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Division of Agricultural Scie

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UNIVERSITY OF CALIFORNIA

is bulletin lists chemicals used for controlling woody plants, and describes application equipment and methods of applica- tion. Problems involved in control are discussed and solutions are given. Tables showing reactions of woody plants to chemical treatment are also included.

CALIFORNIA AGRICULTURAL EXPERIMENT STATION

BULLETIN 812

CHEMICAL CONTROL OF WOODY PLANTS

WARNING ON THE USE OF CHEMICALS AND RULES FOR SAFE USE

Herbicides vary in toxicity to man and other animals but all should be used with care. The following sug- gestions for the use and handling of herbicides will help minimize the like- lihood of injury, from exposure to such chemicals, to man, animals and crops, other than the pest species to be con- trolled.

Always read all precautionary label- ing directions before using herbicides and follow them exactly. Notice warn- ings and cautions before opening the container. Repeat the process every time, no matter how often you use a herbicide, or how familiar you are with the directions. Apply material only in amounts and at times specified.

Keep herbicides out of reach of children, pets, irresponsible persons, and livestock. They should be stored outside the house, away from food, feed and seed, and under lock and key.

SPECIAL MATERIAL

Always store sprays and dusts in their original containers and keep them tightly closed. Never keep them in anything but the original container.

Never smoke, eat or chew while spraying or dusting.

Avoid inhaling sprays or dusts. When directed on the label, wear pro- tective clothing and a proper mask.

Do not spill herbicides on the skin

or clothing. If the liquid concentrates are accidentally spilled, remove con- taminated clothing immediately and wash the contaminated skin thor- oughly.

Wash hands and face and change to clean clothing after applying herbi- cides. Also wash clothing each day before re-use.

If symptoms of illness occur during or shortly after dusting or spraying, call a physician or get the patient to a hospital immediately.

Cover food and water containers when treating around livestock or pet areas. Do not contaminate fish ponds, streams, or lakes.

Always dispose of empty containers so that they pose no hazard to humans, animals, valuable plants or wildlife.

Observe label directions and follow recommendations to keep residue on edible portions of plants within the limits permitted by law.

Do not use the mouth to siphon liquids from containers or to blow out clogged lines, nozzles, etc.

Do not spray with leaking hoses or connections.

Do not work in the drift of a spray or dust.

Confine chemicals to the property and crop being treated. Avoid drift to adjoining property and crops by stopping treatment if the weather con- ditions are not favorable.

MAY, 1965

The Authors:

O. A. Leonard is Lecturer and Botanist in the Experiment Station, Davis; W. A. Harvey is Agriculturist in the Agricultural Extension Service, Davis.

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Chemical Control of Woody Plants

JLhe following control recommendations are based upon research investigations carried out by the University of Califor- nia personnel in the Agricultural Experi- ment Station and Agricultural Extension Service in cooperation with the State De- partments of Agriculture and Public Health, the United States Department of Agriculture, and the agricultural and chemical industries.

These recommendations have been de- veloped on a statewide basis, but special problems of control in local situations have been noted and in these instances recommendations apply only to the area designated. Controls for the major prob- lems are given, but these problems may not be present in every area. Use the recommendations applicable to your area.

IN early one-half of California's land is covered with woody plants, and about one-third of this cover is brush and non- commercial forests now of little economic value. Some of this land is suitable for conversion for range and crop purposes, other areas may be cleared for water- sheds, and still others will eventually be

partially cleared for rural living and rec- reation. Fairly large areas not appreciably altered by man will likely remain, espe- cially within national and state park and wilderness area boundaries.

Slightly over one-sixth of California is covered with commercial coniferous for- ests whose productivity cannot be main- tained without effective measures for re- foresting burned-over areas and increas- ing the productivity of the rest. Herbi- cides can perform a valuable function in timber production, as losses from forest fires can be reduced by construction of effective fuelbreaks made by chemical removal of underbrush and unwanted trees along ridge tops.

Herbicides properly used can perform an important function in controlling un- wanted woody plants, such as poison oak, while leaving those that are desirable. California can be made a better place to live by landscape improvement and by minimizing the destructiveness of chap- arral and forest fires.

Tables detailing preparation and use of herbicides discussed in text will be found at the back of this publication.

NOTE: See pages 5 and 16 for further precautions on use of chemicals.

EFFECTIVE CHEMICALS

The chemicals most effective for con- trolling woody plants are:

2,4-D, 2,4,5-T, silvex, AMS, amitrole, fenuron, fumigants, picloram, dicamba, and cacodylic acid.

2,4-D and 2,4,5-T (2,4-dichlorophenoxy- acetic acid, and 2,4,5-trichlorophenoxy- acetic acid) are commonly used for con- trolling woody plants of many different species. 2,4,5-T controls a greater num- ber of species of woody plants than 2,4-D but each of the chemicals listed is more

effective on certain plants. Since most brush areas are composed of several species, mixtures of 2,4-D and 2,4,5-T called "brush killers," are commonly used; both of these compounds appear to affect woody plants in the same basic manner. Radioactive tracer tests indicate that 2,4-D is absorbed by leaves in greater amount than 2,4,5-T, but also indicate that 2,4,5-T is more stable in plants. Rel- ative effectiveness of the compounds varies with plant species, and with time and method of application.

1 Submitted for publication November 20, 1963.

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These herbicides are available in sev- eral different formulations. The most commonly used and satisfactory formula- tions for brush spraying are the "low vol- atile" esters: butoxyethanol, propylene glycol butyl ether, and isooctyl. Although termed low volatile, their volatility makes them unsafe for use near susceptible crops, such as vineyards, especially when high temperatures prevail. (A much more volatile formulation of the butyl ester is often used on big sagebrush where there is no danger to adjacent crops.)

Special formulations of esters of 2,4-D and 2,4,5-T are used to reduce drift, par- ticularly from air application. These make a so-called invert emulsion, which is a thick mayonnaise-like (water in oil) emul- sion forming large drops or particles when sprayed. Thickness of the emul- sion can be varied by changing the ratio of oil and water.

