Front Cover
 Table of Contents
 Back Cover

Group Title: Farmers bulletin
Title: Pasture brush weed control in the Virgin Islands
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00096185/00001
 Material Information
Title: Pasture brush weed control in the Virgin Islands
Series Title: Farmers bulletin
Physical Description: 8 p. : ill. (some col.) ; 28 cm.
Language: English
Creator: Adjei, Martin B
Davis, Olasee
University of the Virgin Islands
Donor: unknown ( endowment )
Publisher: Agricultural Experiment Station, University of the Virgin Islands
Place of Publication: Kingshill St. Croix
Kingshill St. Croix
Publication Date: 1999
Copyright Date: 1999
Subject: Brush -- Control -- Virgin Islands   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Spatial Coverage: United States Virgin Islands
Statement of Responsibility: by Martin B. Adjei and Olasee Davis.
General Note: Cover title.
General Note: "September 1999."
 Record Information
Bibliographic ID: UF00096185
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of the Virgin Islands
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 46953696


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Table of Contents
    Front Cover
        Front Cover
    Table of Contents
        Table of Contents
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
    Back Cover
        Page 9
Full Text
Farmers Bulletin No. 3
September 1999



Martin B. Adjei

Research Associate Professor (Agronomy)
Agricultural Experiment Station

Olasee Davis
Natural Resources Specialist
Cooperative Extension Service

University of the Virgin Islands

- w



Pasture brush weed control in the Virgin Islands

Pasture and grazing management .............

Traditional brush control methods ...........

Integrated mechanical and chemical brush weed control

Recommended foliar-applied herbicides

General precautions/restrictions on foliar-applied herbicides

Soil-applied herbicides

Safety precautions for the use of Spike ..

Herbicide application guidelines









Cover photos:
(1) Physic nut (Jatropha curcas)
(2) Casha (Acacia tortuosa & A. macracantha)
(3) Castorbean (Ricinus communis)
(4) Tan tan flower (Leucaena leucocephala)
(5) Maran (Croton astroites)
From Trees of Puerto Rico and The Virgin Islands, Second Volume, by Elbert Little, Jr., Roy Woodbury and Frank
H. Wadsworth, U.S. Department of Agriculture, Forest Service Agricultural Handbook No. 449, September, 1974.
1. (Cover and inside back cover) Acacia tortuosa (L.), p. 253.
2. Acacia macracantha, p. 245.
3. Psidium guajava L., p. 417.
4. Cordia alba (Jacq.), p. 841.
5. Croton astroites Dryand., p. 397.


Pastures make up approximately 80 percent or 15,000 acres of Virgin Islands farmland.
They are dominated by guineagrass (Panicum maximum) and leucaena (Leucaena
leucocephala) and provide the basic feed resource for the livestock industry. The mixture of
guineagrass and leucaena foliage provides excellent nutrition to livestock on the range if
properly managed. However, leucaena is an aggressive plant on Virgin Islands alkaline soils
and is capable of quick development into a woody brush unless it is mowed or shredded at
least once every year. It also tends to shed its leaves on the ground when cut and dried, leav-
ing only branches and stems, and, therefore, it is unsuitable in hay fields. Other less desirable
woody plants which may cause minor weed problems on pasture are manjack (Cordia alba),
maran (Croton astroites), guava (Psidium guajava), physic nut (Jatropha curcas) and castor-
bean (Ricinus communis).

Comparatively, casha (Acacia spp.) is the most noxious woody plant on Virgin Islands
pastures, infesting 90 percent of the fields and reducing available pasture by nearly 40 per-
cent. Both common types of casha (A. tortuosa and A. macracantha) are well adapted to the
semiarid climate and calcareous soils of the territory. Additionally, they are extremely tolerant
to fire, have high seed productive capacity and seed longevity. Moreover, their shrubby stems
and branches are covered with woody spines which protect even young plants from livestock
browsing. As the plants mature, the spiny horizontal branches combine to form impenetrable
bushy thickets that reduce forage production and hinder movement of livestock and light

Pasture and Grazing management

The major cause of widespread brush encroachment on pasture is improper grazing manage-
ment. Proper pasture management in the Virgin Islands should include
mowing of native pasture once yearly to remove unpalatable growth left
by the grazing animal, stimulate new grass growth and control the devel-
opment of shrubby weeds. Mowing not only prevents woody brush from
flowering and setting seed but also invigorates grass growth and competi-
tiveness. Good grazing management provides for
periods of rest to allow herbage to recover from graz-
ing. This normally requires dividing the pasture into
smaller units that are grazed in rotation (for example 3-7
days grazing followed by 28-35 days of rest). Many pastures
in the Virgin Islands are in advanced stages of deteriora-
tion because of improper management and overgrazing.
The optimum stocking rate (carrying capacity) for sus-
tainable livestock production in the Virgin Islands varies
from one adult cattle on 2 acres in the humid west to one
adult cattle on 5 acres in the dry east end of the island (eight
adult sheep are equivalent to one cattle unit). It is highly recommended
that farmers implement sound pasture and grazing management practices
before any expensive brush control measures are attempted.

