• TABLE OF CONTENTS
HIDE
 Front Cover
 Definitions
 Main














Group Title: Circular
Title: Chemical weed control in citrus groves
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00084392/00001
 Material Information
Title: Chemical weed control in citrus groves
Series Title: Circular
Physical Description: 19 p. : ill. ; 23 cm.
Language: English
Creator: Kretchman, Dale W
McCown, Jack T
University of Florida -- Agricultural Extension Service
Publisher: University of Florida, Agricultural Extension Service
Place of Publication: Gainesville Fla
Publication Date: 1962
 Subjects
Subject: Citrus fruits -- Weed control -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: D.W. Kretchman, J.T. McCown.
General Note: Cover title.
General Note: "April 1962."
 Record Information
Bibliographic ID: UF00084392
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 82606826

Table of Contents
    Front Cover
        Page 1
        Page 2
    Definitions
        Page 3
        Page 4
    Main
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
Full Text







Circular 224 April 1962
CHEMICAL WEED CONTROL
IN CITRUS GROVES
D. W. Kretchman J. T. McCown













DEFINITIONS


Herbicide-Any compound which will kill plants.

Non-selective herbicides-Those materials which kill most
types of plants.

Selective herbicides-Those materials which kill only certain
plant types or species.

Translocated herbicides-Those chemicals which are ab-
sorbed by one part of a plant and exert toxic effects on other
parts.

Growth regulating herbicides Chemicals which modify
growth processes of a plant in such a way as to cause death
of plants. They are often referred to as hormone weed killers.

Soil sterilants-Those materials which prevent the growth
of plants when present in the soil. The action may be temporary
or relatively permanent.
Pre-emergence treatment-Treatments made prior to weed
emergence.

Post-emergence treatment-Treatments made after weeds
have emerged.





The use of trade names in this publication is solely for the purpose of
providing specific information. It is not a guarantee or warranty of the
products named and does not signify that they are approved to the exclu-
sion of others of suitable composition.





COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director









CHEMICAL WEED CONTROL IN
CITRUS GROVES

D. W. KRETCHMAN* AND J. T. MCCOWNf

Weeds may cause problems in citrus groves. They compete
with citrus trees for moisture, nutrients, sunlight, and space.
They may be a source of insect and disease problems. Weeds
can prevent proper movement of water during periods of ex-
cessive rainfall or during irrigation operations. Weeds also
restrict movement of air during cold periods. They may impede
spraying and harvesting operations, and may constitute a se-
rious fire hazard. However, weeds do assist in the maintenance
of soil organic matter, in preventing soil erosion and tree damage
from both wind and water, and in preventing excessive loss of
soil nutrients during periods of extreme rainfall.
Weed control by cultivation is expensive and many times in-
adequate. Certain implements may cause serious root and trunk
damage as illustrated in Figure 1. Certain of the newer organic
herbicides offer effective weed control in citrus groves.
CAUTION: The recommendations in this bulletin are based
upon data obtained from three or
more years of field trials. The
residual or cumulative effects of
repeated applications of the
chemicals on citrus trees have
not been completely determined.
Therefore, growers are cautioned
not to use higher rates or more
frequent applications in groves
than those suggested. Improp-
er use of herbicides may result
in excessive amounts being ap-
plied. This may result in tree
damage and also illegal residues
within fruit. Read and follow ""
the label on the herbicide con- Figure 1.-Injury to trunk of
tainer. young citrus tree from improper
use of tree hoe.
Assistant Horticulturist, Florida Agricultural Experiment Stations.
t Assistant Citriculturist, Florida Agricultural Extension Service.
5





























Figure 2.-Mature citrus tree killed by excessive amounts of herbicides.

PRINCIPLES OF CHEMICAL WEED CONTROL
To obtain satisfactory weed control, the following principles
should be understood and applied.

Herbicides kill best when applied at the proper stage of
weed growth. Pre-emergence type herbicides are generally more
effective against weed seedlings than older plants. Growth reg-
ulator or hormone type chemicals are more effective when ap-
plied to young, vigorously growing weeds.