Water-soluble amines are the most ef- fective of the various formulations for killing trees by the cut- surface method, and are sometimes used for controlling brush, especially where volatility is a haz- ard. Amines are essentially nonvolatile, but are not as effective as esters when used as foliage sprays on established brush species.

Oil-soluble amine formulations are generally more effective than water- soluble amines when applied as foliage sprays, but are less effective than esters. Essentially nonvolatile, they may be used in place of esters when nonvolatility is desired.

Acid formulations have low volatility but are more volatile than the amines. Acid formulations, generally less effec- tive than esters, are used where low vol- atility is important.

Silvex (2(2,4,5-trichlorophenoxy)propionic acid), a compound similar to 2,4,5-T, is sold as water-soluble amine and low-vol- atile ester formulations. Silvex is more effective than 2,4-D or 2,4,5-T in control- ling certain woody plants such as live oak, salt-cedar, poison oak and blackberries.

AMS (amonium sulfamate), an inorganic herbicide used for controlling a wide variety of woody plants, is more effective

where high humidity and fog are present. AMS can be used with relative safety near growing crops and ornamentals. It is soluble in water and is applied as an aqueous spray containing a wetting agent or emulsifiable oil.

Amitrole (3 amino- 1,2,4-triazole) is a water-soluble herbicide that induces chlorosis (yellowing or blanching of nor- mally green parts) in plants. Results are more consistent when a small quantity of sticker-spreader or household detergent is added to the spray mix. Amitrole is used widely on poison oak, and also may be used on black locust, many species of Rubus, and elm. Cut-surface treatments have shown no promise except on big-leaf maple in the spring.

Fenuron (3-phenyl-l,l-dimethylurea) is applied to the soil in the form of pellets and absorbed by the roots.

Fumigants are especially useful for quick control of woody plants. Effective fumi- gants include DD® (1,3-dichloropropene and 1,2-dichloropropane mixture), Te- lone® (principally 1-3-dichloropropene), EDB (ethylene dibromide), and SMDC (sodium N-methyl dithiocarbamate).

Picloram (4-amino-3,5,6-trichloropicolinic acid) is a new herbicide. Spray mixtures of picloram and other herbicides will probably be used, as picloram is not ef- fective against all brush species and ap- pears to be slightly more damaging to grasses than 2,4-D. Forty pounds per acre of 10 per cent picloram pellets were effec- tive in controlling chamise and mountain misery in a test conducted in 1963. The results on toyon, canyon live oak and Cali- fornia black oak were much less favorable. Good control of chamise, mountain misery, whiteleaf manzanita, Ceanothus, creeping sage, and periwinkle was ob- tained with 4 pounds of picloram (potas- sium salt) per acre applied as a foliage spray; 1 pound per acre was adequate on some of these species. Good control of poison oak has been obtained by high volume leaf-stem spraving, but control with a similar quantity of picloram ap- plied at 20 gallons per acre or with the mist blower was less complete. Foliage sprays gave only poor control of interior

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live oak and toyon. High volume sprays appear more promising at this time than does low volume application.

Picloram applied to cuts in trees shows considerable promise; present evidence indicates that good results may be ob- tained using a wider spacing of the cuts than is possible with 2,4-D amine. Pic- loram appears to be very mobile in some woody plants, especially in madrone, California buckeye, and California laurel.

Picloram can injure desired species of woody plants by being picked up by the roots following application to the soil.

Recommendations for use of picloram cannot be made now as adequate data are lacking, but the above mentioned re- sults should serve as a guide in testing programs.

Dicamba ( 2-methoxy-3,6-dichlorobenzoic acid) appears to produce plant reactions similar to picloram but is less effective. Preliminary data indicate that it is effec- tive against chamise, Ceanothus, and ma- drone.

Dicamba, as well as picloram, is more stable in soil and probably is more stable in plants than are phenoxy herbicides. (Mixtures of dicamba and phenoxy herbi- cides will probably be used for woody- plant control.)

Cacodylic acid (dimethyl arsinic acid) shows promise for early thinning in stands of conifers when applied to cuts in the trunks. It can also be used as a contact spray for killing back shoots of unwanted woody plants.

PRECAUTIONS IN THE USE OF CHEMICALS FOR WOODY-PLANT CONTROL

2,4-D, 2,4,5-T, and silvex are growth- regulatory-type weed killers and can cause injury to nearby plants by volatility and spray drift. In California, a use per- mit from the County Agricultural Com- missioner is required in order to pur- chase more than /2-pound of chemical per day. Do not use the same equipment for applying fungicides and insecticides, since it is difficult to remove all traces of the herbicides from sprayers.

AMS is corrosive to spray equipment, which should be washed immediately after use.

Fenuron will cause chlorosis on shrubs or trees having roots beneath the point of treatment. Washing (as from heavy rain- fall) may cause injury to grass some dis- tance from the point of application.

Fumigants are poisonous and cause severe blistering if allowed to remain on the skin. If these materials are splashed on the skin, they should be washed off im- mediately with soap and water. If spilled on clothing or shoes, these garments should not be worn again until the articles are cleaned or washed.

Amitrole should be used with caution on rangeland. Remove all livestock before treatment and do not graze or plant to forage crops for 8 months after treatment.

APPLICATION METHODS

1 he degree of control of most species of woody plants growing in California is de- termined by the amount of herbicides applied; this appears to be true for all methods of application: foliar and basal sprays, cut-surface applications on stems, and stump and soil treatments. Where chemical cost, selectivity, and residues are not important considerations, increas- ing the dosage usually increases the con- trol. Regardless of dosage, however, many

species of plants will require re-treatment for complete control (especially with fo- liage spray treatments).