Illustration: Casha, Acacia macracantha

Traditional Brush Control Measures

There are two casha roguing methods
commonly practiced in the Virgin Islands.
These are: (1) mechanical roguing (severing
and unearthing individual casha plants from
below the first lateral roots) and (2) applying
diesel oil to the basal growing points of indi-
vidual plants. Mechanical roguing uses hand
tools, tractors or bulldozers to cut and unearth
plants. Hand tools commonly used for casha
grubbing include the pick axe and mattock.

It is estimated that a bulldozer can remove
from three to seven casha plants per minute
depending on soil texture and moisture, plant
density and operator skill. A major
disadvantage of using tractors and bulldozers
for mechanical roguing is the removal of the
top soil and vegetation which adversely affects
the physical condition of rangeland and
promotes erosion. In addition, young plants are

Paul Flemming, AES Research Analyst, with

not perceived to represent a major problem in
pastures and are usually not removed in roguing
operations until they have matured to seeding
stage. Thus, mechanical roguing methods enhance
casha seed dispersal and germination while reducing
the vigor of desirable forages.

Application of diesel to the basal growing
points of individual plants is the other common
roguing practice. Diesel oil is a non-selec-
tive herbicide and must be applied care-
fully to avoid contacting adjacent for-
ages. Furthermore, basal application
of chemicals to individual casha
plants is cumbersome, expensive and
impractical over large areas. For these
reasons, and the possibility of long-term
Ssoil contamination, the use of diesel oil
for weed control is strongly discouraged.

Illustration: common guava, Psadlum guajava L.

S R- Integrated Mechanical and Chemical
wBrush Weed Control

Although various mechanical and cultural
control methods have been used for killing cash
plants in the Virgin Islands, the most efficient and
least disruptive to the environment is that which
integrates mechanical shredding with specific
translocated herbicides with little or no soil per-

The susceptibility of plants to herbicides is
controlled by:
(1) Stage of plant growth when treated
(2) Herbicide concentration absorbed by plant
(3) Inherent physiological and morphological
plant characteristics
(4) Inherent toxicity of the herbicide
(5) Environmental factors such as light, tempera-
ture, wind and, with soil-applied herbicide, soil

Generally, the stages of growth in which plants
Martin Adjel, AES Research Associate Profes- are most susceptible to applied herbicides are:
sor, with manjack. (1) when rapid growth is taking place and (2)
when a period of rapid growth has just ended and
food reserves are temporarily depleted or exhausted. Hence, as a rule, seedlings, young plants
and new regrowth are most susceptible. Dormant and non-germinating seeds and older plants are
not as adversely affected by herbicides.

Herbicides must gain entry into targeted plants and be translocated to susceptable sites in
concentrations great enough to induce the desired response. Obstacles to entry and move-
ment of foliar-applied herbicides in plants include waxy and hairy leaf cuticle, water stress,
heavy precipitation immediately following application external and internal make-up of the
plant such as leaf-angle, location of growing points and ability of the plant to inactivate or even
break down the chemical ingredient in the herbicide. Therefore, herbicides must be carefully
selected and applied in a proper and timely manner to control targeted plants.

Based on 5-year experimental results at the UVI-AES, it is strongly recommended that
chemical brush weed control on pastures in the Virgin Islands be preceded by mowing or
shredding 2-3 months before application. Ideally, pastures should be shredded after graz-
ing in February. The shrubs, because of their deep rooting system, will initiate regrowth during
the subsequent dry spell whereas grasses will remain relatively dormant. Selective herbicides
are then applied when brush is still in the lush, active stage of regrowth (2-3 months re-
growth or up to 3 feet high), but before they flower and/or set seed, in order to prevent a build-
up of seed reserves in the soil. Spraying herbicides on young regrowth also carries with it the
advantages of reduced chemical dosage necessary for control and reduced areal drift com-
pared with spraying tall trees.

