Page 17 - 01 Cotton SA May 2013

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A regular scouting program may prevent big losses incurred by pests.
<< p16 Insect populations often are concentrated in certain areas Biological coNtrol
of a field. Insects are normally not distributed uniformly in the field Predators (ants, ladybeetles, spider, etc.) and parasites (wasps) are
and do not infest all fields in an area. Large areas of the field must the dominant biological control agents of the cotton pests but their
be covered each time. Scouting aids in determining the kinds of dependability and efficiency generally are much lower than that of
insects present, their location, relative abundance and distribution in the chemical control. Biological control organisms, along with other
the field and numbers of insects or amount of insect damage to the factors such as climatic conditions often maintain cotton pests below
plants. Scouting only near turn rows and field margins is inadequate numbers that cause economic crop losses. To establish predator
for determining insect infestation. To cover the field completely, walk densities at which no action is needed is crucial to maintain pests
a field in a “zigzag” pattern crossing it diagonally from one corner to below the economic threshold. It is essential to know which predators
another or walk it in-a wide arc taking samples from several plants.
The pattern followed should allow adequate sampling throughout are most abundant and efficient and when they move to or from
the field, including the centre, the sides and corners. Sampling the field. Knowledge of predator effectiveness against individual
pest species also is needed. The time of peak predator densities and
pattern should be determined by the shape and size of the field. Avoid
sampling in the same area of the field on successive sampling days. average densities varies from one area to another depending on prey
The numbers and kinds of insects in a field usually are determined availability, growth stage of the cotton plant, predator distributions
with reasonable reliability by examining squares and leaves from and many other factors.
the terminal or entire plant or by sweeping the top part of a plant. The species and number may vary in some years and in some places.
Samples also may include any insects in the flowers, the rate at which In general, small predators feed on small prey such as eggs and small
squares are being set. Determine any “natural” excessive square or boll larvae, and larger predators kill large worms. Thus, identification of
shed when making an evaluation. Remember to consider the effect small, immature insect and predators, as well as adults, is important in
the weather has on the crop when evaluating fruit loss. pest management. A complex of predator species can coexist and bring
stability to the system. As any one pest species increases, bringing it
treatmeNt tiPS out of balance with the system, predators switch to this new food
It is crucial to scout regularly to determine insect population levels source and again bring the pest into equilibrium. Natural enemies are
and to time insecticide applications. Where control problems occur, of great economic benefit to the cotton farmer. They voluntarily enter
first check your sprayer calibration and insecticide rates to ensure the cotton field, are self-multiplying and are completely free of cost.
they are correct. Be especially suspicious of high percentages of insect Natural enemies are important in regulating pest insects but are not
pests surviving multiple applications of insecticides. It is essential to numerous enough to control excessive numbers that occur during
also guard against suspected resistance problems in the field. major outbreaks. Along with other mortality agents, natural >> p19

Katoen sa Cotton 17 Jan - Mei/May 2013