WEED CONTROL Research Report

,, \ . ,,.--.... University 1of California . WEED CONTROL Research Report

WOODY PLANT CONTROL IN CALIFORNIA WIL.DLANDS

1973

1 Division of Agricu~ltural Sciences

Co•OperOtlve htension work in Agriculture and Home Economics, College of Agric.u11u_re, Univeriily of California, ond United Stoles OepartmE!nt of Agriculture co-operating. Distributed in furtherance of the Acts of Congrea of May 8, and June ~p., ]9J.4. George B. Alcorn, Director, California Agricultural Extension Service.

{NOT FOR PUBLl·CATION} MA-77 UNIVERSITY OF CALIFORNIA Woocly Plant Control in California Wildlands 1973

This report contains results of woody plant control experiments conducted throughout California.

Contributing Authors:

w. Brooks w. Mason c. Elmore w. McHenry R. Glenn R. Mullen w. Hamilton s. Radosevich w. Harvey A. Scarlett w. Johnson N. Smith o. Leonard w. Spivey

Compiled by:

Steven R. Radosevich, Extension Weed Scientist, University of California, Davts, California

The results presented in this report are part of ongoing research projects and should not in any way be interpreted as recommendations of the University of C~lifornia.

The University of California's Cooperative Extension programs ore a"voiloble to all, without regard to race, color, or notional origin. i

TABLE OF CONTENTS

Page Herbicide List 1

Weed Species Present in Herbicide Tests 2 1. Control of snowbrush ceanothus and greenleaf 4 manzanita in a stand of young conifers 2. Control of brush in a young stand of white fir 6 3. Comparison of six herbicides for the control of 6 California scrub oak 4. Control of mature brush with soil and foliar 10 applied herbicides 5. Applications of tebuthiuron for control of four 12 woody species 6. Effect ot dicamba in combination with 2,4-D and 12 2,4,5-T on the control of sprouting manzanita and interior live oak 7. Kill of poison oak with glyphosate 13 8. Control of sprouting eucalyptus stumps 14 9. Frill application of glyphosate and 2,4-D ester 15 for the control of California black oak 10. Response of squarrose knapweed (Centaurea squarrosa) 15 on rangeland to picloram and 2,4-D 11. Himalaya blackberry response to five foliage applied 16 herbicides 12. Bracken fern control using several foliage applied 17 herbicides 13. Residues of 2,4-D, 2,4,5-T, and silvex in range 18 forage Summary of several years studies for brush control 23 1. Chamise 23 2. Interior live oak 23 3. Canyon live oak and tan oak 24 4. Mountain misery (bear-mat) 24 5. Ponderosa pine and incense cedar selectivity 25 6. Poison oak · 25 1. In , HERBICIDE LIST

Herbicides Appearing in This Report

Common or Manufacturer or Code Name Trade Name Marketin~ Agency amitrole various various ammonium sulf'amate various various "\ asulam Asulox® Rhodia Inc. , Chipman Div borax various various broax + monuron Ureabor® u. s. Borax bromacil Hyvar-x® duPont

2,4-D various various 2,4-DP various various 0 dicamba Banvel® Velsicol f'enuron Dybar® duPont glyphosate Roundup© Monsanto karbutilate Tandex® Niagara picloram Tordon® Dow ,, silvex various various

2,4,5-T various various ' tebuthiuron Spike® Elanco

,,r'\ ' I 2. ~. WEED SPECIES PRESENT IN HERBICIDE TESTS I

Coim!lon Name Latin Name blue gum Eucalyptus globulus bracken fern pteridium aquilinum broadleaf filaree Erodium botrys bur clover Medicago hispida California black oak Quercus kelloggii California scrub oak Quercus dumosa caeyon live oak Quercus chrysolepis chamise Adenostoma fasciculatum chinquapin Castanea sp. clover Trifolium microcephalum clover Trifolium microdon clover Trifolium gracilentum coast fiddleneck Amsinckia intermedia fescue Festuca dertonensis foxtail barley Hordeum jubatum greenleaf manzanita Arctostaphylo~ patula Himalaya blackberry Rubus procerus hoary manzani ta Arctostaphylos canescens incense cedar Libocedrus decurrens interior live oak Quercus wislizeni lupine Lupinus sp. mountain misery Chamaebatia foliolosa pine Pinus sp. I 3. Common Name Latin Name poison oak mi.us toxicodendron ponderosa pine Pinus ponderosa rattail fescue Festuca myuros redstem filaree Erodium cicutarium ripgut brome Bromus rigidus slender oat Avena barbata snowbrush ceanothus Ceanothus velutinus soft chess Bromus mollis sprouting manzanita Arctostaphylos glandulosa squarrose knapweed Centaurea squarrosa tan oak Lithocarpus densiflora white fir Abies concolor wild barley Hordeum leporinum willow Salix sp. 4.

Control of snowbrush ceanothus and greenleaf manzanita in a stand of young conifers. Radosevich, s. R. and A. L. Scarlett. Undesirable brush species can severely reduce growth of young coniferous trees attempting to re-establish on many clear-cut or burned-over areas of California's potential timberland. A study was initiated on September 28, 1972 near Sattley, Sierra County to compare the effectiveness of 2,4-D ester, 2,4,5-T, and glyphosate for the control of greenleaf manzanita (Arctostap los patula Greene.) and snowbrush ceanothus (Ceanothus velutinus Dougl. growing in a stand of young ponderosa pine and white fir. Treatments were applied in / 3.7 GPA using a backpack mistblower. Plot size was 880 ft2 and 3 replications were employed. Diesel oil was used at l gal/A in the 2,4-D and 2,4,5-T treatments. At the time of application foliage was wet from rainfall the previous two days. Manzanita was 4 to 5 feet tall with numerous fir and pine growing above and below the tops of the brush. Care was taken to avoid direct spraying of conifers protruding above the brush.

