No. 14/June 30, 2000

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Get Ready for Rootworm Adults
More reports regarding emergence of adult western and northern corn rootworms came in during the week of June 26, so we can assume that emergence will be in full swing all over the state within the week. The presence of emerging adults also means that larvae are completing their development, and the amount of root damage in any given field will be at its zenith soon.

You can begin assessing corn roots for rootworm larval damage right now. As pollination begins in various regions of the state, you should be alert for large numbers of rootworm adults. If they clip enough silks, they can interfere with pollination.

This article lists suggested insecticides for control of corn rootworm adults.

Field Day Scheduled to Promote Western Corn Rootworm Monitoring Program
In 1998, University of Illinois Extension entomologists unveiled a monitoring program for adult western corn rootworms (WCR) in soybean fields to predict root injury in rotated corn. The monitoring program is in its third year, and data from this program have shown the new strain of western corn rootworm is now present in 26 counties in Illinois. To learn more about this monitoring program, growers are invited to attend a field day: July 7, Arthur, Illinois; July 13, Petersburg, Illinois; and July 14, Bloomington, Illinois.

First Report of Japanese Beetles
Many of us will remember the very large numbers of Japanese beetles that occurred in corn and soybeans last year, especially in eastern and central Illinois. We need to be ready for them again because early indications suggest they may be numerous in 2000.

Japanese beetles have been reported around homes and gardens in most of the major cities in Illinois. Therefore, we should anticipate that they will show up in nearby crop fields and possibly spread from there.

The greatest concern regarding Japanese beetles is their feeding on soybean foliage. Although no one has reported finding Japanese beetles in soybean fields yet, you should be aware of the threshold, just in case the beetles show up in soybeans soon.

Corn Leaf Aphids in the Whorls of Corn Plants
Winged corn leaf aphids have been found in the whorls of corn plants across a wide area in the northern half of Illinois during the week of June 26. They might have been recently blown into Illinois on the storm fronts that have passed through. Large numbers of corn leaf aphids are usually associated with droughty conditions, which certainly do not exist in most areas of Illinois. However, corn leaf aphids are capable of increasing their numbers dramatically.

Status of First-Generation European Corn Borers
We still have heard very little in the way of significant numbers of first-generation European corn borers in 2000.

For the most part, the first generation of the European corn borer will come to an end soon in southern Illinois. But don't be lulled to sleep; the second generation still deserves our attention.

Plenty of Southwestern Corn Borers in Some Counties
Recent mild winters have allowed the southwestern corn borer to thrive in our southern counties, and it has caused far more concern than the European corn borer. Numbers of southwestern corn borers this year are fairly large in some areas.

Entomologists debate whether first-generation southwestern corn borers cause economic damage. But regardless of your take on this issue, the second generation of this important insect pest is worth your attention if you live or work south of I-70.

Wheat Streak Mosaic Virus in Field Corn
Shawn Kaeppler (from the University of Wisconsin) and others recently published some work looking at the interaction of wheat streak mosaic virus (WSMV) and high plains virus (HPV). In the study, they looked at the virus symptom development and how well the virus replicated in the plant for each virus singly and in combination.

Most of our currently grown hybrids do not have susceptibility to the virus, but some inbreds do. And the study showed that the virus replicated well in the tissue despite the absence of lethal symptoms.

Two things could happen. First, the corn can serve as a green bridge to keep the virus around until the winter wheat is planted. Second, if either maize chlorotic mottle virus (MCMV) or high plains virus (HPV) should by some unfortunate circumstance move their way into the state, some very "lethal" damage can develop on the corn if the corn plants are acting as a nonsymptomatic host for WSMV.

Fungal Leaf Disease Showing Up in Corn
Common rust on field corn is here. It seems that about every 5 or 6 years it shows up early in the season in field corn and causes concern. We have reports of active common rust in the northwestern and west-central parts of the state.

How can you make a reasonable decision about treatment? First, consider the weather. Next, consider the probability of other fungal leaf blights developing in the field. You need to know the probability of other fungal diseases developing because there's not a big arsenal of fungicides for treatment.

Alert: Toxic Ergot Prevalent in Brome Grass and Rye This Year
Ergot is very prevalent along unmowed fencerows and in pastures this year. Ergot is a fungal disease of the seed head of about 200 wild and cultivated grasses and opened-pollinated small grains like rye.

Infested grain is a concern because the fungus produces very potent toxins that affect both humans and animals. Grasses should be inspected for ergot before allowing grazing this year.

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 Illinois and west-central Illinois.

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

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