FOLIAR SPRAYING

In foliar spraying, leaves and stems are covered with the sprav solution, and spraying must be done at the proper time. Deciduous woody plants, such as poison oak, should be sprayed during the grow- ing season after most leaves have fully

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enlarged, and spraying can be continued as long as plants are growing. Woody plants are much less sensitive to sprays when growth stops due to exhaustion of soil moisture, and many of them require as much as three annual applications for satisfactory control.

Woody plants sprouting from crown or root are most effectively controlled by treating sprouts after a fire or after cut- ting. Brush and forest fires are an annual occurrence in California; therefore, spray programs should be planned ahead so as to be immediately available following fires. The best time to spray burned areas is the first or second spring following the fire. Another important advantage of spraying after a fire is that much of the fuel has already been consumed and dead brush resulting from spraying does not appreciably increase fire hazard.

Individual plant treatment with ground equipment is necessary when broadcast methods are not effective, when bushes are scattered, or when selective control of individual plants is desired.

It is important to spray all parts of the plants, including the lower leaves and stems, because most herbicides are not translocated (moved within the plant) effectively over long distances. Movement of the herbicide into the crown and roots is increased by thorough coverage of the lower leaves and stems.

Brush killer. Use 4 pounds of acid equiva- lent of an equal mixture of 2,4-D and 2,4,5-T (low-volatile esters), 1 gallon of diesel oil, and water to make 100 gallons of spray mixture. Apply with conventional spray equipment with agitation; for a back-pack mist blower, use the same amount of chemical and oil and water to make 4 to 8 gallons of spray mix. Use the same quantity of chemical, diesel oil, and water for making spray mixtures with silvex. Diesel oil usually increases the effectiveness of the sprays and helps to make the sprayed woody plants visible, especially when a back-pack mist blower is used.

AMS. Use 75 pounds of chemical, make to 100 gallons with water, and add 8 ounces of sticker-spreader (an effective

spray is made by replacing 10 gallons of the water with 10 gallons of an emul- sifiable oil). AMS solutions can be applied with conventional sprayers.

Amitrole. Use 5 pounds of amitrole to 100 gallons of water plus 8 ounces of sticker-spreader.

Over-all spraying with ground equipment, using brush killer or AMS, is often used if there are too many plants to spray in- dividually.

Brush killer. Use 4 pounds of an equal mixture of 2,4-D and 2,4,5-T (low-vola- tile esters), M-gallon of diesel oil, and water to make 40 gallons. Apply this volume per acre with a conventional sprayer equipped with a spray boom. The same quantity of chemical can be applied in a much lower volume (5 to 10 gallons) with a mist blower. Excellent re- sults have been obtained with 5 to 10 gallons per acre applied with the back- pack mist blower.

AMS. Use 75 pounds of AMS, 10 gallons of emulsifiable oil and sufficient water to make 50 gallons per acre. This spray can be applied with a mounted mist blower or conventional spray equipment with spray boom.

Aircraft application is useful for treating large areas, especially those difficult to spray with ground equipment. Use brush killer and oil mixture as above, but add only enough water to make 5 to 10 gal- lons of spray — using the lesser amount for burned-over areas.

Invert emulsions are applied to rights- of-way by centrifugal sprayers mounted on helicopters; this keeps sprays largelv confined to the desired strip. Drift is not eliminated but it is far less than when a normal emulsion is applied bv spray booms. Use 6 to 12 pounds acid equiv- alent of a mixture of 2,4-D and 2,4,5-T in diesel oil and water to make 12 to 20 gallons per acre. The ratio of diesel oil to water affects the viscosity of the invert spray mixture; viscosity is increased as the percentage of water in the mixture is increased. Where minimum drift is de- sired, minimum diesel oil to make a flow- able emulsion should be used; however,

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1. Back-pack mist blower. (Photo courtesy Alva G. Neuns.)

such spray mixtures lose some of their effectiveness. Width of spray swaths from the helicopter can be varied from 20 to 50 feet.

BASAL SPRAYING

In this method, chemicals are applied in diesel oil to lower parts of the stems of woody plants. Best results are obtained when soils are neither excessively wet or dry; winter and spring applications are generally satisfactory, although good re- sults have been obtained in forested areas with late spring and summer applications. 2,4,5-T is more effective than 2,4-D for controlling woody plants by this method, but an equal mixture of these two com- pounds approaches 2,4,5-T in effective- ness and for economy brush killer is recommended.

Brush killer. Use 16 pounds of an equal mixture of 2,4-D and 2,4,5-T (low-volatile esters) in sufficient diesel oil to make 100 gallons of spray mixture. Cover all sides of the stems near the ground line, using a solid-cone spray, and apply 2 to 3 fluid ounces of mixture for each inch of stem diameter — enough to have runoff at the base of plant. The method is most useful on stems up to 2 inches in diameter; larger stems should be frilled or cut into near the base and the spray also applied to cuts.

CUT-SURFACE TREATMENT ON TREES

This treatment is effective for controlling unwanted trees. It is more selective than and treatments can be made

spraying

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throughout the year, but it is usually most effective from late fall through early sum- mer. There is no spray-drift problem.

Deep cuts are made near ground-level with a heavy hatchet or axe. Each cut should be horizontal, to retain applied chemicals, and cuts should be close to- gether (on vigorous sprouting species such as live oak it is best to make a complete girdle). Undiluted 2,4-D amine (water soluble) should be put into the cuts, using a pump oil-can or polyethylene squeeze bottle. Use about 1 milliliter of amine for each inch of stem diameter; a 14-inch tree should receive about Yz fluid ounce. 2,4,5-T amine is also effective but is more expensive than 2,4-D amine; it should be used on maples, however.

Several mechanical injectors for making cut-surface applications are available. Some models automatically release a squirt of chemical at each cut; others have a trigger arrangement which must be tripped. (A disadvantage of the auto- matic-release type is that insufficient chemical may get into the cuts.) Cuts, or jabs, must be close together and deep enough to penetrate into the wood. Amines are easier to inject when diluted with an equal quantity of water, but fur- ther dilution with water is undesirable as the quantity of solution must be increased to compensate for increased dilution.

