52d aMeans followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications. TABLE 16,— Analysis of Variance of Dry Weights of Yellow Nutsedge Shoots, Above Plus Below Ground. Source of variation df SS MS F Total 34 23171.37 Replications 4 292.63 73.15 3.08+ Treatments 6 22309.06 3718.17 156.64++ Error 24 569.67 23.73 ♦Significant at the 5% level. ♦♦Significant at the 17o level. There were no differences in the number of shoots emerged from the soil when not treated or when treated with alachlor and M0N-097 below the tubers in the 5.0-7,5 cm soil layer. Alachlor and Below Ground, when Treated with Alachlor and MON-097, Tubers were Tubers and MON-097, with Alachlor Treated when Ground,Below Planted 3.8 cm Below theSurface.Soil cm Below 3.8 Planted Per Cent of Check Figure 16.— Dry Weight of Yellow Nutsedge Shoots, Above Plus Above Shoots,Nutsedge Yellow of Weight Dry 16.— Figure 100- 120-1 40- 20 60- 80- - 0-2.5 O-9 (. ppm) (0.5 MON-097 Aaho (2ppm) Alachlor — ebcd lcmn (cm) Placement Herbicide 2.5-5.0 5.0-7.5 MON-097 placed in the upper 2.5 cm or the 2.5-5.0 cm soil layers reduced the number of emerged yellow nutsedge shoots, MON-097 was more effective when placed in the 2.5-5.0 cm soil layer than when placed in the upper 2.5 cm or the 5.0-7.5 cm soil layers. Alachlor at the rate of 2 ppm was more effective than M0N-097 at the rate of 0.5 ppm when placed in either the upper 2,5 cm or the 2.5-5.0 era soil layers. The results and analysis of the number of emerged shoots and the number of shoots developed from yellow nutsedge tubers are given in Tables 17,18, and 19 and shown in Figures 17 and 18, TABLE 17,— Number of Yellow Nutsedge Shoots Emerged from the Soil and Developed from Tubers as Affected by Alachlor and MON-097 Placement in the Soil,a Treatment Emerged Shoots Shoots Developed (shoots/tuber) (shoots/tuber) Check 1 ,50d 1.64a Alachlor(2ppm) Upper 2.5 cm O.lOab 2.86c 2.5-5.0 era 0.00a 2.38b 5.0-7,5 cm 1.54d 1.64a MON-097(0.5ppm) Upper 2.5 cm 0,86c 2.48b 2.5-5.0 cm 0.28b 2.46b 5.0-7,5 cm 1,56d 1.64a aMeans in a column followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications. 38 TABLE 18.— Analysis of Variance of the Number of Emerging Yellow Nutsedge Shoots. Source of variation df SS MS F Total 34 15.6787 Replications 4 0.1531 0.0382 1.94 Treatments 6 15.0548 2.5091 128.01** Error 24 0.4707 0.0196 ♦♦Significant at the 17a level. TABLE 19.— Analysis of Variance of the Number of Shoots Developing from Yellow Nutsedge Tubers, Source of variation df SS MSF Total 34 8.3656 Replications 4 0.1514 0.0378 1.80 Treatments 6 7.7096 1.2849 61.18** Error 24 0.5045 0.0210 **Significant at the 1% level. There were no differences in the number of shoots developed per germinating tuber when not treated or when treated with alachlor or M0N-097 below the yellow nutsedge tubers in the 5.0-7.5 cm soil layers. The greatest number of shoots per germinating tuber resulted when alachlor was placed in the upper 2.5 cm soil layer. Treatments which reduced the number of emerged shoots increased the number of shoots developing from the yellow nutsedge tubers. These data indicate that MON-097 applied to the soil at the 39 120-t Alachlor (2 ppm) MON-097 (0.5 ppm) 100- 80- it o o J3 O o 60- ■p c O CJ M (!) ft 40- 20 - / 0 0-2.5 2.5-5.0 5.0-7.5 Herbicide Placement (cm) Figure 17.— Number of Yellow Nutsedge Shoots Emerged when Treated with Alachlor and MON-097. Tubers were Planted 3,8 cm Below the Soil Surface. '10 200- 180- 160- o 140- 4J C O o u 0J 0« 120- 100- — Alachlor (2 ppm) MON-097 (0.5 ppm) X 0-2.5 2.5-5.0 5.0-7.5 Herbicide Placement (cm) Figure 18.