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Division of Agricultural Scie

n c e s

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.

[2]

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.

[3]

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

[4]

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

[5]

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,

[6]

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

[7]

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.

[8]

2. Live oak regrowth controlled with fenuron pellets.

APPLICATION EQUIPMENT

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.

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.

[10]

, ■

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

untreated plots on left

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.

[in

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.

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