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June 23, 1999

Bagworms should be finished hatching and blowing from tree to tree by now, so this is the time to spray them with Bacillus thuringiensis kurstaki (Dipel, Thuricide) or pyrethroids. When checking a tree for infestation, use binoculars to check the top of the tree. Infestations are likely to be heaviest there.

The first generation of fall webworm is becoming obvious in extreme southern Illinois. Be alert for this insect throughout the southern half of the state. Control can be accomplished with forceful sprays into the webbing or simply by pruning off the webbing that contains the caterpillars.

Mimosa webworm is light this year, as one would expect following a cold winter. Even through southern Illinois and farther south through Kentucky, neither honey locust nor silk tree (mimosa) is showing much damage.

Cottony maple scale is numerous in some areas of northern Illinois and has become obvious with the production of the popcornlike egg sacs. This pest will be most numerous on silver maple, where it usually causes little damage aside from producing large amounts of honeydew that make cars and sidewalks sticky beneath the tree. When scouting this pest, look for whitish masses about 1/8 inch long that move when prodded. These masses are the larvae of the twice-stabbed lady beetle or a close relative. If these are numerous—that is, one for every 1 to 2 feet of infested branch—they will probably provide as much control to the scale as a crawler spray in mid-July. By mid-July, many of these larvae will have emerged as 1/8-inch-long, black lady beetles with two red spots on their backs. Be sure to double check for them before applying a crawler spray. A crawler spray will kill large numbers of the beetles and may set back eventual control of the pest. We primarily recommend a dormant oil spray to control this scale. During the winter, the adult lady beetles are under loose bark and protected from the spray.

Japanese beetle adults were first seen in Kentucky during the week of June 7, says Mike Potter, University of Kentucky Extension entomologist. Watch for them to show up in Illinois, although they have not appeared in central Illinois as of June 18. As mentioned last week, controlling early infestations may reduce feeding later.

Author: Phil Nixon


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