Issue 11, July 2, 2009

Japanese Beetles

After last week's article on Japanese beetle adults, I received several reports of sightings in northern Illinois. I appreciate these reports as it helps keep me up-to-date. Japanese beetle adults were found on June 26 in central Lee County, June 27 in northeastern Kendall County, June 29 in southwestern Ogle County, and July 1 in DuPage County. Thus, the beetles are out in northern Illinois.

Historically, Japanese beetle adults emerge in northern Illinois just before the Fourth of July holiday. I predicted emergence just after the holiday last week based on northern Illinois generally have pest events about two weeks later than central Illinois. With Illinois being about 400 miles long, pests generally emerge over a four week time span from Cairo to Rockford.

It is still too early to tell even in central Illinois about the numbers of Japanese beetle adults that will be present this year. It appears that their numbers will be high again this year in southern Illinois based on limited scouting conducted on June 29 in Murphysboro. One report from Monmouth indicates relatively high numbers, but this may not hold true throughout northern Illinois. Historically, the Illinois River valley appears to dampen the effects of cold winter temperatures with soils not freezing as deeply in that area. There are commonly higher populations of insects that are winter temperature sensitive in that area of western Illinois.

Keep scouting for beetle numbers and treat if populations are high enough to create significant damage. Remember that preventing early damage can result in less damage throughout the season. You might be ahead to spray if in doubt, but lower populations may allow you to eliminate follow-up insecticide sprays. Our recommendations for insecticidal control were covered in last week's newsletter.--Phil Nixon, Dale Baird, Alice Cassens, Jeff Rugg, Martha Smith, Morton Arboretum

Phil Nixon

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