Injections of esters in diesel oil give good results if cuts are filled with the mix- ture; diesel oil makes esters flow more readily and helps lateral movement. Volume per cut should be increased as the concentration of the chemical is re- duced. A recommended mixture consists of 4 pounds acid equivalent of an equal mixture of 2,4-D and 2,4,5-T esters made to 4 gallons with diesel oil. Esters are not as effective as water-soluble amines in preventing sprouting.

STUMP TREATMENTS

Stumps may be sprayed with the basal spray mixtures described. Stumps and bases of all sprouts, and all small sprouts, should be thoroughly sprayed. Effective-

ness of treatment is increased by cutting into stumps near the base, and control is best when stumps are treated immediately after felling the trees. Such stumps may be treated with 2,4-D amine (water soluble) applied liberally to the tops of the stumps and in cuts close to the ground; winter is the best season for treatment. Water- soluble 2,4,5-T amine should be used on stumps of maple. AMS crystals placed on stump-tops are also used to control sprout- ing, but are less effective.

SOIL TREATMENT

Fenuron is the only herbicide of impor- tance now being used in soil application for controlling woody plants (see results with picloram pellets, page 4). It is marketed in the form of pellets containing 25 per cent actual fenuron. Applications should be made at base of the stems, from November through January under Cali- fornia conditions. It is most effective on granitic and sandy soils. It has proved effective on live oak, blue oak, toyon, coffeeberry and other chaparral species but has given poor kills of poison oak. Three ounces should be placed at the base of each cluster of live oak stems; a large clump may have several stem clusters and thus may require as much as a pound of pellets. Bushes die over a period of 3 years or more. Although the chemical is expensive, application is easy and in many cases no re-treatment is necessary.

Soil fumigants are useful for killing individual woody plants and have been effective against poison oak, blue oak, live oak, walnut and grape rootstocks: Killing is most rapid during periods of greatest growth. Use Vk fluid ounces of a soil fumigant (such as DD®) per hole 6 to 8 inches deep, spaced about 6 inches apart around base of the plant. Roots are normally killed about 10 inches from the point of application but have occasionally been killed as far away as 30 inches. Care should be taken when treating close to desirable plants, as their roots might be damaged.

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2. Live oak regrowth controlled with fenuron pellets.

APPLICATION EQUIPMENT

I

Ihe major considerations when select- ing equipment are availability, efficiency, selectivity, and amount of spray drift. Mechanical agitation in the spray tank is essential when emulsions of 2,4-D, 2,4,5-T, and silvex are used.

Back-pack knapsack and compressed air sprayers. Commonly used for treating in- dividual woody plants.

Back-pack mist blowers. Useful when a small volume of spray mixture, or speedy application in a small area, is needed. Sprayers should be equipped with a quick shut-off valve near the opening where spray mixture enters the air-stream, and the orifice-opening should be adjustable at this same point. Allowance must be made for spray drift when using this equipment.

Power sprayers. Used for spraying indi- vidual woody plants and for broadcast spraying. For hard-to-reach areas, side hoses may be attached to the main hose- line (pneumatic-type couplings facilitate operations). Spray booms or offset nozzles on mobile sprayers are sometimes used for spraying roadsides or fields of brush.

Mounted mist blowers. Useful in areas where tractors can operate.

Helicopters and airplanes. Helicopters have largely replaced the airplane for broadcast spraying, except on more easilv accessible areas. Difficult areas can be flown over successfully and relatively safely with a helicopter, and small clear- ings can serve as heliports. Spray drift is a problem in aircraft spray-application, but attempts are being made to minimize it through development of proper spraying devices.

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WOODY PLANT CONTROL

RANGELAND PROBLEMS

Coyotebrush, California sagebrush, and sages are controllable by aircraft spray- ing with 2,4-D. Soil moisture should be sufficiently high for good plant growth. Poor control will result if the plants are not growing vigorously. To control these plants, 4 pounds of 2,4-D (water-soluble amine) per acre is recommended; the spray mixture should contain ^-gallon of emulsifiable oil and water to make 10 gallons. Where sages are present, an ester formulation in place of amine, and diesel oil in place of emulsifiable oil, should be used.

For coastal brush containing black- berries, poison oak, and other sprouting species, use the brush-killer mix suggested for over-all spraying (page 6). Sprayed areas should be burned in the fall follow- ing spraying, and brush regrowth should be ground-sprayed the following summer. Grazing helps control brush regrowth.

Chamise control should be initiated after a fire by seeding burned areas with the grass desired. Regrowth can be con- trolled by using ground equipment the first or second year after a fire. A brush- killer mixture of 2,4-D and 2,4,5-T is sug- gested, but 4 pounds of 2,4-D ester per acre usually gives a comparable kill. Under unfavorable conditions more than 4 pounds of herbicide per acre increase the kill. The best period for spraving in the first year after the burn is from late April through May, and from March through May in the second year. Chamise is controllable by individual plant treat- ment from December through June, but soil moisture must be adequate for shoot and/or root growth. Plants surviving the first chemical application can be con- trolled by re-treatment.

Chamise regrowth can also be con- trolled by aircraft spraying during the first spring after a fire, using the same herbicides as above and a spray volume of 5 gallons per acre. Timing is critical: plants should have sprouted but regrowth over 10 inches tall is often hard to kill

with a single spraying; excessive growth following rainy periods, or insufficient growth due to drought, reduces effective- ness of sprays.

Good to excellent control of chamise with one application is obtained 50 to 60 per cent of the time. When good control is not obtained with one application sat- isfactory control is normally achieved with one or two annual re-treatments. An additional advantage of re-treatment is that many of the other sprouting species present require repeat applications for control (sprouting manzanita, toyon, poison oak). Nearlv all brush seedlings are killed bv aircraft treatment, but new seedlings may develop where grass is sparse or nonexistent. When good con- trol of chamise and brush seedlings has been obtained, the remaining plants are best controlled by individual plant treat- ment.