— Number of Shoots Developed from Yellow Nutsedge Tubers when Treated with Alachlor and M0N-097. Tubers were Planted 3.8 cm Below the Soil Surface, 41 rate of 0.5 ppm was equally effective as alachlor applied at the rate of 2 ppm when placed with or below yellow nutsedge tubers. When applied above the tubers, alachlor was more effective than MON-097 in reducing the growth of yellow nutsedge plants. In the herbicide rate experiment, MON-097 applied at the 1 ppm rate appeared to be more effective than alachlor applied at the 2 ppm rate in reducing the emergence of yellow nutsedge plants. Therefore, it appeared that MON-097 was between two and four times more active per unit than alachlor on the growth of yellow nutsedge. Uptake of Labeled Alachlor by Yellow Nutsedge A significant amount of radioactivity was counted in all alachlor treated plants (Table 20). The number of counts per minute in yellow nutsedge check plants was assumed to be the result of background radioactivity. There was no difference in the amount of radioactivity between plants grown in soil treated with labeled alachlor in the upper 2,5 cm soil layer and in the 5.0-7.5 cm soil layer. TABLE 20.— Radioactivity in Yellow Nutsedge Plants as Affected by *-4C Labeled Alachlor.a Treatment Radioactivity (cpm/plant) Check 2.56a Upper 2.5 cm 9.18b 2.5-5.0 cm 20.81c 5,0-7,5 cm 11.75b “Means followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of four replications over all plant sections. 42 There were no differences in the average amount of radio activity in yellow nutsedge shoots, tubers, tuber rhizomes, and roots (Table 21). TABLE 21.— Average Radioactivity in Yellow Nutsedge Plant Sections.a Plant Section Radioactivity (cpm/plant) Shoots 10.50a Tubers 12.18a Tuber Rhizomes 12.31a Roots 9.31a aMeans followed by the same letter are not significantly different at the 17o level as determined by Duncan's multiple range test. Each value is the mean of four replications averaged over all treatments. There was a significant amount of radioactivity counted in yellow nutsedge tubers and tuber rhizomes when labeled alachlor was placed with the tubers in the 2.5-5.0 cm soil layer (Tables 22 and 23 and Figure 19). Application of labeled alachlor in the 2.5-5.0 cm soil layer with the tubers, resulted in the largest amount of radioactivity in yellow nutsedge plants. This appeared to be the result of the large amount of absorption by yellow nutsedge- tubers. There was a significant amount of radioactivity in the roots of yellow nutsedge when labeled alachlor was placed below the tubers in the 5.0-7.5 cm soil layer. There was an increased amount of radioactivity in the shoots when labeled alachlor was applied above or below the tubers. There was no shoot development when the labeled alachlor was placed with the tuber, in the 2.5-5.0 cm soil layer, therefore those values wore background counts. 43 TABLE 22.— Radioactivity in Yellow Nutsedge Shoots, Tubers, Tuber Rhizomes and Roots as Affected by Placement of Labeled Alachlor in the Soil.a ______Plant Section______Treatment Shoots Tubers Tuber Rhizomes Roots ______(cpm/plant) ______ Checlc 3.25a 2.25a 2.50a 2.25a Upper 2.5 cm 20.25c 2.50a ll.OOab 3.00a 2.5-5.0 cm 3.00a 40.50e 31,75d 8.00ab 5.0-7.5 cm 15.50bc 3.50a 4.00a 24.OOcd “Means followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of four replications. TABLE 23.— Analysis of Variance of Radioactivity in Yellow Nutsedge Plants as Affected by Labeled Alachlor Placement in the Soil and the Plant Section Analyzed. Source of variation df SS MS F Total 63 9794.60 Replications 3 170.42 56.80 2.49 Treatments 3 2740.79 913.59 40.17** Main Plot Error 9 204.64 22.73 Plant Section 3 99.29 33.09 1.66 Treatment x Section 9 5861.75 651.30 34.11** Sub Plot Error 36 717.69 19.93 ♦♦Significant at the 1 % level. 44 — Tubers -Tuber Rhizomes Roots •-Shoots 30- -p a ctf H eu u 0) a 0) +» a 20- a •H a p 0> a U) p a a o o 10- 0-2.52.5-5.0 5.0-7.5 Herbicide Placement (cm) Figure 19.— Uptake of Radioactivity from Labeled Alachlor by Yellow Nutsedge Plants. 