Response of manzanita was acceptable with either rate of 2,~-D and 4 lbs. of 2,4,5-T. However both exhibited some phytotoxicity to white fir. Control of snowbrush ceanothus was marginal one year after application. Glyphosate was somewhat the opposite, giving acceptable control of ceanothus at the 4 and 8 lb. level, but only slight response was noted on manzanita after one year. Injury to white fir was substantially less with glyphosate than with either phenoxy herbicide. Limited data on injury to pines was due to lack of stand uniformity. It is important to note that at the time of application only 20 trees were above the brushline in the experimental area and trees in the understory were observed with difficulty. One year after treatment 40 trees existed above the brushline and an additional 110 trees could be easily seen. Trees present in the control plots were observed with difficulty.

While this trial is continuing to evaluate the full effectiveness of each herbicide treatment these initial results indicate that significant competition release of conifers from brush may be possible by applications of 2,4-D ester, 2,4,5-T, or glyphosate. ,/ ) ) J

Table 1. Response of greenleaf manzanita, snowbrush ceanothus am two coniferous tree species to three foliage applied- - herbicide ::, . Rate Control 0 = none. 10 = complete Injury 0 = none. 10 = dead Herbicide lb/A (ai) greenleaf manzanita ceanothus white fir pine o/5/73 10/2/73 6/5/73 10/2/73 6/5/73 10/2/73 6/5/73 10/2/73 2,4-D ester+ oil 2 5.7 7.3 5.7 2 2 2.3 1 0 2,4-D ester+ oil 4 7.0 8.3 8.3 5 2 5 o.8 0 2,4,5-T ester+ oil 2 8.o 5.3 9.3 4.3 o.8 1.3 1 - 2,4,5-T ester+ oil 4 8.3 8.3 9.6 7 2.2 3.8 - - glyphosate 2 3.7 1.7 7.0 2 0.3 0.2 - - glyphosate 4 6.3 2.3 6.5 7.3 0.7 0.5 0 - glyphosate 8 6.5 3 9.5 7.8 1 0.7 - - control - 0 0 0 0 0 0 0 0

Table 2. Number of coniferous trees above and below the brush treated with three foliage active herbicides

' I ,_, White fir Pine Herbicide Rate (lb/A) Above brushline Below brushline Above brushline- - Below brushline 2,4-D (ester) 2 1 15 3 4 2,4-D (ester) 4 3 12 2 2 2,4,5-T 2 1 8 0 l 2,4,5-T 4 0 16 2 l glyphosate 2 3 20 1 l glyphosate 4 11 11 2 2 glyphosate 8 3 7 2 0 control - 6 15 0 0 Total 28 104 12 11

\J1 • 6.

Control of brush in a young stand of white fir. Radosevich, s. R. and A. L. Scarlett. On September 28, 1972 near Sattley, Sierra County, California, a trial was established to determine the effectiveness of 2,4-D for the control of ceanothus and greenleaf manzanita growing on a site believed to contain a population of white fir. Eight replications were employed using a plot size of 2200 ft 2 • Applications were made from a crawler tractor which carried a portable engine driven piston sprayer connected to a single off-center nozzle. Spray volume was 80 GPA using a pressure of 40 psi. The only treatment consisted of 4 lb (ae)/A 2,4-D plus 1 GPA diesel oil. Rain had fallen for two consecutive days before treatment, however foliage was dry at application.

Weed species present included greenleaf manzanita (Arctostaphvlos patulj), snowbrush ceanothus (Ceanothus velutinus), and some chinquapin (Castanea sp •• / All species were approximately 4-5 ft. tall. White fir consisted of varying sizes up to 6 ft. Tall fir standing above the brushline were not sprayed. Response of white fir and two brush species to 2,4-D b-5-73 10-2-73 Herbicide Rate/Acre Formulation manzanita white fir manzanita ceanothus white fir

2,4-D 4 lb 4 lb ae/gal 3.3 0.9 8.3 2.4 2.2 + diesel + 1 gal control - - 0 0 0 0 0 .0

O = no control or injury, 10 = complete control Control of greenleaf manzanita was acceptable, however ceanothus appeared to be more resistant to 2,4-D. Results on the limited stand of chinquapin were somewhat erratic with little control noted.

Since it is difficult to evaluate the effectiveness of control of any brush species in one year this trial will be under continued evaluation for several years.

Comparison of six herbicides for the control of California scrub oak. Radosevich, s. R. and R. J. Mullen. An experiment was initiated in the fall of 1972 to comµire the response of scrub oak (Quercus dumosa) to two soil-active and four foliage applied herbicides. The site selected was on the Courta Madera Ranch near Pine Valley, San Diego County, California. This area had been burned in a wildfire two years before and consisted of regrowth of existing plants as well as new seedlings. ~ randomized block design with four replications was used. Plot size was 440 ft (.001 acre). The soil consisted of 3-3% O.M., 14% clay, 24% silt, and 62% sand. 7.

Fall treatments were applied December 18, 1972 and consisted of tebuthiuron applied as a wettable powder, granular and bolus formulation; bromacil as a wettable powder or granule; and glyphosate as a foliage spray. The bolus formulation of tebuthiuron was placed in rows with each bolus 5 ft. apart. This was intended to reduce the effect on the desirable grass and forbs while still giving control of scrub oak.

Additional treatments made on May 9, 1973 consisted of 2,4-D ester, 2,4,5-T, and silvex applied with either 1 GPA of diesel or isoparraffinic oil; a combination of 2,4-D and 2,4,5-T plus 1 GPA diesel; and glyphosate. All spray applications were made using a CO~ sprayer with a volume of 37 GPA. Granular and bolus formulations were appli~d by hand.

Results: Tebuthiuron appears to be superior to bromacil for the control of scrub oak. There appears to be little difference in response between formulations of either tebuthiuron or bromacil. Fall applications of glyphosate were superior to spring treatments. All fall treatments severely reduced or completely killed the existing stand of grass and forbs.

