Insect Management
Cotton Insect Management
Spider Mites -
Tetranychus Species
Description
Several species of mites occur on cotton, but one of the most common is the
two-spotted spider mite. Mites are not true insects but are related to spiders.
The adult spider mite is very small and about 1/60 to 1/80 of an inch in length.
The adult has four pair of legs (insects have three pair). It appears to have
two spots on its back, thus the name two-spotted spider mite. Their color ranges
from green or orange to straw colored. The adults and nymphs may be seen by
looking on the underside of leaves with a hand lens.
Biology
The two-spotted spider mite has a very short life cycle, completed from egg
to adult in five to seven days during the summer. Spider mites pass through the
developmental stages of egg, larva (three pairs of legs), nymph, and adult.
Mites feed on cotton and a wide range of other plants including apple, peach,
strawberries, corn, soybean, various weeds, ornamentals, and others. Two-spotted
spider mites have several natural control agents such as predaceous mites,
minute pirate bugs, predaceous thrips, and diseases that control mite
populations. Spider mites feed and reproduce on the underside of leaves. Initial
infestation occurs along leaf midribs.
Damage
Spider mite infestation causes very small yellow spots to appear on the
leaves resulting in a speckled appearance. The leaves may turn a red color
during dry weather or when the infestation becomes heavier. Areas in fields
infested with spider mites may appear lighter in color or reddish from a
distance.
Scouting
Spider mite infestation is determined by direct examination of suspected
areas while walking fields. Population levels should be classified according to
the following criteria.
None - No spider mites present.
Light - Spider mites found on an occasional plant - 1 to 10 per
leaf. Some speckling of
the leaves.
Medium - Spider mites are present on numerous plants - 11 to 25 per
leaf. The leaves
are speckled and mottled yellow or red.
Heavy - Spider mites are numerous on most plants - greater than 26
per leaf. Leaves are
reddish-brown in color.
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