45 The radioactivity found in the sections of the yellow nutsedge plants appears to be closely associated with placement of labeled alachlor in the soil except for the amount found in shoots. There appeared to be movement of radioactive compounds from the roots to the shoot when labeled alachlor was applied below the tubers in the 5.0-7.5 cm soil layer. Therb was no other evidence of movement of radioactive compounds. The identity of the radioactive compound or compounds in the yellow nutsedge plants was not determined. The results and analysis of the effect of 14C labeled alachlor on the number of shoots and tuber rhizomes developed from yellow nutsedge tubers is shown in Tables 24,25, and 26. There were no emerged shoots when alachlor was placed in the upper 2.5 cm or the 2.5-5.0 cm soil layers. There was no difference between the numbers of shoots produced in the check pot and when alachlor was placed below the tubers in the 5.0-7.5 cm soil layer. These data essentially agree with those in the previous experiment. TABUE 24.— Number of Yellow Nutsedge Shoots Emerged from the Soil and Number of Tuber Rhizomes Developed as Affected by Placement of Alachlor in the Soil.® Treatment Tuber Rhizomes Emerged Shoots (per tuber) (per tuber) Check 1.55a 1.40b Upper 2.5 cm 1.75a 0.00a 2.5-5.0 cm 2.45b 0.00a 5.0-7.5 cm 1.30a 1.00b aMeans in a column followed by the same letter are ’->ot significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of four replications. 46 TABLE 25.— Analysis of Variance of the Number of Yellow Nutsedge Tuber Rhizomes Developed as Affected by Placement of Alachlor in the Soil. Source of variation df SS MS F Total 15 7.70 Replications 3 2.85 0.950 4.46^ Treatments 3 2.93 0.977 4.58+ Error 9 1.92 0.213 ♦Significant at the 5% level. TABUS 26,— Analysis of Variance of the Number of Yellow Nutsedge Shoots Emerged from the Soil as Affected by Alachlor Placement. Source of variation df SS MSF Total 15 6.80 Replications 3 0.26 0.086 1.69 Treatments 3 6.08 2.026 39.65^ Error 9 0.46 0.051 ♦♦Significant at the 1% level * There were more tuber rhizomes produced when alachlor was placed in the 2.5-5.0 cm soil layer with the tubers. No other differences were significant. The average number of tuber rhizomes produced when alachlor was placed in the upper 2.5 cm soil layer was only slightly greater than the number of tuber rhizomes in the check treatment. This difference was significant in two previous experiments. The amount of uptake of alachlor from the soil by yellow nutsedge plants was not a good indicator of the control of growth. 47 For example, there was very little difference in the amount of radio activity in yellow nutsedge plants treated in the upper 2.5 cm and in the 5.0-7.5 cm soil layers, but there was a highly significant difference in the dry weights of yellow nutsedge plants. The control of yellow nutsedge appeared to be dependent on the placement of alachlor in the soil. Alachlor appeared to control growth of the portion of the yellow nutsedge plant which it contacted directly. Elimination of above ground growth of yellow nutsedge required placement of alachlor in the upper layers of soil either with or above the tubers. It may be that alachlor was rapidly metabolized once it entered the plant, and the translocated compound measured in the shoot when labeled alachlor was placed below the tubers was an inactive metabolite. Effect of Alachlor on Soybeans There were no significant differences between treatments in the emergence of soybeans. The results and analysis of soybean emergence are shown in Tables 27 and 28. TABLE 27.--Number of Emerging Soybeans as Affected by Alachlor Place ment in the Soil.a Treatment______Plants per Pot Check 4.80 Upper 2.5 cm 5.00 2.5-5.0 cm * 00 o 5.0-7.5 cm 4.80 uEach value is the mean of five replications. There were no significant differences, 48 TABLE 28.