The following herbicides have resulted in excellent woody brush control on pastures in the
Virgin Islands when applied under the right conditions and in the correct way: dicamba, piclo-
ram, triclopyr and tebuthiuron. They are described in detail below:


Dicamba (Banvel, Trimec Super Brush Killer)

Dicamba (3, 6-Dichloro-2-methoxy benzoic acid) be-
longs to the benzoic acid herbicide family. It is produced
by Sandoz Crop Protection Corp. Pure dicamba is
marketed as a liquid formulation of either the potas-
sium or dimethylamine salt under the trade name -
Banvel. It contains 4 pounds of active ingredient -
(ai) per gallon of product. Banvel bears the EPA
safety signal word "WARNING" and is nontoxic to
bees and fish.

Dicamba possesses plant regulatory proper-
ties similar to the phenoxy-carboxylic herbicides. It j
interferes with nucleic acid metabolism and dis-
rupts the transport system in plants due to in-
duced massive cellular proliferation. In addition to
its foliar activity, dicamba also persists in the soil
for a period of time resulting in control of germinating Illustration: white manjack, Cordia alba (Jacq.)
seedlings. The plant selectivity of dicamba is based on
the ability of tolerant plants like grasses to rapidly de-
grade it metabolically while broadleaf plants are unable
to degrade it quickly enough.
Several combinations of
dicamba with other herbicides
offer effective control of brush
weeds. They include Trimec
Classic (dicamba + 2,4-D +
MCPP); Trimec Brushmaster/
Brushkiller (dicamba + 2,4-D +
2,4-DP) and Mondak
(dicamba + MCPA).

Use 2 pounds active
ingredient of dicamba per
acre. Re-treatment of casha
with the same dosage is often
necessary within a year to
control incompletely-killed
Olasee Davis, CES Natural Resources Specialist, with cash. roots and crowns.

Picloram (Grazon, Tordon, Pathway, Access) '

Picloram (4-amino-3,5,6-trichloropicolinic acid) is
also a hormone-type herbicide used for the control of
woody broadleaf plants in rangeland and non-crop
areas. Most grass species are tolerant to picloram,
and selective control of broadleaf weeds with piclo-
ram in grass crops is feasible. It is rapidly absorbed
by foliage and roots of broadleaf plants, and it is
readily translocated throughout the plant via phloem
and xylem tissues-accumulating in regions of
active growth. It is usually formulated as a water-
soluble liquid with a blue-green color and alcoholic
odor. The more concentrated formulations of piclo-
ram such as Grazon PC, and Grazon P + D carry the
EPA safety signal word "WARNING." They are re-
stricted use pesticides (RUP) and do require a li-
censed applicator to dispense. Other formulations
such as Tordon (picloram + 2,4-D), Pathway
(triisopropanolamine salt of picloram + 2,4-D) and
Access (picloram +triclopyr) bear the EPA safety
signal word "CAUTION." Picloram related herbicides Tan tan on St. Croix.
are produced by DowElanco. Picloram has the ability
to seep or leach in sandy soil and must not be ap-
plied where the water table of an underlying aquifer is shallow. It is nontoxic to bees but
toxic to fish.

Use up to 1 pound acid equivalent per acre, annually, without any re-treatment.

Triclopyr (Remedy, Garlon 4, Grazon ET, Pathfinder, Crossbow, Confront)

Triclopyr (3,5,6-trichloro-2-pyridinyloxy acetic acid) is an amber-colored liquid which has
low volatility and photodegrades. Therefore, it must be kept away from light. It is produced by
DowElanco. Triclopyr is also hormonal in action, affecting broadleaf plants selectively. It de-
grades quite rapidly (half life = 20-40 days) in the soil from microbial activity.

Pure triclopyr-amine formulations such as Garlon 3A, Grandstand, Redeem and Turflon
carry the EPA safety signal word "DANGER" because they can cause skin and eye irrita-
tion and are toxic to fish. The tryclopyr-esters including Remedy, Garlon 4, Grazon ET and
Pathfinder are less toxic and bear a signal word "CAUTION." These may be used on pas-
tures in the Virgin Islands.
Triclopyr combination formulations recommended for brush control on pasture are
Crossbow (triclopyr + 2,4-D), Confront (triclopyr + clopyralid) and Access.

The maximum rate of triclopyr allowed during any year is 1 pound acid equivalent per acre.