Soil moisture and rainfall affect herbicidal action. Poor
results with pre-emergence herbicides may occur when soil mois-
ture is too low to activate sufficient chemical to kill the weed
seedlings. However, heavy rainfall immediately after applica-
tion may leach the chemical out of the surface of the soil and
result in poor control. Foliage-absorbed chemicals may be
washed off of leaves by rainfall before adequate amounts can
be absorbed.

Proper rates should be used. Excessive rates may result
in injury to citrus trees and are more costly. Excessive amounts






of growth regulators may result in a poor kill because high dos-
ages may prevent proper translocation of the chemical to all
parts of the plant. Inadequate rates of herbicides may not pro-
vide satisfactory weed control.
Rates differ with soil type. Slightly higher rates are nec-
essary in the heavier soils of the coastal districts than in the
lighter soils of the interior section.
Citrus trees should be in good condition. Trees that have
been weakened by poor nutrition, insect, disease, frost, or trans-
planting damage will not tolerate as much chemical as healthy,
vigorous trees. Young trees are also more susceptible than older
trees.
The treated area should not be cultivated after application.
Disturbing the soil where pre-emergence herbicides have been
applied may destroy the chemical layer and may bring weed seeds
to the surface to germinate and grow. Cutting of weeds treated
with growth regulators may destroy their effects.
Prevent wind drift of the sprays or vapors. Do not apply
herbicides under windy conditions. High sprayer pressures
cause formation of small droplets which are easily carried by
wind currents. Only amine salts of 2,4-D or 2,4,5-T should be
used near citrus groves to prevent injury from vapor drift.

Figure 3.-Growth regulator type herbicide used to
control cattails in drainage ditch.


Ailkaji


%r'.-!.







Know your weed species. Certain chemicals are effective
only against certain species or types of weeds.
Know the chemical and its limitations. Read carefully the
label of any herbicide used. The label provides information on
chemical concentration, crops upon which it can be used, weeds
controlled, proper rates, suggestions for mixing and application,
special precautions, and other important considerations.

CHEMICALS
Dalapon.-Trade name: "Dowpon"; a leaf-absorbed, translo-
cated herbicide; selective against grasses; kills best when ap-
plied to young, vigorously growing grasses; should have at least
four hours drying time before rainfall; soluble in water but
not in oil and is somewhat corrosive to spray equipment; rela-
tively non-toxic to warm-blooded animals; has a temporary stunt-
ing effect on citrus trees from foliage or root absorption; should
not be used in groves under four years old.
Diuron.-Trade name: "Karmex"; a non-selective, root-ab-
sorbed, soil-sterilant type herbicide; a pre-emergence herbicide
at low rates; a wettable powder dispersable in water sprays, es-
sentially non-corrosive to spray equipment and non-toxic to
warm-blooded animals; soil moisture necessary for proper ac-
tion; may cause a yellow-veining of citrus foliage from root ab-
sorption; should not be used in groves less than one year old.
Fenuron.-Trade name: "Dybar"; or FenuronTCA.-Trade
name: "Urab"; non-selective, root-absorbed, soil-sterilant type
herbicides; very toxic to all plants; relatively non-toxic to warm-
blooded animals; soil moisture necessary for proper action;
should not be used near citrus trees or other desirable plants.
Methyl Bromide.-Trade name: "Dowfume MC-2"; a non-
selective soil fumigant; toxic to all plants and most seeds; a gas
under normal pressure and temperature; requires special appli-
cation methods and equipment; must be sealed in treated area
with air-tight covering; extremely toxic to warm-blooded ani-
mals; should not be used near citrus trees.
MonuronTCA.-Trade name: "Urox"; a non-selective, root-
absorbed, soil-sterilant type herbicide; toxic to most plants; rel-
atively non-toxic to warm-blooded animals; soil moisture neces-
sary for proper action; should not be used near citrus trees or
other desirable plants.
Silvex.-Trade name: "Kuron"; a leaf-absorbed, growth reg-















I hi I, Lr .0I I
I riury




L L I riI


r* .