— Analysis of Variance of the Number of Emerging Soybeans as Affected by Alachlor Placement in the Soil. Source of variation df SS MS F Total 19 2.55 Replications 4 0.30 0.075 0.42 Treatments 3 0.15 0.050 0.28 Error 12 2.10 0.175 Soybeans appeared to be resistant to alachlor, regardless of soil placement. There were no significant differences duo to treat ments in the average fresh weights of soybean plants. There were no significant differences due to treatments in the fresh weights of soybean shoots, cotyledons, or hypocotyls. The fresh weight of soybean roots was less when alachlor was placed in the upper 2.5 cm soil layer than when placed in the 5.0-7.5 cm soil layer. The difference in root weights appeared to have little value because these weights were not significantly different from the root weights in the check treatment. The results and analysis of the effect of alachlor pi .cement in the soil on the fresh weights of soybeans are shown in Tables 29,30,31, and 32 and in Figure 20. 49 TABLE 29.— Fresh Weight of Soybean Shoots, Cotyledons, Hypocotyls, and Roots as Affected by Placement of Alachlor in the Soil.a Plant Section Treatment Shoots Cotyledons Hypocotyls Roots (mg/plant) (mg/plant) (mg/plant) (mg/plant) Check 119.44a 257.04cde 165.56b 259.88cde Upper 2.5 cm 110.76a 234.40c 162.96b 239.96cd 2.5-5.0 cm 118.96a 259.OOcde 166.52b 261,44de 5,0-7,5 cm 109.80a 256.52cde 159.32b 279.40c the 5% level as determined by Duncan's multiple range test. Each value is the mean of five replications. TABLE 30.— Fresh Weight of Soybean Plants as Affected by Placement of Alachlor in the Soil.a Treatment Weight ______(mg/plant)______ Check 200.48a Upper 2.5 cm 187.02a 2.5-5.0 cm 201.48a 5.0-7.5 cm______201.26a______aMcans followed by the same letter are not significantly different at the 5% level as determined by Duncan's multiple range test. Each value is the mean of five replications averaged over all plant sections. 50 TABLE 31.— Average Fresh Weights of Soybean Plant Sections.a Plant Section Weight (mg/plant) Shoots 114.74a Cotyledons 251.74c Hypocotyls 163.59b Hoots 260.17c aMeans followed by the same letter are not significantly different at the 5% level as determined by Duncan's multiple range test. Each value is the mean of five replications averaged over all treatments. TABLE 32.— Analysis of Variance of Fresh Weights of Soybeans as Affected by Placement of Alachlor in the Soil. Source of variation df SS MS F Total 79 330358.62 Replications 4 717.89 179.47 0.21 Treatments 3 2973.45 991.15 1.16 Main Plot Error 12 10270.39 855.86 >> Plant Section 3 297370.62 99123.50 306.52** Section x Treatment 9 3503.93 389.32 1.20 Sub Plot Error 48 15522.19 323.37 ♦♦Significant at the 1% level. 51 270* 250 230 Roots Cotyledons Hypocotyls 210 Shoots p a ri bfl 190 e p J3 bfl •iH ISO* 130 110- — ^ ------1 — Check 0-2.5 2.5-5.0 5.0-7.5 Herbicide Placement Figure 20.— Fresh Weights of Soybean Plants when Treated with Alachlor. Uptake of Labeled Alachlor by Soybeans The greatest number of counts per minute per soybean plant was found when labeled alachlor was placed below the seeds in the 5.0-7.5 cm soil layer (Table 33).. Placement of labeled alachlor in the 2.5-5.0 cm soil layer resulted in a smaller, but significant, amount of radioactivity. There was no significant difference between the amount of radioactivity counted in soybean plants which were not treated and those which were treated with labeled alachlor in the upper 2.5 cm soil layer. The number of counts per minute in check plants was considered to be background radioactivity. TABLE 33.