Only slight differences were noted between spring applications of 2,4-D, 2,4,5-T, silvex, and a combination of 2,4-D and 2,4,5-T. There may be a slight 0 advantage of isoparraffifinic oil over diesel. Spring treatments will be evaluated once again in 1974 and retreated if required. Table 1. Control of brush from fall applications of several herbicides. Applied 12/18/72. Control O = none, 10 = complete Herbicide Rate/Acre Formulation 5-19-73 11-8-73 Scrub oak Chamise Grass & forbs s. oak> 1 1 s. oak< 1 ' Grass tebuthiuron 3 8oa/oWP 5.0 6.3 10.0 7.3 6.3 10.0 tebuthiuron 12 8or/oWP 7.0 8.4 10.0 8.o 9.6 10.0 tebuthiuron 3 loa/o G 3.5 6.o 7.0 5.3 7.5 7-3 tebuthiuron l2 101, G 8.o 9.1 9.8 9.3 9.8 9. 3 tebuthiuron 6 bolus 4.5 6.o 6.o 6.o 5.5 6.3 tebuthiuron 12 bolus 5.9 6.7 10.0 8. 5 8.o 8.8 bromacil 3 80

CP •

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Table 2. Control of brush from spring applications of' several herbicides. Applied 5/9/73.

Control 0 = none, 10 = complete Herbicide Rate/Acre Formulation II-8-'(3 S. oaR:,=I I S. oalr<::'.I I C:rass

2,4-D + diesel 1 4 lb ae/gal 2.0 4.o 1.3 2,4-D + diesel 4 4 lb ae/gal 4.5 8.3 0

2,4,5-T + diesel 1 4 lb ae/gal 3.3 7.5 0 2,4,5-T + diesel 4 4 lb ae/gal 5.8 8.o 1.3 silvex + diesel 1 4 lb ae/gal 4.7 4.7 1.3 silvex + diesel 4 4 lb ae/gal 5.0 8.3 1.3

2,4-D + 2,4,5-T + diesel 1 + 1 4 lb ae/gal 5.3 6.5 0 2,4-D + 2,4,5-T + diesel 2 + 2 4 lb ae/gal 4.3 8.3 1.3

2,4-D + iso oil 1 4 lb ae/gal 3.5 6.o 2.5 2,4-D + iso oil 4 4 lb ae/gal 2.5 7.5 2.5

2,4,5-T + iso oil 1 4 lb ae/gal 6.o 7.3 3.3 2,4,5-T + iso oil 4 4 lb ae/gal 4.3 9.3 0 silvex + iso oil 1 4 lb ae/gal 4.5 6.8 0 silvex + iso oil 4 4 lb ae/gal 6-3 7.5 0 glyphosate L5 3 lb ae/gal 1.8 1.5 1.3 glyphosate 3 3 lb ae/gal 4.7 7.1 1.0 control - - 1-3 1.5 0 control - - 0 0 0

\0 • 10. ~,

Control of mature brush with soil and foliar applied herbicides. Radosevich, s. R. and R. J. Mullen. A San Diego County site on the Barona Indian Reservation heavily infested with chamise (Adenostoma fasciculatum) was selected to evaluate the effects of two soil-active and four foliage applied herbicides. Soil-active materials consisted of tebuthiuron and bromacil applied as a wettable powder and granular formulation. In addition tebuthiuron was tested as bolus (large pellets), applied in rows with each being 5 feet apart (i.e. l bolus/25 f't2 ). Granular formulations were applied by hand, a co2 sprayer used for the wettable powders. Bromacil and tebuthiuron applications were made December 20, 1972. Glyphosate, a foliage active material, was also applied at this time. Rainfall for the season following application totaled approximately 15 inches. On May 10, 1973 applications of 2,4-D ester, 2,4,5-T, and silvex plus one gallon per acre of either diesel oil or isoparaffinic oil; 2,4-D + 2,4,5-T plus 1 &PA diesel, and·glyphosate were made. 2 Four replications were employed with a plot size of 440 f't (. 001 acre), using a spray volume of 50 GPA~ The soil consisted of 0.15% O.M., 12% clay, 26% silt, and 62% sand. Chamise control bl several winter-applied herbicides {application date 12[20/72} Control O = nonez 10 = complete Herbicide Rate/Acre Formulation -5/8/73 11/9/73 Chamise Small forbs Chamise Grass & grasses

tebuthiuron 3 80

Chamise control of several herbicides applied in the spring application date 5/10 73 11 9 73 Herbicide Rate/Acre Formulation Chamise Grass

2,4-D + diesel 1 4 lb ae/gal 1.5 0 2,4-D + diesel 4 3.0 4-3 2,4,5-T + diesel 1 4 lb ae/gal 2.5 0 2,4,5~T + diesel 4 5.0 1.3 silvex + diesel 1 4 lb ae/gal 1.3 0 silvex + diesel 4 2.5 0 2,4-D + 2,4,5-T + diesel l + 1 4 lb ae/gal 3-3 2.5 2,4-D + 2,4,5-T + diesel 2 + 2 4.5 2.7 2,4-D + iso oil 1 4 lb ae/gal 4.5 1.8 2,4-D + iso oil 4 5.5 1.3 2,4,5-T + iso oil 1 4 lb ae/gal 4.o 1.3 2,4,5-T + iso oil 4 4.5 1.3 silvex + iso oil 1 4 .lb ae/gal 2.0 0 silvex + iso oil 1+ 4.7 3.7 glyphosate l, ~ 3 lb ae/gal 8.8 3.0 glyphosate ·~,,, 9.0 5.0 control 0 1.3 control 0.5 0

In comparing the two soil-active herbicides tebuthiuron exhibited greater control of charnise than did bromacil. Wettable powder formulations were slightly better than granules. Tebuthiuron bolus applications were designed to reduce the amount of toxicity to grass and forbs while still giving control of chamise. This did not prove to be the case as control of chamise was reduced greatly while toxicity to grass was only slightly lessened. Glyphosate applied in December gave excellent control of chamise at the 12 lb. level, however it also gave excellent control of grass and forbs.

