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Scouting Watch

August 31, 2005

Fall webworm continues to be numerous throughout the state. Bacillus thuringiensis kurstaki (Dipel, Thuricide) or other labeled insecticides are effective if the insecticide gets inside the silk tent. Pulling off the silk tent and associated caterpillars or pruning off the tents is also effective. This late in the season, most active infestations have completed the damage they are going to cause, so ignoring them is also an option. Stripped branches will produce leaves next year.

Yellownecked caterpillar is common throughout southern Illinois. Thanks to Kevin Black for his report from Rend Lake. This colonial caterpillar does not build a silk tent. It has several longitudinal bold whitish to yellowish stripes on the body. The body is red when the caterpillars are young, black when older. It feeds on crabapple, maple, oak, pecan, hickory, walnut, and many other trees. Its close relative, the walnut caterpillar, feeds only on walnut and hickory, including pecan. Walnut caterpillar is also red when young, black when older. It has only a few thin white stripes; older caterpillars have scattered, long, white hairs. Control options are the same as for fall webworm, except there is no silk tent to contend with.

Lacebugs are common on sycamore and cotoneaster. Adults are flat-topped, 1/8-inch-long bugs with white, lacelike wings. Their nymphs are dark brown to black, diamond-shaped, smaller insects. Both the nymphs and adults live on the leaf underside, being concentrated along the major veins. They feed by sucking out the leaf sap, causing whitish stippling on the leaf upperside. The undersides of infested leaves are frequently covered with the tiny black spots of their tarlike feces. Control is rarely needed on these insects, although sprays of acephate (Orthene), carbaryl (Sevin), cyfluthrin (Tempo), and insecticidal soap are effective.

Author: Phil Nixon


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