Figure 4.-Top shows dalapon injury following improper use of the
herbicide. Lower picture shows toxicity symptoms on citrus leaves result-
ing from excessive applications of diuron.


I


*1

































Figure 5.-Proper use of herbicides results in good weed control.

ulator type herbicide, effective against fewer species of broad-
leaf plants than 2,4-D or 2,4,5-T; relatively non-corrosive to
spray equipment; essentially non-toxic to warm-blooded animals;
citrus trees can apparently tolerate up to 60 ppm without serious
damage but herbicidal concentrations should be kept off citrus
foliage and away from the tree root zone.
Simazine.-Trade name: "Simazine"; a non-selective, root-
absorbed, soil-sterilant type herbicide; a pre-emergence herbi-
cide at low rates; available as a wettable powder or granular
product; essentially non-corrosive to spray equipment and non-
toxic to warm-blooded animals; soil moisture necessary for prop-
er action; citrus trees show a very high tolerance to this chemi-
cal; should not be used in groves less than one year old.
2,4-D.-Available in several formulations and trade names;
a growth-regulator type herbicide; generally leaf absorbed; se-
lective against broadleaf weeds; relatively non-corrosive to spray
equipment; essentially non-toxic to warm-blooded animals; citrus







trees can apparently tolerate up to 40 ppm without serious in-
jury, but herbicidal concentrations should be kept off citrus fo-
liage and away from the tree root zone; the amine salt form
should be used to minimize the possibility of vapor drift.
2,4,5-T.-Available in several formulations and trade names;
similar in action to 2,4-D but generally kills more woody plant
species than 2,4-D; also relatively non-corrosive to spray equip-
ment and non-toxic to warm-blooded animals; tolerance of citrus
trees to low concentrations is not completely known, but herbi-
cidal rates should be kept off tree foliage and away from tree
root zone; only the amine salt form should be used near citrus
trees or other desirable plants.

EQUIPMENT
It is not necessary to buy expensive, high-gallonage, high-
pressure spray equipment for applying herbicides. Many pres-
ently available sprayers can be modified to apply herbicides. For
spraying under trees, a covered boom is desirable to prevent
spraying of the foliage, wind drift, or interference from tree
limbs. A commercial type of under-tree sprayer available is
illustrated in Figure 6.
A weed control sprayer should have the following features:
A pump with a minimum capacity of four gallons per min-
ute. It should be fairly resistant to abrasive action of wettable
powders and should be relatively inexpensive and easily replace-
able.
Preferably a metal or fiberglass tank which can be easily
and thoroughly cleaned.

Provisions for agitation, either mechanical or by using a
bypass from the pump. If the pump does not have enough ca-
pacity for bypass agitation, it can be provided by using a lower
tractor gear (increasing PTO speed) and by reducing the size
of orifice in the nozzle tips.
A spray boom which may be adjusted for height and with
nozzles which may be adjusted for distance between nozzles.
For spraying under trees, a cover for the boom is necessary.
The boom should be high enough and the nozzles so spaced to
allow a slight overlap of the spray pattern at the ground level
with pre-emergence herbicides or at the tops of the weeds when
applied post-emergence.







A pressure regulator and pressure gauge on or very near
the spray boom which accurately measures pressure up to 100
pounds per square inch.
Fifty-mesh screens in the intake line and in the nozzles.
Wettable powder formulations of simazine and diuron will not
readily pass through screens smaller than 50-mesh.
Flat-fan nozzles, illustrated in Figure 7, for boom spraying.
A nozzle size equivalent to TeeJet 8004 is adequate for most herb-
icide applications. A hand gun can be used for applying herbi-
cides to grove ditches provided pressure is low and droplet size
is large enough to minimize spray drift.
Granular applicators are available which will give relatively
uniform coverage but may be very difficult to calibrate. Granu-
lar applications to grove ditches can often be made by hand.