Phenoxy herbicides applied in May and evaluated in November gave only moderate control. Another evaluation should be made in 1974 to more accurately measure their potential. Isoparraffinic oil appears to be giving better control than diesel when used with 2,4-D. Spring applications of glyphosate are showing excellent results with control at 1 1/2 lb/A about equal to 12 lb/A at this time. 12.

Applications of tebuthiuron for control of four woody species. McHenry, w. B., s. R. Radosevich, and w. Johnson. Tebuthiuron was applied as large pellet applications to four woody plant species to determine control and grass phytotoxicity. Study sites were selected for willow ( Salix sp. ) control (Yolo County), manzanita (Arctostap los sp.), black oak (Quercus velutina) and Himalaya blackberry Rubus procerus) control (Shasta County). Tbe herbicide was applied at rates of 6 and 12 lb/A (one pellet per 25 ft)2 in the fall or early spring. Species studied and dates of application are presented in the table below.

Species County Application date

willow Yolo 2/7/73 manzanita Shasta 10/25/73 black oak Shasta 10/25/73 Himalaya blackberry Shasta 10/25/73

Shasta County experiments received approximately 40 inches of rainfall after application, but the trial established in Yolo County received only 12-15 inches of precipitation.

The Shasta County experiments were.visually evaluated on July 11, 1973 while the trial in Yolo County was assessed on October 23, 1973. At these times of evaluation no effects were observed to any of the woody species. However severe grass removal was evident where the herbicide had been applied or where surface water had caused the chemical to move to previously untreated areas.

Effect of dicamba in combination with 2,4-D and 2,4,5-T on the control of sprouting manzanita and interior live oak. Leonard, o. A. and R. K. Glenn. Interior live oak (Quercus wislizenii var. fructescens) and sprouting manzanita (Arctostaphylos glandulosa) and hoary manzanita (Arctostaphylos canescens) were burned about 1966 along the firebreak of the James 1 pasture on the Hopland Experimental Range. Plots were established on June 29- 30, 1971 to determine if dicamba would enhance the herbicidal effectiveness of 2,4-D and 2,4,5-T against the above species. The dicamba alone and in combination with 2,4-D and 2,4,5-T were oil soluble formulations of Velsicol; since comparable formulations of 2,4-D and 2,4,5-T were not supplied by Velsicol, the PGBE (polyethylene glycol butyl ether) ester forms were used to estimate the effectiveness of these compounds without dicamba. Some plots were resprayed with the same materials on July 25, 1972. 13.

The data in the table below·indicate that dicamba did not enhance the effectiveness of either 2,4-D or 2,4,5-T against the species studied. Manzanitas were partly killed with one application and completely killed by two applications. A single application killed no interior live oak, but the second application 30 to 50% of the plants; previous experience would indicate that a third application would increase the kill to well above 90%. The kill achieved with 4 and 8 lbs. of 2,4-D or 2,4,5-T on live oak appeared to be essentially the same.

Kill of sprouting manzanita and interior live oak by one and two applications of 2,4-D and 2,4,5-T, with and without dicamba. The first spray was June 29-30, 1971 and the second spray was on July 25, 1972. Plant kill in percent Herbicid1e Treatment Rate[Acre manzanita interior live oak 1972 1973 1972 1973 none 0 0 0 dicamba.Y 4 0 0 dicamba 8 0 0 dicamba + 2,4-D 1 + 4 20 100 0 35 dicamba + 2,4-D 2 + 8 50 100 0 35 dicamba + 2,4,5-T 2 + 4 30 100 0 30 dicamba + 2,4,5-T 4 + 8 30 100 0 30 2,4-D 4 20 100 0 45 2,4-D 8 50 100 0 45 2,4,5-T 4 30 100 0 45 2,4,5-T 8 30 100 0 50

y •dicamba alone was not.applied again in 1972.

Kill of poison oak with gl phosate. Leonard, o. A., w. E. Mason ands. R. Radosevich. Poison oak Rhus toxicodendron) on the Wildberger ranch east of Lincoln, California was sprayed with 0.125, 0.25, 0.5, and 1.0% glyphosate in water on May 12, 1972. The bushes were uniformly sprayed but the foliage was not wet to runoff. Rates per acre are estimated to be o.6, 1.1, 2.2, and 4.4 lb/A. The best kill of poison oak was obtained with 1.0% glyphosate; the plant kill appeared to be 80 to 90%. Control with 0.5% glyphosate was about 30%, with many of the ~nkilled plants sprouting at the base. Lower dosages appeared to be relatively ineffective. The addition of the wetting agent, Superspread®, did not increase the effectiveness against poison oak. On the basis of these results, more trials with glyphosate for poison oak control should be made. I 14. Control of sprouting eucalyptus stumps. Radosevich, s. R., w. B. McHenry, w. D. Hamilton, and N. L. Smith. An experiment was initiated April 4, 1972 to determine a method of preventing resprouting of cut-over blue gum (Eucalyptus globulus Labill.). The trees had been cut, because _of winter-kill of the tops, about one month prior to initiating the study. Stump height varied from 30 to 90 cm, the diameter from 2-60 cm. Water soluble herbicides applied to frills cut immediately above the soil line were applied in full formulated strength or diluted 50% with water. Oil soluble herbicides were applied in diesel oil in a 20 to 30 cm band to the basal circumference of the stumps in sufficient volume to flow to and moisten the soi:J_.

A treatment unit consisted of ten stumps; three replications were employed. Percent control was determined by counting the stumps with no live sprouts compared to the number with one or more sprouts.