Grazing is important in converting chamise-covered areas to grass and in maintaining the conversion. Perennial grass and clovers are highly desirable as they help control brush and weeds. On areas where grass grows poorly a certain amount of spraying is necessary to pre- vent return of brush.

Shrubby vegetation (often spoken of as "chaparral") is widespread in California, and is comprised of manzanitas, Ceano- thus, shrub oaks, chamise, and other predominately evergreen shrubs. Areas needing control should be crushed (if pos- sible), burned, and seeded to grass. Spray- ing should begin the following spring (as with chamise), although the date of spray application should be slightly later to allow time for sprouts to develop. At least 4 pounds of brush killer per acre should be used, and more than one re- treatment must be made for good control. Unwanted plants remaining after three annual aircraft applications should be given individual treatment (shrub oaks are the most difficult to control). Grazing helps greatly in achieving and in main- taining control.

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, ■

3. Dense chaparral converted to grass by burning, seeding, and spraying. Note smal

untreated plots on left

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Woodland and woodland-grass areas may be converted to grasslands by using individual plant treatments. It is advis- able that trees be felled in winter and the stumps treated with 2,4-D amine (see Stump Treatments, page 8). Treated areas should be burned after about Vk years and then seeded to grass. Grazing does much to control brush regrowth, but a back-pack mist blower can be used where needed.

Trees can also be treated by the cut- surface method, preferably during winter or spring, using 2,4-D amine. Such plants as understory poison oak, and coffeeberry, are "released" and grow better because of treatments — they can be sprayed with a back-pack mist blower. Grass growth beneath treated trees is usually markedly increased. Burns should not be made for several years in order to allow dead trees to fall and furnish fuel for a good burn.

Two or three annual individual plant

treatments are usually needed to control sprouts which develop abundantly on oak woodlands that have been burned, or bulldozed and burned. Oaks are con- trolled with difficulty, so all parts of them should be carefully covered with spray. Sprouts of interior live oak, blue oak. and poison oak are more sensitive to silvex spravs than to either 2,4-D or 2,4,5-T. Where interior live oak and blue oak are present in limited numbers, fenuron pel- lets may be more economical than sprays because of reduced labor costs. Two ounces of pellets per clump may be used on blue oak, and three ounces on live oak. Big sagebrush and green rabbitbrush are controllable with esters of 2,4-D. Big sagebrush is the dominant shrub on large areas of California range; green rabbit- brush is dominant or important only on limited areas. Range grasses respond quite favorably when released from com- petition with these shrubs.

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Big sagebrush can be controlled by aircraft spraying of 2 pounds of 2,4-D per acre, with /2-gallon of diesel oil and water to make 5 or 6 gallons of spray. Spray should be applied when plants are growing vigorously and the first new leaves are as large as the old leaves.

Green rabbitbrush is deciduous and is sprayed at a later date than big sage- brush. Spraying should begin after the new twig growth has attained an average length of 3 inches; spraying can continue as long as there is enough soil moisture for vigorous growth. A single application of 3 pounds of 2,4-D ester per acre, with ^-gallon of diesel oil and water to make 5 or 6 gallons of spray, controls about 80 per cent of the plants. A good kill of big sagebrush and green rabbitbrush can be obtained by spraying with 3 pounds of 2,4-D per acre at this time.

FOREST AND

REFORESTATION

PROBLEMS

Chemical control of undesirable woody plants, either trees or brush, can be of value on forest lands as well as on range lands, and commercial use of herbicides in reforestation programs in California has been increasing since 1954. The growth of desirable forest trees can be speeded either on seeded areas or in natural stands by removal of competi- tive growth and by careful manipulation of the vegetation. Although undesirable woody species may be similar on range and on forest land, the objectives of con- trol are different. Maximum tree growth requires a reduction in competition for both light and moisture. Grass is not de- sirable because of competition and be- cause it is attractive to wildlife (particu- larly deer) and livestock which damage small trees.

Fortunately, conifers are moderately resistant to 2,4-D and 2,4,5-T except when the shoots are growing. In general, 2,4-D is more damaging to conifers than is 2,4,5-T.

Spraying after burning or mechanical clearing should be done as soon as pos- sible to achieve quicker planting, to allow less time for grass to become established,

and to best control brush seedlings and sprouts. A burned-over area provides favorable conditions for sprout develop- ment and establishment of grass — and these attract deer and other wildlife detrimental to young Douglas fir. Areas covered with chemically killed brush, however, are neither as accessible nor as attractive to deer as are burned areas. Broadcast spray applications should be made between June 15 and August 15. Mountain misery, brush seedlings, and broad-leafed weeds are most readily con- trolled following this plan. Trees can be planted in the winter or spring following spraying. Better plant kills are likely to be obtained — and this is an important consideration for areas where an appre- ciable investment will be made in plant- ing.

Newly established plantations or young natural seedlings of Ponderosa pine can tolerate 1 pound of 2,4,5-T per acre soon after shoot growth stops in the summer; tolerance increases rapidly so that the small pines can usually withstand 2 pounds of 2,4,5-T per acre after mid- August. Pines 5 or more years old appear slightiy more tolerant to sprays than do younger trees. Mist-blower sprays are more damaging than sprays applied with a boom. Pines may become slightly more sensitive to autumn sprays if early autumn rains occur.

Established stands of conifers may often be released by controlling com- peting vegetation. Conifers in the im- mediate vicinity of trees treated by the cut-surface method show a growth in- crease; this may develop within 2 years after treatment.

Dormant sprays applied by helicopter on madrone and tan oak are most effec- tive when applied between mid-March and bud-break of the Douglas fir. It is suggested that 3 pounds acid equivalent of an equal mixture of 2,4-D and 2,4,5-T esters be applied, either in sufficient diesel to make 10 gallons of mix per acre, or as an emulsion using 1 gallon of diesel and water to make 10 gallons of spray per acre. A second application will be re- quired in a few years. Some of the madrone is killed by these treatments, and tan oak is severely damaged. Re-

[12]

covery of these trees is slow, which gives the conifers an opportunity to grow. Un- derstory grand fir, hemlock, and western cedar benefit from the spraying, even though sprays may cause injury. Re- covery normally requires 1 to 3 years.