CALIBRATION

Since most herbicide recommendations are given as rate of
active ingredient per acre actually sprayed, it is extremely im-
portant to accurately calibrate spray equipment or granular ap-
plicators to determine the amount of material being applied per
acre. Most spray applications in groves can be made using 25
to 75 gallons per acre at a pressure of 20 to 50 pounds per square

Figure 6.-Sprayer mounted on tractor for applying herbicides
in citrus groves.


2







inch. Ditch spraying may require 200 to
300 gallons per acre for thorough cover-
age, but it is rarely necessary to use pres-
sures greater than 100 pounds.
A speedometer or tachometer is a de-
sirable feature on the tractor used for
spraying to provide accurate speed control
while spraying. This will also reduce the
number of calibrations necessary when one .
has several different locations to spray and
the tractor is stopped and started fre-
quently. /
The following steps give a good meth- /
od to calibrate a sprayer. .
1. Fill the sprayer with water only. Figure 7.-A flat-fan
2. Spray a measured area at a fixed type spray nozzle.
tractor speed and pressure setting under
conditions comparable to actual spray conditions.
3. Then measure the amount of water necessary to refill the
sprayer.
4. Multiply the number of gallons used in the measured area
by 43,560 (number of square feet in an acre) and divide the prod-
uct by the number of square feet in the measured area. This
will give gallons per acre.
5. Then add the correct amount of herbicide to the spray
tank to give the correct rate per acre.
As an example, if 10 gallons were used to spray an area 600
feet long and 10 feet wide, the volume of spray material applied
per acre would be 72.6 gallons. If you wish to apply simazine
at 6.4 pounds per acre and you have a 200 gallon tank, you would
add 22 pounds of Simazine 80W to the tank to obtain the desired
rate.
Calculations
10 x 43,560
= 72.6 gallons per acre
6,000
200
S= 2.75 acres to be sprayed per tank
72.6
2.75 x 6.4 = 17.6 pounds actual simazine needed per tank
17.6
= 22 pounds Simazine 80W needed per tank to give 6.4
.8 pounds per acre rate







WARNING: If you change the tractor speed, operating pres-
sure, nozzle size, or nozzle spacing, the amount of spray applied
per acre will change and re-calibration will be necessary.
Granular applicators are very difficult to calibrate and one
must revert to the trial and error method, using the actual herbi-
cide. By weighing out small quantities to be applied over small
areas, it is possible, with practice, to obtain rates of application
quite close to desired rates.
Uniform and thorough coverage is very important with all
herbicide applications but usually quite difficult to attain using
granular materials.

CLEANING APPLICATION EQUIPMENT
Herbicide application equipment should be thoroughly cleaned
immediately after use. Metal or fiberglass tank sprayers are
more easily cleaned than wooden tank sprayers. Most herbicides
can be satisfactorily removed from spray equipment if the
cleaning is properly done. Exceptions are 2,4-D and 2,4,5-T.
Equipment which has contained herbicidal concentrations* of
2,4-D or 2,4,5-T should not be used for applying insecticides and
fungicides.
It is important to clean all parts of a sprayer thoroughly in-
cluding pump, hoses, boom, and nozzles. When cleaning out
materials such as dalapon, diuron, and simazine, a thorough
rinsing with clean water is usually sufficient. However, with
growth regulators such as 2,4-D; 2,4,5-T, and silvex, a cleaning
agent should be used. The sprayer should first be thoroughly
rinsed with clean water and then partially filled with water.
Next add one gallon of household ammonia per 100 gallons of
water. The pump should be kept running long enough to allow
the cleaning solution to circulate through the entire system.
This solution should be left in the sprayer for at least two hours
and then sprayed out through the boom and nozzles. The sprayer
should then again be thoroughly rinsed with clean water.
Concentrations of 2,4-D recommended for prevention of fruit drop on
certain citrus varieties are not considered herbicidal.