Eucalyptus stump sprout control

Herbicide Formulation Concentration o sprout control ai 7 19 73 Frill treatments

2,4-D dimethylamine 4 lb ae/gal 100% 100 2,4-D dimethylamine 4 lb ae/gal 50 97 2,4,5-T trimethylamine 4 lb ae/gal 100 93 2,4,5-T trimethylamine 4 lb ae/gal 50 92 ammonium sulfamate 95°/o w.s. 5 lb/gal 89 glyphosate 3 lb ae/gal 100% 92 glyphosate 3 lb ae/gal 50 100

Basal oil treatments 2,4-D isooctyl ester 4 lb ae/gal 16 lb 67 2,4,5-T butoxyethanol ester 4 lb ae/gal 16 lb 93 2,4-D butoxyethanol ester 2 lb+ 2 lb ae/gal 16 lb 87 + dichlorprop but. eth. ester silvex prop. glycol. but. 4 lb ae/gal 16 lb 77 ether ester control 0

All axe-frill treatments appear to be giving acceptable control at this time. Dilution of 2,4-D, 2,4,5-T, and glyphosate with 50% water did not reduce effectiveness. With the exception of 2,4,5-T ester, basal spray treatments were not as satisfactory. 15• .0 Frill application of glyphosate and 2,4-D ester for the control of California black oak. Scarlett, A. L., c. L. Elmore, s. R. Radosevich and R. K. Glenn. On July 7, 1972 a Plumas County site near Portola was selected to study the efficacy of glyphosate and 2,4-D ester for the control of California black oak (Quercus kelloggii). Frill cuts four inches apart into the xylem, each approximately 6 inches long were made with a hand axe, and herbicide applied in these cuts with a syringe. Cuts were made 16-32 in. above ground level into trees of varying diameter. Four replications were employed and each plot contained groups of one to six trees. Treatments consisted of glyphosate applied at 1 and 2 cc and 2,4-D ester at 2 cc per cut and a untreated control (frills only).

,, i Control of California black oak Rate/cut Control O = none, 10 = complete Herbicide cc 9/8/72 10/2/73 glyphosate 1 3.3 7.5 glyphosate 2 4.8 7.5 2,4-D 2 1.3 0.25 control 0 0

Acceptable results were obtained with glyphosate at both rates treated. The ester form of 2,4-D exhibited poor control; it is customary to use the amine formulation in this type of treatment which undoubtedly would have given better results.

Response of squarrose knapweed (Centaurea squarrosa Roth) on rangeland to picloram and 2,4-D. McHenry, w. B., w. R. Spivey and N. t. Smith. A study was initiated in 1973 to compare 2,4-D dimethylamine salt, 2,4-D isooctyl ester, and picloram for the control of squarrose knapweed on Lassen County rangeland. Spray volume was 80 gpa, plot size 200 sq. ft. with three replications. Knapweed pQpulation consisted of established plants 6-12 in. tall and immature rosettes 3-5 in. in diameter. Materials were applied with a knapsack sprayer fitted with a 3 nozzle boom. S uarrose kna eed control with 2 4-D amine Herbicide Formulation Acre rate A.I.

2,4-D amine 4 lb ae/gal 1 3.0 2,4-D amine 2 6.7 2,4-D amine 4 9.9 2,4-D ester 4 lb ae/gal l 4.7 2,4-D ester 2 9.7 2,4-D ester 4 9.9 picloram 2 lb ae/gal 0.5 9.8 picloram 1 10.0 ~\ control 0 16.

Picloram gave excellent control at rates tested. The ester formulation of 2,4-D was more effective than the amine at 1 and 2 lb ae/A. Treatments would have to be continued annually for eradication due to new seedling emergence.

Himalaya blackberry response to five foliage applied herbicides. McHenry, w. B. and w. Johnson. A Shasta County site near Whitmore was selected to study the effect of timing and spray volume on the response of blackberry (Rubus procerus) to 2,4-D LVE + 2,4,5-T LVE, silvex LVE and glyphosate. Two spray volumes were used. An engine driven high pressure sprayer was used to apply 120 GPA and a mist blower was used to apply the 6 GPA treatments. Diesel oil at 1~ of spray volume was ~dded to all high volume treatments. Plot sizes were either 900 or 1800 ft depending on the width of the blackberry stand. Fall application on September 19, 1972 will be compared to a spring treatment applied April 17, 1973. Both were retreated July 11; 1973. Control of Himala blackber Application rate Control 7 11 73 Herbicide lb/100 gal. lb/Acre Fall Spring High Volume Application

2,4-D + 2,4,5-T 1 + 1 1.2 + 1.2 2,4,5-T 2 2.4 silvex 2 2.4 silvex 4 4.8 Low Volume Application

silvex 5 0.3 2.0 2.5 silvex 10 o.6 2.0 1.0 silvex 20 1.2 4.o 2.0 glyphosate 5 0.3 0 2.0 glyphosate 10 o.6 3.0 2.0 glyphosate 20 1.2 5.0 5.5

At this time it appears that fall application is superior when high spray volumes are used. Low volume application exhibited no timing differences. Mist blower applications of glyphosate were slightly better than silvex at equal rates. 17.

Bracken fern control usi several folia e applied herbicides. Brooks, w. H. Bracken fern pteridium aquilinum can be a serious weed problem in dryland pastures. For this reason an experiment was initiated in Mendocino County to study the effects of several herbicides on this weed. All herbicides used in the trial were applied in 50 GPA of water with a backpack sprayer. A randomized block design with three replications was used. Herbicides used, rates applied and results obtained are presented below.