Dormant sprays should be applied on the deciduous species of red alder and vine maple when buds of these species are breaking. The spray mixture consists of 2 pounds of 2,4,5-T (ester) in 9£ gal- lons of diesel oil per acre. In such treat- ments, alders 8 inches or less in diameter are often killed, but vine maple is top- killed only. Other associated species (bay, madrone, chinkapin, snowbrush ceano- thus, cascara) are top-killed; sprouting is vigorous on snowbrush ceanothus and cascara following treatment. It is not yet known whether a single spraying will sufficiently release conifers when the lat- ter two plants are the dominant species present.

Proper helicopter spraying on Douglas fir in summer causes little damage to this tree after shoot elongation has ceased. A

treatment consisting of 1/2 pounds of 2,4,5-T ester in J2-gallon of diesel oil, with water to make 8 gallons per acre, gives moderate control of blueblossom ceano- thus, snowbrush ceanothus, and cascara. Some commerical spraying is done during the period of shoot growth of the Douglas fir in order to achieve better brush con- trol— but tree injury suggests that this period should be avoided if possible.

Tall trees and snags make helicopter application unsafe and good application by any means impossible, so they should be felled prior to spraying. Stumps of sprouting species should be treated to reduce or prevent sprouting. Areas to be treated should have an adequate stand of understory conifers.

SPECIAL PROBLEMS

Wild currants and gooseberries (Ribes spp.) are alternate hosts to the white pine blister rust which has been so destructive to white and sugar pine in northern Cali- fornia. Individual plant treatments are re- quired for control (table 1).

4. Fuel breaks can be attractive as well as useful. Woody growth was cut and burned, sprouts and seedlings were sprayed, and the area seeded to grass. (Photo courtesy California State Division of Forestry.)

Fuel breaks — cleared paths located on woody or brushy ridges and elsewhere — are important in controlling fires. They are of two types. One type is produced by removing all woody growth on the breaks, and is common in chaparral areas. The other type of break is used in wooded areas, and is produced by removing dense stands of understory brush and some trees.

The best time to develop a fuel break in chaparral is after a fire, since most of the fuel is consumed at this time and the new sprouts and seedlings are more easily controlled than the old brush. In southern California helicopters are used to spray wide strips in order to prevent re-estab- lishment of a brush cover. Dosages for such sprays are normally twice that used on range areas, and two or more appli- cations are made at yearly intervals. Back-pack mist blowers and fenuron pel- lets may be used in the final cleanup of breaks. Grass establishes naturally on breaks and retards the re-establishment of brush. Grazing of breaks helps prevent return of brush cover.

The use of brush-free breaks in wooded or forested areas should be greatly expanded. Shrubs and dense stands of small trees should be removed to create a park-like effect. Trees and grass help prevent return of brush under- story, and limited spraying will help maintain the breaks.

Fire hazard reduction around homes and buildings in brushy areas is often of vital concern. Widely scattered native shrubs and trees should be left for land- scape purposes, and their natural adapta- tion to a site is an important considera- tion in landscaping. Unwanted woody plants can be controlled by methods al- ready described. Keeping dry grass at a minimum helps control fire, and this can be aided by grazing. Where this is un- desirable, grass should be reduced by mowing or chemical treatment. Most native woody plants can tolerate a low dosage of a combination of simazine, amitrole, and 2,4-D applied to the soil in winter.

Water supplies often can be increased by controlling woody plants around

5. Fire hazard around dwellings can be reduced by removing most of the brush. Attractive

shrubs can be left for landscaping.

6. Poison oak control in coastal live oak woodland. Photos show an area (left) before control was started, and an area (right) after control was achieved.

springs and streams, and there is evidence that water yields may be increased on watersheds by substituting grass for woody growth (it is often desirable to leave a few shrubs and trees for scenic effect). Watersheds should be grazed to reduce fire hazard and to help prevent reinvasion by woody plants.

Stream beds are often clogged with woody growth which restricts water flow and may use quantities of water. Such woody growth can be controlled with amine forms of 2,4-D and 2,4,5-T applied in spring and summer. If it is necessary to delay spray applications until mid-fall, ester sprays containing 10 per cent diesel oil should be used.

Good control of willows and cotton- wood has been obtained with AMS in the Salinas Valley, where the use of 2,4-D and 2,4,5-T is hazardous. The control achieved in this area was probably aided by foggy conditions which enhance ab- sorption. Maintenance spraying is neces- sary to prevent return of the brush.

Woody plants on right-of-ways restrict accessibility, constitute a fire hazard and may entangle transmission lines. Ground spray equipment has been used for most herbicide applications on right-of-ways in California.

Invert emulsions applied by helicopter with equipment already described have been used to a limited extent in Cali-

fornia. Since the swath width can be carefully regulated, practically all the spray falls on the right-of-way and plants immediately adjacent show little effect. However, a few fine droplets which may drift onto sensitive crops are produced, so caution is necessary.

Poison oak may be controlled by brush killer, amitrole, silvex, AMS, and pic- loram. Applications are most effective after all of the major stems have some mature leaves. Spraying should cease when the leaves start to turn red or yel- low. The most effective period for spray- ing will vary according to rainfall, eleva- tion, slope, etc., but seldom lasts over a month or two at any one location.

Complete control of poison oak re- quires one or more annual re-treatrnents. Occasional maintenance spraying should be planned after reasonable control has been achieved. Poison oak regrowth is slow in developing the \ ear following the initial spray, and treatment should be delaved until a few mature leaves have developed. Most efficient control is ob- tained by spraying every other year.

Brush killer is usually recommended for poison oak on rangeland because it is economical, and because it will at the same time control most other woody plants. Silvex is better than brush killer when applied at a very low volume with a mist blower.