The roots of plants are an important
Site of entry into the plants for soil-
applied herbicides. After application,
the first significant rain dissolves the
pellets or granules, moving the herbicide
into the soil. Additional rainfall takes her-
bicide into the root zone where it is ab-
sorbed by the roots of woody plants.

In the case of Spike (Tebuthiuron),
the herbicide is then translocated to
the stems and leaves where it
inhibits the leaves' ability to
produce food (photosynthesis).
Leaves turn yellow and die. Hence,

Illustration: Croton astroites Dryand.

General Precautions/Restrictions on Foliar-Applied Herbicides

(1) Herbicide should be applied in
sufficient volume of water (20-30 gallons
per acre) to ensure complete foliar

(2) Addition of a non-ionic surfactant at a
concentration of 16 fluid ounces per 100
gallons of water will promote herbicide
absorption by plants and enhance
(3) Do not spray under windy conditions
that will allow spray to drift to edible food
or feed crops, cropland or water which Olasee Davis operating boom sprayer.
will be used for irrigation or domestic
(4) With the exception of pure picloram, do not graze meat animals on or harvest forage
for hay within 30 days of treatment and withdraw meat animals from treated fields 7-30
days (depending on herbicide label) before slaughter.
(5) Do not graze lactating dairy animals on treated fields for 90-365 days following
(6) Be sure to read the herbicide label carefully before application. This is required by

most systemic, soil-applied herbicides work
slowly but surely, and may take 6-12 months
to complete woody brush kill.

Tebuthiuron, which is commonly marketed
under the trade name Spike 20P, is a very
effective soil-applied herbicide for the control of
both casha and leucaena along the fenceline.
Spike is also safe to use. Its heavy clay
pellets prevent lateral movement of herbicide
from target plants to sensitive crops or plants.

Once in the soil, spike is strongly adsorbed
onto clay soil particles from where it is picked
up by targeted plants or broken down by
microorganisms. Strong adsorption to soil
particles means minimum lateral movement
and leaching losses from the application site.
It degrades with time, and, because re-appli-
cation is infrequent (2-3 years), there is no
soil accumulation.

Being 80 percent inert clay, Spike 20P
PaulFlemmingwithmaran(Crotonastroltes). pellets are unattractive to animals and selec-
tive consumption by livestock is unlikely. If
inadvertently consumed by livestock, toxicity
is low: the herbicide is rapidly excreted and does not accumulate in animal tissue.

In all research studies, Spike has never been found deeper than 24 inches below
the surface of clay soil.

(4) Read and obey the full herbicide label as required by law.

Safety Precautions for the Use of Spike

(1) No surface application of Spike should be made to highly permeable soil such as
loamy sand to pure sand.

(2) No application is allowed where the water table of the underlying aquifer is shallow
(less than 5 ft) or within 200 ft of established dams or waterways.
(3) No surface application should be made on slopes greater than 10% in order to
prevent erosion losses. Injection into soil is the preferred method on steep slopes.






Method of



Trimec Super

Tordon RTU





Garlon 4

Spike 20P

Spike 20P

2 lb/acre(A)

2 Ib ai'/A

0.5 lb ae2/A

0.5 lb ae/A

0.25-0.5 lb ae/A

0.5 Ib ae/A

0.5 Ib ae/A

0.5 lb ae/A

4 grams/plant

7 grams/plant

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
2-3 months regrowth

Shred pasture & allow
3 month regrowth

Mature plant

Foliar broadcast

Foliar broadcast

Foliar broadcast

Foliar broadcast

Foliar broadcast

Foliar broadcast

Foliar broadcast

Foliar broadcast

Basal spot

Basal spot

6 months for first
year, then annually

6 months for first
year, then annually

1 year

1 year

1 year

1 year

1 year

1 year

2-3 years

2-3 years

active ingredient
2acid equivalent
Trade names have been used to simplify information; no endorsement is intended.













Use psides wit cr. Apl the onl to patorses lite on th
label. When miin an aplyn petcie folo all lae prcatin toS

protec yorsl and oter aroun you It Is a vilaio ofthawt

Copies of this bulletin available from:
Agricultural Experiment Station
University of the Virgin Islands
RR 2, Box 10,000, Kingshill, St. Croix 00850
(340) 692-4020

James E. Rakocy

Robin Sterns

This bulletin is issued jointly by the Agricultural Experiment Station and the Cooperative Extension Service
of the University of the Virgin Islands, and policies are consistent with federal and state laws and regulations on
nondiscrimination regarding race, color, national origin, religion, gender, age, disability and gender preference.

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