Southeastern U.S. Vegetable Crop Handbook - 2022 - 45

* Weed population. Weeds interfere with crop production in
many ways. They may compete for light, water, nutrients,
and space. The extent of this interference is dependant on
population and is usually expressed as weeds per foot of
row or weeds per square meter. Control measures are needed
when the weed population exceeds the maximum tolerable
population of that species.
Disease monitoring involves determining the growth stage
of the crop, observing disease symptoms on plants, and/or the
daily weather conditions in the field.
Disease control is often obtained by applying crop protectants
on a regular schedule. For many diseases, application
must begin at a certain growth stage and must be repeated every
7 to 10 days. When environmental conditions are favorable for
disease development, delaying a spray program will result in a
lack of control if the disease has progressed too far. For certain
diseases that do not spread rapidly, fields should be scouted regularly.
Predictive
systems are available for a few diseases. Temperature,
rainfall, relative humidity, and duration of leaf wetness
period are monitored, and the timing of fungicide application is
determined by predicting when disease development is most likely
to occur. One such program for Downy Mildew is available at:
http://cdm.ipmpipe.org/
Weather Conditions. These are important to consider before
applying a pesticide. Spray only when wind velocity is less than
10 miles per hour. Do not spray when sensitive plants are wilted
during the heat of the day. If possible, make applications when
ideal weather conditions prevail.
Certain pesticides, including biological insecticides (e.g.
BT's) and some herbicides, are ineffective in cool weather. Others
do not perform well or may cause crop injury when hot or
humid conditions are prevalent. Optimum results can frequently
be achieved when the air temperature is in the 70°F range during
application.
Strive for Adequate Coverage of Plants.
Improved control of aphids can be achieved by adding and
arrang ing nozzles so that the application is directed toward the
plants from the sides as well as from the tops (also see Alkaline
Water and Pesticides, which follows). In some cases, nozzles
should be arranged so that the application is directed beneath the
leaves. As the season progresses, plant size increases, as does the
need for increased spray gallonage to ensure adequate coverage.
Applying insecticide and fungicide sprays with sufficient
spray volume and pressure is important. Spray volumes should
increase as the crop's surface area increases. Sprays from highvolume-high-pressure
rigs (airblast) should be applied at rates
of 40 to 200 gallons per acre at 200 psi or greater. Sprays from
low-volume-low- pressure rigs (boom type) should be applied at
rates of 50 to 100 gallons per acre at 20 psi. The addition of a
spreader-sticker improves coverage and control when wettable
powders are applied to smooth-leaved plants, such as cole crops
and onions.
Use a dedicated sprayer for herbicides and a different sprayer
for fungicides and insecticides. Herbicide sprays should be
applied at between 15 and 50 gallons of spray solution per acre
using low pressure (20 to 40 psi). Never apply herbicides with a
high-pressure sprayer that was designed for insecticide or fungicide
application because excessive drift can result in damage
to nontarget plants in adjacent fields and areas. Do not add oil
concentrates, surfactants, spreader-stickers, or any other additive
unless specified on the label, or crop injury is likely.
Select the Proper Pesticide. Know the pests to be controlled
and choose the recommended pesticide and rate of application.
When in doubt, consult your local Extension office. The herbicide
choice should be based on weed species or cropping systems.
For
insects that are extremely difficult to control or are resistant,
it is essential to alternate labeled insecticides, especially
with different classes of insecticides. Be alert for a possible
aphid or mite buildup following the application of certain insecticides.
Caution:
Proper application of soil systemic insecticides is
extremely important. The insecticide should be placed according
to the label instructions (which, in general, indicate application
should be directed away from the seed) or crop injury may occur.
Be
sure to properly identify the disease(s). Many fungicides
control specific diseases but provide no control of others. For
this reason, on several crops, fungicide combinations are recommended.
Pesticide
Compatibility. To determine if two pesticides are
compatible, use the following " jar test " before you tank-mix pesticides
or tank-mix pesticides with liquid fertilizers:
1. Add 1 pint of water or fertilizer solution to a clean quart jar,
then add the pesticides to the water or fertilizer solution in the
same proportion as used in the field.
2. To a second clean quart jar, add 1 pint of water or fertilizer
solution. Then add 1/2 teaspoon of an adjuvant to keep the
mixture emulsified. Finally, add the pesticides to the water-adjuvant
or fertilizer adjuvant in the same proportion as used in
the field.
3. Close both jars tightly and mix thoroughly by inverting 10
times. Inspect the mixtures immediately and after standing
for 30 minutes. If a uniform mix cannot be made, the mixture
should not be used. If the mix in either jar remains uniform
for 30 minutes, the combination can be used. If the mixture
with adjuvant stays mixed and the mixture without adjuvant
does not, use the adjuvant in the spray tank. If either mixture
separates but readily remixes, constant agitation is required.
If nondispersible oil, sludge, or clumps of solids form, do not
use the mixture.
Note: For compatibility testing, the pesticide can be added directly
or premixed in water first. In actual tank-mixing for field
application, unless label direc tions specify otherwise, add pesticides
to the water in the tank in this order: first, wettable gran2022
Vegetable Crop Handbook for Southeastern United States
45
http://cdm.ipmpipe.org/
Southeastern U.S. Vegetable Crop Handbook - 2022

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