[15

Picloram is also a good killer of poison oak but some re-treatment should be an- ticipated.

Amitrole is preferred for poison oak control around the home and in parks because it is less likely to damage wanted plants, and because it is effective over a longer period of the growing season than is brush killer. Amitrole will injure grass, however, and should be used with caution around conifers (see caution on use of amitrole on rangeland).

AMS may be used for controlling poison oak but is less effective than ami- trole.

Regulations on Injurious Herbicides

Certain herbicides including 2,4-D, 2,4,- 5-T, MCPA, 2,4-DP, and silvex are classi- fied as injurious materials because drift from treated areas may affect surround- ing desirable plants. Before they can be purchased or used, a permit must be ob- tained from the County Agricultural Com- missioner.

These phenoxy herbicides, particularly 2,4-D, 2,4,5-T, and silvex, are widely used for woody-plant control and are relatively nontoxic in amounts normally used. The precautions listed herein are for con- tinued safe use of herbicides rather than an indication of undue hazard.

Herbicide Residues

New herbicides and formulations are reg- istered and continually appear on the market. These herbicides will be included in the recommendations after the Uni- versity of California verifies their effective- ness and determines that the registered use will not result in a residue exceeding the legal tolerance when used under Cali- fornia conditions.

These suggestions for woody-plant con- trol are based on the best information currently available for each herbicide listed. If followed carefully, they should result in satisfactory control and should not leave residues that will exceed the tolerance established for any particular chemical. To avoid excessive residues, follow directions carefully with respect to dosage levels, number of applications, and minimum interval between applica- tion and harvest or grazing.

Drift of Herbicides

Drift of herbicides is by far the most important cause of illegal residues on forage crops and damage to susceptible crops. No herbicide can be applied by either aerial or ground equipment with- out some drift occurring; however, less drift occurs from a ground application than from an aerial application, and sprays cause less drift than do dusts.

Drift can be kept to a minimum and the contamination or damage to other crops reduced if certain precautions are observed in the selection of the herbicide, method of application, type of formula- tion (dust, spray, or granular), timing of treatment, wind direction and velocity and the distance between the point of application and the nearest susceptible crop downwind.

It is the responsibility of the farmer and the applicator to consider the above points before applying a herbicide. Where possible, these recommendations offer several alternatives for control. The herbi- cide which will best meet the require- ments for a safe application in respect to surrounding crops, animal farming oper- ations, beneficial insects and wildlife should be selected.

University of California Policy for Making Pest Control Recommendations

Pest control recommendations made by University of California personnel are based upon those materials for which there is specific information regarding effectiveness under California conditions, residues that will remain on the crop at harvest, phytotoxicity, and wherever pos- sible their effect upon beneficial preda- tors, parasites, honey bees, fish and other wildlife. Recommended chemicals must also be registered and labeled for use both by the United States Department of Agriculture and the California State De- partment of Agriculture.

Wildlife

To protect fish and other wildlife, do not apply known harmful herbicides over canals or streams and do not allow drain- age from treated fields to enter waterways immediately after application. Special

[16]

precautions regarding protection of wild- life species will be given, when necessary, in the recommendation.

THE GROWER IS RESPONSIBLE for residues on his own crop as well as for problems caused by drift from his property to other properties or crops.

ACKNOWLEDGMENTS

The authors wish to thank personnel of the Agricultural Extension Service, Cali- fornia Department of Agriculture, the State Division of Forestry, the Pacific Southwest Forest and Range Experiment Station of the U. S. Forst Service, and the Bureau of Land Management. Thanks

are also due to the commercial concerns and others with whom we have coop- erated and who have supplied information used in this bulletin.

In order that the information in our publications may be more intelligible it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical iden- tifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criti- cism implied of similar products which are not mentioned.

1 1

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Table 3. Control of Woody Plants Using the Cut-Surface Method (2,4-D Amine Unless Otherwise Indicated)*

Common	name of tree	Spacing of cuts	Comments
	Frillf	Late fall to late spring best
	Cuts 6 inches apart	Effective at all seasons.
Fir, Douglas	Cuts 6 inches apart	Some trees survive unless very carefully done
		Frill	Late fall through midsummer best
Madrone		Cuts 6 inches apart	Late fall through midsummer best
	FriUTuse 2,4,5-T, amine or silvex	Same chemical should be used on maple stumps
Oak, black		Frill	Late fall through midsummer best
Oak, interior live, yon live, tan an	California live, can- I California scrub	Frill	Late fall through spring best; these are vigorous sprouting species so careful application is necessary
Pine, digger and ponderosa	Cuts every 8 inches	Cuts must penetrate into the wood to be effective
Willow		Frill	Effective at all times

* See discussion of picloram, page 5. t Frill = continuous line of cuts.

Table 4- Control of Woody Plants with Basal Sprays*

Common name of plant	Chemical	Comments
	Brush killer	Spring is better than winter; make cuts in larger stems
Chamise, ceanothus, Scotch broom,		Sensitive and readily killed Make cuts in larger stems Thoroughly soak bases (crowns) for high degree of control March through early summer
Currants and gooseberries
Maple, bigleaf	2,4,5-T or silvex
	2,4,5-T
	Brush killer	Two fluid ounces per inch stem diameter; effective at all times
Oak, interior live, coast live, canyon	2,4,5-T best, but brush killer will do	Three fluid ounces per inch stem diameter; best in spring; make cuts in larger stems
		Spring and early summer; re-applications necessary Thoroughly wet all sides of the stems and crowns; best when soil has medium moisture content
Rose, California	2,4,5-T ester

* Use 16 lbs. actual chemical (ester formulations) per 100 gallons of diesel oil.

[24

APPENDIX

Common and scientific names of woody plants mentioned in tables 1, 2, 3, and 4.