Bracken fern control with several foliage applied herbicides

V Bracken fern control Herbicide Rate (lb/A) 10/22/72 572773 '6/22/73 dicamba 2 2.3 1.0 1.0 dicamba 4 5.7 4.7 6.o dicamba 6 9.0 5.7 9.3 glyphosate 2 4.7 7.0 7.7 glyphosate 4 9.3 6.3 6.5 glyphosate 6 7.0 8.o 6.6 asulam 2 1.7 9.0 9.9 asulam 4 2.7 9.7 10.0 asulam 6 2.3 9.3 9.8 0 Visual evaluations for bracken fern control were made on August 22, 1972, May 2, 1973 and June 22, 1973. Glyphosate provided best control at the earliest date of evaluation. However, control one year after application had not significantly improved from the earlier rating. Asulam, one year after treatment was providing acceptable bracken fern control at all rates. 18.

Residues of 2,4-D, 2,4,5-T, and silvex in range forage. Harvey, w. A. and o. A. Leonard. Residues of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2(2,4,5-trichlorophenoxy) propionic acid (silvex) were determined af'ter their application to annual range vegetation. The herbicides were applied either in April, when the plants were growing rapidly, or in June when the plants were desiccated. The rate of loss was greater when application was to the dry forage, but the loss varied little among the different.herbicides. More than 98% of the herbicides originally present in the vegetation had disappeared by September 7 regardless of date of application. The herbicides were applied as the butoxyethanol esters, but only the acid forms were found in the samples.

Although livestock graze on phenoxy herbicide-treated pastures with apparent relish, or without apparent harmful effects, residues in such forage have been of concern. However, only limited information is available on the persistence of such herbicides in forage.

Klingman et al. studied the disappearance of 2,4-D from pastures sprayed with the butyland2-ethylhexyl esters. These studies were done in the eastern part of the United states, where growing conditions are good during the summer due to ample rainfall. Klingman et al. found that 92% of the 2,4-D had disappeared from the forage in 7 days when the butyl ester had been used; none of the residue was ester. However, when the 2-ethylhexyl·ester was used, 69% of the 2,4-D had disappeared; and about 10% of the 2,4-D was still in the ester form. The losses of 2,4-D took place in the absence of rain.

Recently, Morton et al. reported on the persistence of 2,4-D, 2,4,5-T, and dicamba in range forage grasses. They found that the herbicides disappeared at about the same rate. Rainfall was the most important factor influencing this.loss. They also found that the esters were lost rapidly, with only the acid forms of these herbicides being present af'ter one week.

Published information on the persistence of silvex in forage seems to be lacking. The purpose of the present study was to obtain data on the persistence of 2,4-D, 2,4,5-T, and silvex in the annual range forage of California. Since fairly high dosages of these herbicides must be used to control woody species, the residues remaining af'ter such applications were studied. I Plots 28 by 30 feet in size, replicated three times, were laid off on a south slope of open grassland on the Hopland Field Station of the University of California. There was a 3-foot alley between each replication. The plot area was fenced to keep out sheep. One group of plots was sprayed on April 22, 1965 and the other set on June 15, 1965. The grasses were beginning to head on the first date, while most plants were mature and dry on the second date. Species present on the experimental area were fescue (Festuca dertonensis (All.) Asch. & Graebn.), rattail fescue (Festuca ~ L.), broadleaf filaree (Erodium botgs (Cav.) Bertol.),redstem filaree {~rQ

The spray materials used were commercial preparations of the butoxyethanol esters of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2(2,4,5-trichlorophenoxy) propionic acid (silvex). They were applied in water at 40 gallons per acre in April and at 60 gallons per acre in June. The applications were made with a knapsack eq_uipped with a boom having three Teejet nozzles fitted with 8001 tips for the April applications and 8002 tips for the June applications. Each plot was sprayed three times to insure uniformity of the sprays on the plots. Separate control plots were used for the April and ,Tune applications.

Forage for analysis was sampled by clipping a narrow band diagonally across a plot. These clippings were placed on dry ice and kept frozen until used. Sampl~s for moisture and yield were obtained by clipping the forage on four 1-ft areas on each plot and combining the clippings. Fresh and dry weights were then determined.

The only rainfall that occurred between April 22, when the first plots were sprayed, and September 7 was on August 11, when 0.53 inches fell. All analyses in 1965 were made between the April and September dates. However, other analyses were made the following April and June. Twenty-eight inches of rain fell between September 7, 1965 and the sampling date in June, 1966.

In 1965, maximum and minimum temperatures (°F.) averaged 63 and 4o in April, 75 and 41 in May, 78 and 45 in June, 93 and 51 in July, 91 and 54 in August, and 82 and 46 in September.

Cloudiness and light intensity were not recorded. However, the skies are frequently cloudy from mid-fall through mid-spring, and mainly cloudless for the balance of the year. Thus the tests were conducted during that part of the year when photodecomposition probably was greatest.

Analyses for 2,4-D, 2,4,5-T, and silvex were done in the Agricultural Toxicology and Residue Research Laboratory, University of California, Davis. The general procedure was to macerate the tissues and then to extract the desired components with a mixture containing chloroform and a small quantity of 3 N HCl. A part of the chloroform was evaporated and the residue extracted with ethyl ether. The ehter was then evaporated, and diazomethane ' solution was added for esterification purposes. Phenoxy herbicide residues I l were determined using a Dohrmann microcoulometer as described by Bevenue, Zweig, and Nash.

Herbicides applied in April: At 24 hours after application, only about 35% of the herbicides applied were in the forage sampled (table 1). Most of the remaining 65% probably was on parts of the vegetation not sampled or on the ground.

The residues declined continuously with time, with all herbicides disappearing at about the same rate. By September 7, 134 days after application, about 99% of the original residues had disappeared. However, the residue of 2,4-D from an application of 6 lb/acre was still 23 ppm; with an application of 4 lb/acre, the residues of 2,4,5-T and silvex were 7 and 5 ppm, respectively. The losses 20.

were probably a result of photodecomposition. Crosby and Tutass found that 2,4-D decomposed rapidly in the presence of water and ultraviolet light into 2,4-dichlorophenol, 4-chlorocatechol, 2-hydroxy-4-chlorophenoxyacetic acid, 1,2,4-benzenetriol, and polymeric humic acids.