SUGGESTIONS FOR CHEMICAL WEED CONTROL


RATES GIVEN ARE FOR POUNDS OF ACTIVE INGREDIENT PER ACRE ACTUALLY SPRAYED

Rate per Time of Weeds
Situation Chemical Acre Application Controlled Remarks


simazine


diuron


6.4 to 9.6 lbs.


3.2 to 4.8 lbs.


dalapon 3 applica-
tions of 1.5
to 3.0 lbs.
with 2- to
4-day
intervals


diuron


In spring to
weed-free area

In spring to
weed-free area

In spring very
soon after grass
starts to grow
or very soon
after grass
starts to regrow
following mow-
ing during other
times of year


3.2 to 4.8 lbs. In spring to
weed-free area


Annual Do not apply in groves under 1 year from plant-
weeds ing. Use higher rates in heavier soils of coastal
districts. Use only 1 application per year.

Annual Do not apply in groves under 1 year from plant-
weeds ing. Use higher rates in heavier soils of coastal
districts. Use only 1 application per year.


Perennial
grasses


Annual
weeds or
perennial
weed
seedlings


Do not apply in groves younger than 4 years.
Use higher rates only in heavier soils of coastal
districts. Use only 1 series of applications per
year. Use nonionic wetting agent in spray so-
lution. Do not apply to bare soil over tree root
zone.



Use higher rates in heavier soils of coastal dis-
tricts. May be used with the first application of
dalapon treatment above for control of para-
grass and guineagrass seedlings, but dalapon
application should be reduced from 3 to 2 appli-
cations. Use only 1 series of applications per
year.


Young non-
bearing
groves


Bearing
groves












Rate per
Acre

6.4 to 9.6 lbs.




2 applica-
tions of 3.7
to 5.6 lbs.
with a 5- to
10-day
interval


Time of
Application

In spring to
weed-free area



Any time when
grass is growing
vigorously


2,4-D 2 to 4 lbs. Any time when
and/or weeds are grow-
2,4,5-T ing vigorously


diuron 20 to 40 lbs. When ditches
are dry or con-
tain less than
2 inches of
standing water
monuron- 22 to 44 lbs. When ditches
TCA are dry or con-
tain less than
2 inches of
standing water


Weeds


Chemical

simazine




dalapon


Situation

Bearing
groves



Planting
sites and
non-crop
areas which
contain no
roots of
citrus trees


Grove
ditches
(bottoms
only)


Controlled Remarks

Annual Use higher rates in heavier soils of coastal dis-
weeds or tricts. Use only 1 application per year.
perennial
weed
seedlings
Perennial Repeated series of treatments necessary for com-
grasses plete elimination of grasses, especially those
(Not which produce viable seed. Plowing with mold-
torpedo- board turning plow 4 weeks after second appli-
grass) cation aids kill. Citrus may be planted 6 weeks
after second application. Use nonionic wetting
agent in spray solution.
Perennial May be included with first dalapon application
broadleaf above. Use amine salt form. See pages 8 and 9.
weeds,
vines and
brush
All weeds Most effective when applied to recently cleaned
ditches. Flush ditches well before using water
for irrigation or spraying.


All weeds Most effective when applied to recently cleaned
ditches. Flush ditches well before using water
for irrigation or spraying.






Rate per Time of Weeds
Situation Chemical Acre Application Controlled Remarks


2 applica-
tions of 3.7
to 5.6 lbs.
with a 5- to
10-day
interval


Any time weeds
are growing
vigorously


2 to 4 lbs. Any time weeds
are growing
vigorously


4 lbs. Any time weeds
are growing
vigorously


simazine 1.6 lbs. twice
a year if
needed or
3.2 lbs. once


diuron 1.6 to 3.2 lbs.


To weed-free
area in spring
(3.2 lb. rate) or
in spring and
summer (1.6
lb. rate)

In spring to
weed-free area


Grove
ditches
(general)


dalapon


20 to 40 lbs. Any time


All weeds Do not use in areas where chemical may be
leached into rooting zones of citrus or other de-
sirable plants. May last 2 years or more.