Common name

Scientific name

Table under

which control

is outlined

Alder, red Alnus rubra 1,

Arrowweed Pluchea sericea 1

Blackberry Rubus spp 1

Blueblossom ceanothus Ceanothus thyrsiflorus .... 2

Buckeye, California Aesculus calif ornica 1,

Broom, Scotch Cytisus scoparius 1,

Broom, common Spartium junceum 4

Cascara, buckthorn Rhamnus purshiana 2

Ceanothus Ceanothus spp 1,

Ceanothus, bigpod C. megacarpus 2

Ceanothus, spiny C. spinosus 2

Ceanothus, wedgeleaf (buckbrush) . . C. cuneatus 2

Chamise (grease wood chamise) . . . Adenostoma fasciculatum .

Chaparral whitethorn Ceanothus leucodermis

Cherry Prunus spp

Chinkapin, Sierra evergreen .... Castanopsis sempervirens .

CofFeeberry, California Rhamnus California ....

Cottonwood Populus spp

Coyotebrush (kidneywort baccharis) . Baccharis pilularis ....

Currants and Gooseberries

Sierra gooseberry Ribes roezlii

Stink currant R. bracteosum

Sierra currant R. nevadense

Western black currant R. petiolare

Fuchsia gooseberry R speciosum

California gooseberry R. calif ornicum

Wax currant R. cereum

Lobbs gooseberry R. lobbii

Redflowered currant R. sanguineum

Sticky currant R. viscosissimum ....

Siskiyou gooseberry R. binominatum

Nutmeg currant R. glutinosum

Whitestem gooseberry R. inerme

Swamp black currant R. lacustre

Trailing black currant R. laxiflorum

Hupa gooseberry R. marshalii

Menzies gooseberry R. menziesii

Mountain gooseberry R. montigenum

Tulare gooseberry R. tularense

Deerbrush ceanothus Ceanothus integerrimus .

Deerweed (broom deervetch) .... Lotus scoparius

Elderberry Sambucus spp

Eucalyptus Eucalyptus spp

Fir, Douglas Pseudotsuga menziesii . . .

Golden fleece (Fleece Goldenweed) . Haplopappus arborescens .

Gorse Ulex europaeus

Grape Vitis spp

[25]

2, 3

2, 4

3, 4

Table under Common name Scientific name which control

is outlined

Hazel, California Corylus cornuta var 1

californica

Hollyleaf buckthorn Rhamnus crocea var. ... 1

ilicifolia

Laurel, California Umbellularia californica ... 3

Lupine, stream Lupinus rivularis 2

Madrone, Pacific Arbutus menziesii 1, 2, 3

Manzanita, nonsprouting Arctostaphylos viscida . . . . 1, 2

A. manzanita 1, 2

A. glauca 1, 2

Manzanita, sprouting A. patula 1

A. glandulosa 1

Maple bigleaf Acer macrophyllum 1, 3, 4

Maple, vine A. circinatum 1, 4

Mountain misery (or bear-mat) . . . Chamaebatia foliolosa .... 2

Mountain mahogany Cercocarpus spp 2

Nutmeg, California Torreya californica 2

Oak, blue Quercus douglasii 1, 2, 3, 4

Oak, California black Q. kelloggii 1, 3, 4

Oak, California scrub Q. dumosa 1, 2, 3

Oak, canyon live Q. chrysolepis 1, 3, 4

Oak, leather Q. durata 1

Oak, California live Q. agrifolia 1, 3, 4

Oak, interior live Q. wislizenii 1, 3, 4

Oak, Oregon white Q. garryana 1, 3

Oak, valley Q. lobata 1, 3

Oak, tan Litho carpus densijlor a . . . . 1, 2, 3, 4

Pine, digger Pinus sabiniana 3

Pine, ponderosa P. ponderosa 3

Poison oak (California poison oak) . . Rhus diver siloba 1, 2, 4

Rabbitbrush, green Chrysothamnus viscidiflorus . . 2

Redbud, California Cercis occidentalis 1

Redwood Sequoia semper vir ens .... 1

Rose, California Rosa californica 1, 4

Sage, creeping (Sonoma) Salvia sonomensis 2

Sage, purple (whiteleaf) S. leucophylla 2

Sage, white S. apiana 2

Sagebrush, big Artemisia tridentata .... 2

Sagebrush, low .A. arbuscula 2

Sagebrush, silver A. cana 2

Salmonberry Rubus spectabilis 1

Saltcedar Tamarix spp 1

Silktassel, Fremont Garrya fremontii 2

Snowbrush ceanothus Ceanothus velutinus .... 2

Sumac laurel Rhus laurina 2

Thimbleberry, western Rubus parviflorus 1

Toyon (Christmasberry) Photinia arbutifolia . . . . 1, 2

Tree of heaven (ailanthus) .... Ailanthus glandulosa .... 1

Tree tobacco Nicotiana glauca 4

Whitethorn, Mountain Ceanothus cordulatus .... 2

Willow Salix spp 1, 2, 3, 4

Yerba santa, California Eriodictyon calif ornicum ... 2

Yerba santa, woolly E. tomentosum 2

, 15m-5,'65(F1504)V.L.

ME!

A FARM 0

product r

Well, not exactly — you can't grow auto- mobiles on farms, but farm products are essential in manufacturing them. Consider the annual agricultural needs of just one major automobile company.

or, in terms of approximate acreage:

. 900,000 bushels of corn

736,000 bushels of flax- seed

74,000 bales of cotton

1 5,000 acres of corn

80,000 acres of flax 78,000 acres of cotton

During the same period this company used products derived from 364,000 sheep and 36,000 cattle — plus many other items such as hog bristles and beeswax. In all, produce equivalent to the output of 1,000 good-sized farms is needed yearly. No wonder a top executive in the automotive industry has said: "Our plants, here and throughout the world, would have to close their doors in a few days if their flow of agricultural materials were to stop."

Supplying America's countless industries — and feeding the nation bountifully — makes agriculture America's biggest and perhaps most important business. That is one reason why anything which affects agriculture affects everybody.