— Average Radioactivity in Soybeans as Affected by Placement of Alachlor in the Soil.a Treatment Radioactivity ______(cpm/plant) Check 3.63a Upper 2.5 cm 7.19a 2.5—5,0 cm 45.08b 5.0-7.5 cm 87.09c “Means followed by the same letter arc not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications averaged over all plant sections. The largest amount of radioactivity, when averaged over all treatments, was found in soybean roots. The smallest amounts were found in soybean shoots and hypocotyls(Table 34). 53 TABLE 34,— Average Radioactivity in Soybean Plant Sections,® Plant Section Radioactivity (cpm/plant) Shoots 17.33a Cotyledons 26.70b Hypocotyls 16.62a Roots 82.33c aMeans followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications averaged over all treatments. The amount of radioactivity found in the shoots, cotyledons, hypocotyls, and roots of soybeans appeared to be closely related to the placement of labeled alachlor in the soil. When labeled alachlor was placed in the upper 2.5 cm soil layer there were no significant differences between the amount of radioactivity in shoots, cotyledons, hypocotyls, and roots. Apparently, the cotyledons and hypocotyls emerged through the treated layer rapidly enough to minimize the uptake of alachlor. When labeled alachlor was placed in •** the 2.5-5.0 cm soil layer with the soybean seed, significant amounts of radioactivity were found in the cotyledons, hypocotyls, and roots. When labeled alachlor was placed below the soybean seeds in the 5.0- 7.5 cm soil layer, the largest amount of radioactivity was found in the roots(Tables 35 and 36 and Figure 21). It appeared that most of the radioactivity was due to absorption of -^C labeled alachlor, with possibly a portion due to upward translocation. 54 TABLE 35.— Radioactivity in Soybean Shoots, Cotyledons, Hypocotyls, and Roots as Affected by Placement of 14c Labeled Alachlor in Soil.11 Plant Section Treatment Shoots Cotyledons Hypocotyls Roots (cpm/plant) (cpm/plant) (cpm/plant) (cpm/plant) Check 3.66a 3.66a 3.58a 3.62a Upper 2.5 cm 4.66a 7.88a 12.50a 3.72a 2.5-5.0 cm 17.48a 55.28c 33.34b 74.24d 5.0-7.5 cm 43.54bc 40.00b 17,06a 247.760 aMeans followed by the same letter are not significantly different at the 1% level as determined by Duncan's multiple range test. Each value is the mean of five replications. TABLE 36.— Analysis of Variance of Radioactivity in Soybeans as Affected by Placement of Labeled Alachlor in Soil. Source of variation df SS MS F Total 79 280330.68 Replications 4 1082.29 270.57 2.85 Treatments 3 91405.87 30468.G2 321.54** Main Plot Error 12 1137.09 94.75 Plant Section 3 59140.63 19713.54 311.74** Section x Treatment 9 124529.37 13836.59 218.80** Error 48 3035.31 63.23 **Significant at the l7o level • The greatest amount of radioactivity in soybeans shoots occurred when labeled alachlor was placed in the 5.0-7.5 cm soil Jiyer. This indicates that upward translocation of labeled compounds occurred in soybeans plants. The identity of the labeled compound or 55 Roots 240 — Cotyledons Hypocotyls Shoots 210- 180- ■p C3 cd 150- H a \ s a o >1 120- p > •H •P U cd o t! 90 •o od 60- 30- 0-2.5 2.5-5.0 5 .0-7.5 Herbicide Placement (cm) Figure 21.— Uptake of Radioactivity from Labeled Alachlor by Soybeans, compound:; was not determined. It also appeared that movement into the cotyledons and hypocotyls occurred when labeled alachlor was placed in the 5.0-7,5 cm soil layer. There was no indication of downward movement of radioactive compounds in soybean plants. The basis for selectivity of alachlor on yellow nutsedge and soybeans does not appear to be the result of differences in uptake of the herbicide by the plants. These results agree with previous experiments with soybeans and other plant species (20,27). Selectivity may be due to differences in metabolism or it may be that alachlor does not have the configuration necessary to inhibit growth reactions in soybeans. Both plants absorb measurable quantities of alachlor, but only yellow