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Japanese Beetles Are Relentless in Many Areas of Illinois

July 12, 2002
The numbers of reports about problems with Japanese beetles have escalated during the past couple of weeks, and the reports just keep on coming . . . and coming . . . and coming (to paraphrase the Energizer bunny). The densities of this pest seem to be at an all-time high in many areas of Illinois. In some areas, Japanese beetles are showing up for the first time--and they're showing up with a vengeance. Defoliation of ornamentals and trees has been widespread, and defoliation of corn and soybeans continues. In previous issues we stated that defoliation of corn by Japanese beetles usually is not problematic. However, in fields in which corn is showing obvious signs of moisture stress (i.e., lack of moisture), heavy defoliation could exacerbate the problem, resulting in additional yield loss. Unfortunately we have no guidelines for treatment of Japanese beetles defoliating corn. Use your best judgment.

Most people are aware of the traps used to capture Japanese beetles. Not surprisingly, Ron Hines, senior research specialist at the University of Illinois Dixon Springs Agricultural Center, has decided to add Japanese beetle traps to his arsenal of traps for capturing insects. The area in which Ron works (Pope and Massac counties) has not had much of a history of infestation of Japanese beetles, but that situation has changed in 2002. Ron reported capturing about 600 and 300 beetles per trap per day in two different sites in Pope County. In Massac County, he was capturing about 80 Japanese beetles per trap per day. And apparently in an attempt to develop a threshold (or to keep a technician busy), Ron determined (from 28 100-beetle samples) that the average weight of 100 Japanese beetles is 8.25 grams, or 0.0825 gram per beetle.

Trap used to capture Japanese beetles at the University of Illinois Dixon Springs Agricultural Experiment Station. (Photo courtesy of Ron Hines.)

Representative capture of Japanese beetles in a trap at the University of Illinois Dixon Springs Agricultural Experiment Station. (Photo courtesy of Ron Hines.)

Certainly not to be outdone, John Lilienthal, with Pioneer Hi-Bred International, told me that during 1 1/2 days of operation of one Japanese beetle trap in the Kankakee area, he measured 6 gallons of beetles. Because these traps are effective for attracting and capturing Japanese beetles, large captures are not unusual. However, the numbers of Japanese beetles in Illinois this year seem to have reached historic proportions.

In previous articles about Japanese beetles in the Bulletin (issue no. 13 and no. 14, June 28 and July 5, respectively), we have provided details about thresholds and suggested insecticides. However, it's important to note that some frustrations with control efforts are likely. Because Japanese beetles emerge over time, an insecticide applied early may not last long enough to control later-emerging beetles. Also, when temperatures are high, pyrethroid insecticides (e.g., Ambush, Asana, Capture, Pounce, Warrior) may lose some efficacy. And when insecticides are applied during silking, the lengthening of the silks exposes silks on which insecticides are not present. All of these factors may challenge control of Japanese beetles, so be patient, and don't expect 100% control, which is not required to protect the crop.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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