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Scouting Watch

August 17, 2005

Fall webworm is numerous on trees throughout Illinois. This is the second generation in the southern half of the state, the only generation in the northern half. Eggs are laid over an extended period, so be watchful for new colonies to show up over the next month. These are easily controlled by pruning out the caterpillar-containing webs or just stripping the webbing and caterpillars off the branch. If insecticides are used, be sure to use enough pressure to penetrate the webbing.

May beetles have been numerous in the Jacksonville area, feeding on tree leaves at night. With most May beetles emerging in May, these represent a genus, Phyllophaga, with many species. Different species emerge at different times of the year and may have shorter or longer life cycles than the typical 3-year May beetle life cycle. Southern Illinois usually has a Phyllophaga with a 1-year life cycle that emerges in late July and looks similar in size and color to masked chafers. Jacksonville is considerably farther north, and the beetle is dark reddish brown, about 3/4 inch long. Damage was occurring in early August. Carbaryl (Sevin) or other labeled insecticide should provide effective control.

Masked chafers are present in some areas of northeastern Illinois. For years, Jim Fizzell, former Extension adviser and active consultant, has reported masked chafer beetles emerging in the Park Ridge area in late July, which is a couple of weeks after the beetles typically die. Masked chafer adults are unable to feed and die within a week or two of emergence. These beetles have been positively identified as Cyclocephala, masked chafers. Although of scientific interest, the white grubs produced by these beetles will be killed if imidacloprid (Merit) or halofenozide (Mach 2) was applied earlier in the summer. However, if trichlorfon (Dylox) is applied in early August, it would likely be ineffective when these white grubs hatch in mid-August. This could explain live grubs a few weeks after a Dylox application.

Author: Phil Nixon


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