One year a:f'ter spraying, traces of 2,4-D were present in new vegetation on four of the six plots. However, 2,4-D was also present in two of the three check plots sampled at the same time. In plots sprayed the previous June, 2,4-D residue was present in 2 of-12 samples; but no residue was present in any of the check plots. The erratic occurrence of residues may indicate some carry-over of 2,4-D from the previous year in the litter. However, no residues of either 2,4,5-T or silvex were detected in any of the samples from either treated or untreated plots. ·"

Herbicides applied in June: Data for plants sprayed June 15, 1965 are shown in table 2. A study of tables 1 and 2 indicates that the phenoxy herbicides were lost faster from the dry forage than from the green forage. About 85% of the residues had disappeared in 28 days from the dry forage (table 2), while only 38% had disappeared from the green forage in 29 days (table 1). During the succeeding 28 day period there was an additional 79% loss from the plots sprayed in June and a 60% loss from those sprayed in April. It is likely that the herbicides were in a position more exposed to light on -the dry vegetation sprayed in June than on the green vegetation sprayed in April. This would make the June applications more vulnerable to photodecomposition. There is no evidence that the losses were due to volatility, because in no instance were any of the butoxyethanol esters or other ester forms of the phenoxy herbicides found in the'residues. Our results correspond somewhat to those found by Klingman et al. and Morton et al.

There was a continuous decline in the residues in dry forage with time, with 98 to 99% having disappeared by September 7, 84 days a:f'ter being sprayed. However, there was still 20 ppm 2,lr-D in the forage from an application of 6 lb/acre, and 25 and 17 ppm 2,4,5-T and silvex, respectively, from applications of 4 lb/acre. Traces of 2,4-D were present in one of six 2,4-D treated plots sampled the following April and June. However, none of the corresponding check plots had detectable residue. No residues of 2,4,5-T or silvex were found the following April or June.

In·our studies, rainfall was not an important factor influencing losses of phenoxy herbicides between the time of application and September 7, since the majority of losses occur~ed in the absence of rain. However, rainfall can be an important factor affecting losses of 2,4-D, 2,4,5-T, and dicamba from grasses.

Residues inevitably must be present in vegetation a~ter it has been sprayed. However, the presence of such residues should be viewed realistically. The residues did decrease relatively rapidly with time, but did not completely disappear from the forage sprayed in June (a:f'ter 84 days) or in April (after 134 days). However, whether residues at any time are of any real significance may b.e questioned. Certainly there is no evidence that livestock grazing even on freshly sprayed forage have been harmed in any way by the phenoxy herbicides themselves. R. ' f 21.

Table 1. Residues of herbicides in range forage at different intervals after 0 application on April 22, 1965.

Date April May May May June Sept. April 23 1965 4 11 25 22 7 5 1966

Dazs after treatment 1 8 15 29 57 134 345 Treatment Residues

3 lb/A 2,4-D ppm dry wt 572 259 125 115 65 17 o.2* lb/A 1.25 0.85 o.48 0.55 0.21 0.05 0.0003

~' 6 lb/A 2,4-D ppm dry wt 1151 719 601 347 180 23 0-34* lb/A 2.54 2-37 2-34 1.63 0.51 0.07 o.ooo6 4 lb/A 2,4,5-T ppm dry wt 631 298 299 202 217 7 o.o lb/A 1.39 0.99 1.16 0.94 0.69 0.02 o.o 4 lb/A silvex ppm dry wt 777 251 299 255 88 5 o.o lb/A 1.69 0.82 1.16 1.19 0.29 0.02 o.o

~ %water in forage 79 73 66 53 9 8 81 lb dry forage/A 2200 3300 3900 4700 3200 3000 1400

* residue of 2,4-D was found in 2 of the 3 control plots, averaging 0.11 ppm. 22.

Table 2. Residues of herbicides in range forage at different intervals after application on June 15, 1965.

Date June June June July Aug Sept April June 15 1965 22 29 13 10 7 5 1966 22

Days after treatment 0 7 14 28 56 84 264 372 Treatment Residues

3 lb/A 2,4-D ppm dry wt 663 332 126 111 31 10 o.o 0.03* . lb/A 1.35 0.71 0.22 0.21 0.05 0.02 o.o o.oooo6-·

6 lb/A 2,4-D ppm dry wt 1749 550 339 258 90 30 0.076* o.o lb/A 3.58 1.16 0.60 o.49 0.15 o.o4 0.0001 o.o

4 lb/A 2,4, 5-T ppm dry wt 1031 310 170 255 47 25 o.o o.o lb/A 2.11- 0.67 0.30 o.48 0.08 0.05 o.o o.o

4 lb/A silvex ppm dry wt 1142 218 113 114 14 17 o.o o.0 lb/A 2.33 o.46 0.20 0.22 0.02 0.03 o.o o. :

%water in forage 20 9 5 5 7 8 79 7 lb dl"'J forage/A 2050 2150 1800 1900 1700 2000 1400 2500

* Residue present in 1 of 3 replicate plots. No 2,4-D residue in control plots.

.0 ' 23.

Summary of several years studies for brush control. The following is a sunnnary of many years work conducted by Dr. Oliver Leonard on the chemical control of several brush species. While this summary" constitutes numerous trials initiated by Dr. Leonard it does not· attempt to tabularize all of the data from these trials. Much of that information is published in other sources, however. Chamise.

