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May 11, 2005

Gypsy moth larvae are feeding in northeastern Illinois. As of April 30, the larvae were up to 3/8 inch long and had already caused considerable feeding damage on emerging oak leaves. On trees with high populations, where egg masses were numerous and easily seen on the tree trunks and scaffold limbs, gypsy moths were feeding on leaves on the lower, as well as upper, leaves on the tree. Egg masses were still hatching on the east and north sides of trees and in bark crevices where reduced sunlight resulted in cooler conditions. The newly hatched larvae were still sitting on the egg masses in those areas. Leaves are rapidly expanding, so sufficient leaf area will soon be present to make spray applications effective.

Eastern tent caterpillar continues to be numerous in the southern half of Illinois. In the Springfield area, tents are easily seen, with caterpillars being about half grown. Application of Bacillus thuringiensis ‘kurstaki’ (Dipel, Thuricide) or other labeled insecticides should still provide effective control. In many areas of southern Illinois, the caterpillars will be too large for insecticide applications to save much leaf damage. Because eastern tent caterpillar eggs hatch over a couple of weeks, there may be individual trees where the caterpillars are still only about 1 to 1-1/4 inch long. In these situations, control will still prevent a considerable amount of defoliation from occurring.

Boxwood psyllids are also hatching, particularly in the northern half of the state. Early damage will show as the leaves being cupped at the ends of the branches. Later, these leaves will turn yellow and then brown as feeding continues. Application of acephate (Orthene) at this time should be effective.

Euonymus caterpillar is a whitish caterpillar covered with black spots that is appearing in silk webs on spindle tree, Euonymus europa. They can be controlled with a forceful spray into the silk webbing of Bacillus thuringiensis ‘kurstaki’ (Dipel, Thuricide) or other labeled insecticide.

Succulent oak gall is numerous on pin oaks in central Illinois. These look similar to gooseberries or green marbles that turn reddish on the twigs. The gall wasps cause the tree to use leaf tissue to form these galls and commonly part of the leaf or leaf tip extends from the gall. There is no control of these insects at this time. The galls will soon shrivel, turn black, and be covered by subsequent leaf emergence.

Author: Phil Nixon Morton Arboretum


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