Southeastern U.S. Vegetable Crop Handbook - 2021 - 44

mite pests. In some cases, the chemical and physical defenses that
plants use to protect themselves from pests may reduce the effectiveness
of biological control.
An example of how conservation can work involves the diamondback
moth, Plutella xylostella (L.). This insect has developed
into the most important pest of crucifers in recent years due to the
pest's development of resistance to most pesticides. Two parasitoids,
the Ichneumonid wasp Diadegma insulare (Cresson) and the
braconid wasp Cotesia plutellae (Kurdjunov), can help reduce diamondback
moth populations if excessive pesticide applications are
avoided, especially with reductions in the use of pyrethroids. BT
products can work well to suit this purpose. Therefore, by simply
being selective in the type of pesticide used, and by spraying only
when threshold levels are reached, free control can be provided by
natural enemies already present in the field.
Incorporating Biological Control Into A Pest Management
Program: Biological control can be an effective, environmentally
sound method of managing pests. However, when trying to make
the best use of natural enemies in your crop, it may be helpful to
consider the following suggestions.
First, make sure you have your pest(s) accurately identified. Extension
can help with this. Consulting your local Extension office is
a good practice regardless of which pest control method you use.
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 ladybee44
tle
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.
2021 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2021

Table of Contents for the Digital Edition of Southeastern U.S. Vegetable Crop Handbook - 2021