Striking increases in forage yields can be achieved by controlling 4 chamise on infested lands. The following table indicates this effect. Effect of control of chamise resprouts on forage yield Amount of 2,4-D Dry weight of forage per acre (lbs) i control (lb/A)

0 0 640 l 50 1,380 2 87 1,770

Chamise seedlings and resprouts are most effectively controlled by either 2,4-D or 2,4,5-T (4 lb/A). However, drought condition severely decreases the degree of control. Resprout control is enhanced by increased rates and ester formulations are more effective than water soluble forms. Neither 2,4-DP or silvex are as effective as 2,4-D and 2,4,5-T. Mature plants are less sensitive to any of the phenoxy herbicides than resprouts or seedlings. Picloram (1-4 lb/A) can effectively control chamise at any stage of growth. In addition some soil activity is evident. Karbutilate is more effective than fenuron or bromacil as soil applied applications. Interior Live oak. Interior live oak resprouts can be killed by repeated foliage applications of amine salts or esters of 2,4-D, 2,4-DP, 2,4,5-T or silvex. The best control is obtained when the subsoil is sufficiently moist to allow root growth, but following the period of rapid shoot elongation. Late fall to early winter applications have proven most effective. Control during winter and early spring can only be obtained when the resprouts have not lost too many leaves from frost or other causes. Although excellent control can be obtained with amine salts, esters are more consistent. Control is strikingly associated with rate with 4 lb/A being required in most cases. 24.

Excellent control of interior live oak is essentially never obtained by a single application. Therefore, one should expect to make from 2 to 3 reapplications,one each year.

Repeat applications of a phenoxy herbicide is more important than the chemical used. However silvex generally appears to provide the best control.

Interior live oak was never completely controlled by aircraf't applications. Incomplete coverage is believed to cause this effect. Repeat applications with either mist blower or ground sprayer are more effective.

Control by a single application is readily obtained with basal, cut­ surface, or stub treatments. However, control is sometimes less than 100%. 2,4-D + 2,4,5-T, 2,4,5-T, or silvex in diesel oil are most effective as basal sprays. 2,4-D amine applied to cuts in the stems or to the tops of freshly cut stumps can achieve high degrees of plant kill.

Canyon Live oak and Tan Qak.

Statements that were made about Interior live oak control also apply to tan oak and canyon live oak. However in one study a single a~plication of 2,4-D amine indicated a strong dose relationship ori canyon live oak. A rate of 16 to 32 lb/100 gal. of spray gave close to 100% control (October application). The same result did not occur with tan oak.

Mountain misery (bear-mat). No single application of any herbicide to the foliage of mature mountain misery gave more than 50% control. However, a repeat application in June a year later resulted in a high degree of plant kill with 2,4-D amine or ester.

The importance of reapplication greatly exceeded that of rate in these tests. In contrast regrowth can be killed readily if properly timed. Mountain misery is most sensitive to phenoxy sprays the year following fire or mechanical removal but timing of the spray application is critical. If sprayed too early, many non-emerged sprouts will be missed. Mid-June to mid-July is probably the best period. 2 lb/A of 2,4,5-T has given 100% kill followin& fire, but it was less effective following mechanical removal. However, 3 lb/A of 2,4-D gave 90'/o kill and 6 lb/A a kill of 97%• Regrowing mountain misery was still very sensitive to 2,4,5-T two and three years a:rter burning. Kills of 80 to 100% can be obtained with 2 to 4 lb. of 2,4,5-T per acre applied from mid-June to mid-July; a kill of 80% was obtained with 4 lb/A in March, but kills were zero in October. Regrowth mountain misery was 90% controlled with 1 lb/A picloram applied in June, while a 4 lb/A rate gave 100% kill, or nearly so, at all seasons. Po_nderosa Pine and Incense Cedar Selectivity.

Ponderosa pine seedlings following a fire were 10o% controlled with 2,4,5-T one year later. However later evaluation revealed many pine seedlings in the sprayed area. It is believed that these came up the fall following the spraying.

Incense cedar seedlings, in contrast to Ponderosa pine; are tolerant to 2,4,5-T and there is now a forest of incense cedar on these plots. Most of the ponderosa pine survived 1 or 2 lb/A 2,4,5-T applied in late

\.J June or later the second or third year after the fire. Most seedlings also survived at 4 lb/A. when applied in late July •. Apical buds were killed however. Eleven years later these effects were not evident. To minimize bud damage, spraying must be delayed until late July or August and a dose· used that does not give the best control of mountain misery or other shrubs. Picloram (1 lb/A) gave good control of mountain misery and deerb:rush in June, while only damaging the buds of Ponderosa pine. The pine recovered and the sprayed trees were not identifiable a:rter 4 years. The 1 lb/A picloram at other periods of the year gave less pine injury, but the brush control was not satisfactory. · Incense cedar was injured far more than Ponderosa pine by picloram. Ponderosa pine seedlings observed the fall and winter following a spray application of 2,4-D, 2,4,5-T, or silvex were undamaged by residues from these mat~rials.

Poison oak. Poison oak is most sensitive to foliage applied herbicides after the rapid rate of spring growth has subsided but before the plants have become drought stressed. 2,4-D (4 lb/A), 2,4,5-T ( 4 lb/A), silvex (4 lb/A), and picloram (1-2 lb/A) can be used to control poison oak. Considerations on which herbicide to ,. use are speed of control, number of retreatments, safety to surrounding I i vegetation, and cost of the herbicide.

I [: 2,4-D, 2,4,5-T and silvex seem most economical; however, two or more retreatments at yearly intervals are required to achieve complete control. Silvex is the most effective of these herbicides. 26.

Control of poison oak with amitrole, or picloram, is related to rate. Even though a high degree of poison oak control can be achieved by a single high rate of one of these herbicides, eradication can only be achieved by follow-up treatments.

Resprouts are generally easier to control with phenoxy herbicides than old plants but it is essential to choose the right stage of growth to obtain this effect. Poison oak in the open is o:f'ten more sensitive to the phenoxy herbicides than are those plants that are in the shade. Basal applications are useful for controlling poison oak but they usually do not completely kill the plants; root sprouts will have to be controlled later. Soil treatments of picloram (4 lb/A) karbutilate (16 lb/A), borax + monuron '(400 lb/A), and borax (800 lb/A~ have been ineffective against poison oak.