Issue 13, July 31, 2009

Scouting Watch

Japanese beetle adult numbers continue to be heavy in southern Illinois but less so in the northern two-thirds of the state, with some exceptions. Historically, winter survival of numerous insects tends to be higher in the expanded Illinois River Valley area in western Illinois. Correspondingly, high numbers of Japanese beetles are being seen in the Peoria and Monmouth areas. High numbers have also been reported from the Rockford area.

White grub numbers are still unknown, although they should have hatched in southern Illinois. Scouting in the Urbana area on July 30 did not reveal any grubs yet. We expect hatching in central Illinois to occur during the first week of August and should occur towards the end of that week in northern Illinois. We expect high grub numbers to be spotty in occurrence in central and northern Illinois due to the reduced emergence of adult Japanese beetles and the abundant rainfall this summer.

Scout for grubs by cutting through the turf with a heavy knife and pulling it back to reveal the grubs in the root system. Till the upper two to three inches of soil with the knife to reveal deeper grubs, particularly in dry soil. Ten to twelve grubs per foot square is the general treatment threshold.

Zimmerman Pine Moth is treatable in southern Illinois towards the end of the first week of August with permethrin (Astro) sprayed on the trunk and major branches. The appropriate time to treat in central and northern Illinois is during the second half of August. There is at least a two-week window of treatment while the newly hatched larvae roam on the bark seeking an overwintering site.

Fall webworm, walnut caterpillar, yellownecked caterpillar, whitemarked tussock moth, and other late summer caterpillars are susceptible to control with Bacillus thuringiensis kurstaki (Dipel, Thuricide, others), acephate (Lepitect, Orthene), permethrin (Astro), other labeled pyrethroids, and other labeled insecticides. Realize that even severe defoliation at this time of year has little effect on tree health because the leaves have produced most of the sugars that they will produce this year. Treatments at this time are primarily for aesthetic reasons.--Phil Nixon, C.M. Dailey, Martha Smith

Phil Nixon

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