nutsedge growth is inhibited. SUMMARY Growth chamber studies were conducted to determine the effect of rate of application of alachlor and M0N-097 on the growth of yellow nutsedge plants, the effect of soil placement of alachlor and MON-097 on the growth of yellow nutsedge plants, the effect of soil placement of labeled alachlor on uptake by yellow nutsedge and soybean plants, and the effect of soil placement of alachlor on the growth of soybean plants. The results of these investigations are summarized as follows: 1. Alachlor applied at the rate of 1 ppm did not inhibit growth of yellow nutsedge plants. Fifty per cent inhibition was obtained when alachlor was applied at the rate of 2 ppm and rates of 3 ppm or greater gave complete or nearly complete inhibition of growth. 2. MON-097 inhibited growth of yellow nutsedge plants at rates of 1 ppm or higher. 3. Shoots emerging through alachlor treated layers appeared to develop normally. Shoots emerging through MON-097 treated layers had slightly broader leaves and exhibited formative effects. 4. Alachlor and M0N-097 progressively delayed the emergence of yellow nutsedge plants and increased the number of tuber rhizomes developed from each tuber as rates were increased. 5. Alachlor and MON-097 were most effective in reducing the above ground growth of yellow nutsedge plants and increasing the 57 58 number of underground shoots when placed in either the upper 2.5 cm or the 2,5-5.0 cm soil layers. They were not effective in reducing the number of shoots when placed in the 5.0-7,5 cm soil layer, 6. Alachlor and MON-097 were effective in retarding growth of yellow nutsedge shoots and roots. 7. Alachlor at the 2 ppm rate was slightly more effective in reducing the dry weight of yellow nutsedge plants than MON-097 at the 0.5 ppm rate. 8. Yellow nutsedge tubers accumulated radioactivity only when placed in direct contact with labeled alachlor. 9. The radioactivity in tuber rhizomes and roots of yellow nutsedge was higher when labeled alachlor was placed in their area of growth. 10. There appeared to be upward movement of radioactivity into the shoots when labeled alachlor was placed below the tubers in the 5.0-7,5 cm soil layer. 11. The uptake of radioactivity from alachlor was not a good indicator of control of yellow nutsedge. 12. Alachlor had no effect on emergence or fresh weight of soybean plants, 13. The radioactivity in the cotyledons, hypocotyls, and roots was greatest when labeled alachlor was placed in their area of growth. 14. The upward movement of radioactivity was apparently the cause of the accumulation in soybean shoots when labeled alachlor was placed below the seed in the 5.0-7.5 cm soil layer. 15. Significant amouiits of radioactivity from labeled alachlor was measured in yellow nutsedge and soybean plants. 16. The basis for selectivity does not appear to be the result of differences in uptake of the herbicide by the plants, but may be due to differences in metabolism of alachlor. LITERATURE CITED 1. Andersen, Robert N. 1968. Germination and Establishment of Weeds for Experimental Purposes. W.F. Humphrey Press, Inc. Geneva, N.Y. 236pp. 2. Bell, R.S., W.H. Lachman, E.M, Rahn and R.D. Sweet, 1962. Life History Studies as Related to Weed Control in the Northeast-1. Northern Nutgrass. Rhode Island Agr. Exp. Sta. Bui. 364. 33pp. 3. Bendixen, Leo E. 1970. Validity of Evaluating Transformation of Primary Rhizomes in Yellow Nutsedge. Weed Sci. 18:408-409. 4. Bendixen, Leo E. 1970, Altering Growth Form to Precondition Yellow Nutsedge for Control. Weed Sci. 18:599-603. 5. Eshol, Y. 1969. Phytotoxicity, Leachability, and Site of Uptake of 2~chloro-21,6'-diethyl-N-(methoxymethyl)acetanilide. Weed Sci. 17:441-444. 6. Garg, D.K., L.E. Bendixen and S.R. Anderson. 1967. 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