Southeastern U.S. Vegetable Crop Handbook - 2022 - 46

ules or powders, then flowables, emulsifiable concentrates, water
solubles, and companion surfactants. If tank-mixed adjuvants are
used, these should be added first to the fluid carrier in the tank.
Thoroughly mix each product before adding the next product.
Select Correct Sprayer Tips. The choice of a sprayer tip for
use with many pesticides is important. Flat fan-spray tips are
designed for preemergence and postemergence application of
herbicides. These nozzles produce a tapered-edge spray pattern
that overlaps for uniform coverage when properly mounted on a
boom. Standard flat fan-spray tips are designed to operate at low
pressures (20-40 psi) to produce small-to medium -sized droplets
that do not have excessive drift. Flat fan-nozzle tips are available
in brass, plastic, ceramic, stainless steel, and hardened stainless
steel. Brass nozzles are inexpensive and are satisfactory for
spraying liquid pesticide formulations. Brass nozzles are least
durable, and hardened stainless steel nozzles are most durable
and are recommended for wettable powder formulations, which
are more abrasive than liquid formulations. When using any
wettable powder, it is essential to calibrate the sprayer frequently
because, as a nozzle wears, the volume of spray material delivered
through the nozzle increases.
Flood-type nozzle tips are generally used for complete fertilizers,
liquid N, etc., and sometimes for spraying herbicides
onto the soil surface prior to incorporation. They are less suitable
for spraying postemergence herbicides or for applying fungicides
or insecticides to plant foliage. Coverage of the target is
often less uniform and complete when flood-type nozzles are
used, compared with the coverage obtained with other types of
nozzles. Results with postemergence herbicides applied with
flood-type nozzles may be satisfactory if certain steps are taken
to improve target coverage. Space flood-type nozzles a maximum
of 20 inches apart, rather than the suggested 40-inch spacing.
This will result in an overlapping spray pattern. Spray at the
maximum pressure recom mended for the nozzle. These techniques
will improve target coverage with flood-type nozzles and
result in more satisfactory weed control.
Full and hollow-cone nozzles deliver circular spray patterns
and are used for application of insecticides and fungicides to
crops where thorough coverage of the leaf surfaces is extremely
important and where spray drift will not cause a problem. They
are used when higher water volumes and spray pressures are recommended.
With cone nozzles, the disk size and the number of
holes in the whirl plate affect the output rate. Various combinations
of disks and whirl plates can be used to achieve the desired
spray coverage.
Alkaline Water and Pesticides. At times applicators have commented
that a particular pesticide has given unsatisfac tory results.
Usually, these results can be attributed to poor application,
a bad batch of chemical, pest resis tance, weather con ditions, etc.
However, another possible reason for unsatisfactory results from
a pesticide may be the pH of the mixing water.
Some materials carry a label cautioning the user against
mixing the pesticide with alkaline materials. The reason for this
caution is that some materials (in par ticular the organophosphate
insecticides) undergo a chemical reaction know as " alkaline hydrolysis. "
This reaction occurs when the pesticide is mixed with
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alkaline water; that is, water with a pH greater than 7. The more
alkaline the water, the greater the breakdown (i.e., " hydrolysis " ).
In addition to lime sulfur, several other materials provide alkaline
conditions: caustic soda, caustic potash, soda ash, magnesia
or dolomitic limestone, and liquid ammonia. Water sources in
agricultural areas can vary in pH from less than 3 to greater than
10.
To check the pH of your water, purchase a pH meter or in
most states you can submit a water sample to your state's soil or
water testing lab. If you have a problem with alkaline pH, there
are several products available that are called nutrient buffers that
will lower the pH of your water.
There are some instances when materials should not be
acidified, namely, sprays containing fixed copper fungicides, including:
Bordeaux mixture, copper oxide, basic copper sulfate,
copper hydroxide, etc.
BENEFICIAL INSECTS
A number of environmental factors, such as weather, food availability,
and natural enemies combine to keep insect populations
under control naturally. In some human-altered landscapes, such
as in agricultural crop fields, the levels of natural control are
often not acceptable to us, and we have to intervene in order
to lower pest populations. While some environmental factors,
such as weather, cannot be altered to enhance control of pests,
others such as populations of natural enemies, can be effected.
The practice of taking advantage of and manipulating natural
enemies in order to suppress pest populations is called biological
control.
Approaches To Biological Control. There are three general approaches
to biological control: importation, augmentation, and
conservation of natural enemies. Each of these techniques can be
used either alone or in combination in a biological control program.
Importation:
Importation of natural enemies, sometimes referred
to as classical biological control, is used when a pest of exotic
origin is the target of the biocontrol program. Pests are constantly
being imported into countries where they are not native, either
accidentally, or in some cases, intentionally. Many of these introductions
do not result in establishment or if they do, the organism
may not become a pest. However, it is possible for some
of these introduced organisms to become pests due to a lack of
natural enemies to suppress their populations. In these cases, importation
of natural enemies can be highly effective.
Once the country of origin of the pest is determined, exploration
in the native region can be conducted to search for
promising natural enemies. If such enemies are identified, they
may be evaluated for potential impact on the pest organism in
the native country or alternatively imported into the new country
for further study. Natural enemies are imported into the U.S. only
under permit from the U.S. Department of Agriculture. They
must first be placed in quarantine for one or more generations
to be sure that no undesirable species are accidentally imported
(diseases, hyperparasitoids, etc.). Additional permits are required
for interstate shipment and field release.
2022 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2022

Table of Contents for the Digital Edition of Southeastern U.S. Vegetable Crop Handbook - 2022
