Euonymous caterpillars have been reported in large numbers in McHenry and DuPage counties. These whitish caterpillars with black spots can cover an entire bush with webbing and eat every leaf.
True white grub beetles are out in fairly large numbers throughout the state. These beetles are about one inch long and reddish brown. They are not annual white grub beetles, which are 1/2 inch long and tan. True white grub adults feed at night on the leaves of oak, crabapple, ash, and other trees. Carbaryl, sold as Sevin, is effective against these adults. Larval treatment on turf is should take place in late summer.
Eastern tent caterpillar continues to cause damage in scattered areas in the state; they have been noticed in large numbers in some areas of Lake, McHenry, Winnebago, Boone, and Ogle counties.
Honeylocust plant bug numbers appear to be light in most areas of central Illinois. Numbers are also low at The Morton Arboretum. However, a landscaper in Rockford reports large numbers.
Ash plant bug numbers are high enough to cause obvious stippling damage throughout the state. These numbers are usually not large enough to warrant treatment.
Flatheaded appletree borers should be treated at this time with chlorpyrifos (Dursban). This borer is particularly destructive to young maples and aging rose-family trees. On young maples it bores spirally up the trunk, starting near ground level, and feeds in the cambium just under the bark. On declining mountainash, serviceberry, hawthorn, and crabapple, it bores deep into the trunk. Emergence holes in all cases are D-shaped and slightly larger than 1/8 inch across.
Elm leaf beetle eggs should be hatching in southern and central Illinois. Sprays of carbaryl (Sevin) or any one of a variety of other insecticides should be effective against the young larvae.
Bagworm eggs should be hatching in central and southern Illinois. We recommend waiting on any spray applications for a couple of weeks when egg hatch should be done and the caterpillars quit blowing from tree to tree.
(Other contributors to this article: Staff at The Morton Arboretum; Jim Cavanaugh, Illinois Department of Agriculture)