Southeastern U.S. Vegetable Crop Handbook - 2023 - 31

Second, determine if natural enemy releases are appropriate
for your specific situation. Sometimes knowledge of crop and
cultural practices that encourage naturally-occurring biological
control agents can allow you to maximize the control they provide.
By conserving these natural enemies, pesticide use (and
therefore expense) can be minimized.
Usually, released natural enemies work best as a preventative
pest management method. That is, if they are introduced
into your crop at the beginning of a pest infestation, they can
prevent that population from developing to damaging levels. If
you wait until pests have become a problem before releasing natural
enemies, the use of natural enemies usually will not work.
Therefore, pest problems must be anticipated and planned for
by carefully monitoring pest population development. Effective
trapping, monitoring, and field scouting should be used to determine
when pests appear, and to determine the timing of natural
enemy releases.
If you decide to use commercially available biological
control agents, you should choose your product and supplier
carefully. Once you have received your natural enemies, handle
them with care, following all instructions provided by your
supplier. The number or rate of natural enemies to release can
be determined through consultation with a reliable supplier, as
can the timing of application. Because natural enemies are living
organisms, adverse conditions (e.g. stormy weather, pesticide
residues) can kill them or reduce their effectiveness. Because the
actions of natural enemies are not as obvious as those of pesticides,
it may be important to work with your supplier to develop
a procedure to evaluate the effectiveness of your releases.
Further details of the above suggestions are provided in
Table 13. Remember, just because an organism is sold as a " natural "
or " biological " control does not mean it will work as you
expect. For example, praying mantids are general " ambush "
predators that will eat anything small enough (usually mobile insects)
that pass in front of them. They do not specifically attack
pests that growers are usually interested in removing. Another
example is ladybeetle adults that have been " pre-conditioned. "
These ladybeetles will just as readily leave the area that you
have treated as ladybeetles that have been collected and not
pre-conditioned.
This does not mean that biological control will not work for
your situation. There are a number of products and approaches
that can provide very satisfactory results.
Finally, if insecticides are necessary to control a pest,
choose a product that is least harmful to the beneficial(s) you
are trying to preserve. Listed in Table 13A is the relative safety
of different pesticides to key groups of beneficial organisms in
most important in vegetable systems.
For the most current information about suppliers of organisms
and related products, the purchase of natural enemies, and
how to effectively use them, consult with Extension.
DIAGNOSING VEGETABLE CROP
PROBLEMS
When visiting a vegetable field, follow the steps outlined below to
help solve any potential problems. All vegetable problems, such as
poor growth, leaf blemishes, wilts, rots, and other problems should be
promptly diagnosed. This is necessary for the grower to implement
prompt and effective corrective measures or to help reduce the probability
of its reoccurrence in following crops or its spread to susceptible
neighboring crops.
1. Describe the problem.
2. Determine whether there is a pattern of symptomatic plants in
the field.
a. Does the pattern correlate with a certain area in the field,
such as a low spot, poor-drainage area, or sheltered area?
b. Does the pattern correlate with concurrent field operations,
such as certain rows, time of planting, method of
fertilization, or rate of fertilization?
3. Try to trace the history of the problem.
a. On what date were the symptoms first noticed?
b. Which fertilizer and liming practices were used?
c. Which pest-management practices were used to manage
diseases, undesirable insects, and weeds - which chemicals
(if any), were applied, at what application rates, and
what was the previous use of equipment that was used for
application?
d. What were the temperatures, soil moisture conditions,
and level of sunlight?
e. What was the source of seed or planting stock?
f. Which crops were grown in the same area during the past
3 or 4 years?
4. Examine affected plants to determine whether the problem is
related to insects, diseases, or cultural practices.
a. Do the symptoms point to insect problems? Insect problems
are usually restricted to the crop. (A hand lens is
usually essential to determine this.)
(1) Look for the presence of insects, webbing, and frass
on foliage, stems, and roots.
(2) Look for feeding signs such as chewing, sucking, or
boring injuries.
b. Do the symptoms suggest disease problems? These
symptoms are usually not uniform; rather, they are specific
for certain crops.
(1) Look for necrotic (dead) areas on the roots, stems,
leaves, flowers, and fruit.
(2) Look for discoloration of the vascular tissue (plant
veins).
(3) Look for fungal growth.
(4) Look for virus patterns; often these are similar to
injury from 2,4-D or other hormones and nutritional
problems.
(5) Examine roots for twisting or galling.
2023 Vegetable Crop Handbook for Southeastern United States
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Southeastern U.S. Vegetable Crop Handbook - 2023

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