Perennial
grasses
and
cattails


Broadleaf
weeds,
vines, and
brush

Broadleaf
weeds,
vines, and
brush

Annual
weeds




Annual
weeds


Keep spray drift off citrus foliage and away from
tree rooting zone. Use nonionic wetting agent
in spray solution.



Use amine salt forms. Keep spray drift off citrus
foliage and away from tree rooting zone. If
brush is tall, cut off and treat sprouting stumps.
May be used with first application of dalapon.

Keep spray drift off of citrus foliage and away
from tree rooting zone. Not as effective against
certain brush species as 2,4,5-T.

Use on a limited trial area only. Band treat
along row. Do not disturb soil after treatment.
Use higher rate in heavier soils of coastal dis-
tricts.


Use on a limited trial area only. Band treat
along row. Do not disturb soil after treatment.
Use higher rate in heavier soils of coastal dis-
tricts. May cause yellow veining of leaves at
excessive rates.


2,4-D
and/or
2,4,5-T

silvex


Citrus
nurseries
(EXPERI-
MENTAL
TRIALS)


Weed
encroach-
ment
barriers


diuron













Rate per Time of Weeds
Situation Chemical Acre Application Controlled Remarks


Weed
encroach-
ment
barriers


Burrowing
nematode
Suffer zones
oo


fenuron



fenuron-
TCA


diuron


50 lbs.



100 lbs.


Any time



Any time


20 to 40 lbs. After fumiga-
tion and area
has been leveled


monuron- 33 to 44 lbs. After fumiga-
TCA tion and area
has been leveled


Spot eradi-
cation of
torpedo-
grass


methyl
bromide


1% to 4 lbs.
per 100
sq. ft.


Any time to
well-tilled soil


Torpedo- Do not use in areas where chemical may be
grass leached into rooting zones of citrus or other de-
sirable plants. May last up to 1 year.

Torpedo- Do not use in areas where chemical may be
grass leached into rooting zones of citrus or other de-
sirable plants. May last up to 1 year.
All weeds Use higher rates if perennial grasses are present.
Do not treat outside of fumigated area. May last
2 years or more. Light discing at 6-month in-
tervals may increase length of control.

All weeds Use higher rates if perennial grasses are present.
Do not treat outside of fumigated area. May
last up to 2 years. Light discing at 6-month in-
tervals may increase length of control.

Torpedo- If citrus trees present, remove carefully before
grass treatment. Keep gas sealed in area 48 hours or
more. Replanting of trees may be done 7 to 10
days after treatment.


READ AND HEED THE LABEL ON THE CONTAINER









CONVERSION TABLE

The table converts rate per acre of active ingredient to rate
of commercial product for several herbicides and rates given in
this bulletin. Equivalent rates of commercial products other
than those presented can be calculated by dividing the rate per
acre of active ingredient desired by the percent active ingredient
per pound in the commercial product and multiplying the answer
by 100.

Equivalent
Rate per
Chemical Commercial Usual Percent Rate per Acre of
Product Active Acre Active Commercial
Ingredient Ingredient Product


dalapon


diuron


fenuron
fenuronTCA
monuronTCA
silvex
simazine




2,4-D
2,4,5-T


Dowpon


Karmex


Dybar
Urab
Urox
Kuron
Simazine 80W


Simazine 4G

(Many available)
(Many available)


25%
22%
22%


1.5
3.7
5.6
3.2
4.8
40.0
50.0
100.0


44.0 lbs. 200.0 lbs.


4 lbs./gal. 4.0 lbs.
80% 1.6 Ibs.
6.4 lbs.
8.0 lbs.
4% 1.6 lbs.
6.4 lbs.
4 lbs./gal. 2.0 lbs.
4 lbs./gal. 2.0 Ibs.


2.0
5.0
7.5
4.0
6.0
50.0
200.0
455.0


1.0 gal.
2.0 lbs.
8.0 lbs.
10.0 lbs.
40.0 lbs.
160.0 lbs.
0.5 gal.
0.5 gal.




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs