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No. 20/August 18, 2000

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Corn Rootworm Larval Injury Evaluated in First-Year Cornfields
In late July, Susan Ratcliffe, Extension entomologist, coordinated a large root-retrieval project. We extend our thanks to all those who participated. Ultimately, we hope to refine our economic threshold even more when these data (presented here in table form) are further evaluated.

A cursory examination of these preliminary data reveals considerable variation in root injury from field to field. These data show that only 13 of 36 fields exceeded the economic injury index of 3.0 in untreated check strips.

Keep Your Eye on European Corn Borers
As a follow up to last week's story, note that Alan Mosler with Twin Counties FS indicated on August 4 that second and third instars were present throughout southern counties and that boring into stalks was imminent.

For the rest of the state, it's worth noting that European corn borer adults are rather common. I have also heard of small pockets of significant infestations in several areas of the state.

Blister Beetles in Corn, As Well As Alfalfa and Soybeans
Dennis Epplin, crop systems educator in Mt. Vernon, recently reported blister beetles stripping some corn plants, including the silks, in a cornfield in Jefferson County. He had been finding intense, localized infestations of blister beetles in alfalfa and soybeans earlier this summer, but the infestation he encountered in corn was the most severe. Although the infestation was not economic (from a whole-field perspective), the injury was devastating in small areas of the field.

Description of the beetle provided and pictures in the Web version.

We consider blister beetles to be more beneficial than pestiferous (although their presence in alfalfa hay is a notable exception). Therefore, it's best not to overreact to their presence, even though injury to the plants can be quite severe in areas of the field where the beetles congregate.

Cotton/Melon Aphids in Soybeans in Northern Illinois
Here's one for the record books: cotton aphids (also known as melon aphids) in soybean fields in Illinois. John Wedberg, Extension entomologist at the University of Wisconsin had first observed aphids in soybeans in the southern tier of counties in Wisconsin in late July.

We also have received reports of these aphids in fields of soybeans in some counties in northern Illinois, including Kane and Grundy counties.

Description provided, what to watch for, possible treatments.

We'll provide updates as appropriate.

Diplodia Ear and Stalk Rot
The time is here for early ear-rot and stalk-rot development. Eric Suits of Trisler Seed reports diplodia ear rot reaching about 6% to 7% in some fields near Allerton and Sidell. Environmental conditions this season have set the stage for good development of ear and stalk rots. Specifically, look in fields that were affected earlier in the season by common rust infection and in fields showing nitrogen deficiency.

Description of diplodia ear rot, scouting procedures.

Midseason Soybean Problems
Frogeye leaf spot. Fungal leaf diseases are beginning to show up in the soybean crop. Omar Koester of the Monroe/Randolph Extension Unit reports very significant frogeye leaf spot in many area fields.

Frogeye leaf spot used to be common in the southern part of the state, but use of resistant varieties decreased the prevalence of the disease. However, in the past several years, frogeye leaf spot has been showing up more frequently.

Description; discusses why it may be increasing.

Sudden death syndrome. Bill Tarter of Alvey Labs reports the disease is showing up frequently in all of the central-southwestern counties. Environmental conditions have been very favorable for infection and development of SDS this season. If we enter a weather period that places the crop under some stress, expect symptoms to show up rapidly.

Regional Reports
Extension Center educators, Unit educators, and Unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season. This week's issue includes reports from northern and west-central Illinois.

SPECIAL REPORT: New Soybean Insect Pest Discovered in Northern Illinois, Wisconsin, and Michigan
During the past several weeks, increasing numbers of producers have discovered that their soybean fields are infested with aphids. These aphids were preliminarily identified as cotton or melon aphids. Last week, an entomologist with the Illinois Natural History Survey identified them as soybean aphids, Aphis glycines. These aphids, which are being found in soybean fields in northern Illinois, Wisconsin, and Michigan, have never been reported in the United States. They are native inhabitants of China, and their route of entry into the United States has yet to be determined.

This article contains additional information about the life cycle of these aphids, and it discusses control options.

Soybean Aphid Update: Preliminary Results of Insecticide Efficacy Trials
Questions concerning the wisdom of applying insecticides to rescue soybean fields infested with soybean aphids persist. An Extension Entomologist with Michigan State University recently reported the results of an unreplicated insecticide strip trial in Ottawa County, Michigan. This article describes the findings of that trial.

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

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