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No. 15/July 07, 2000

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Evaluating Corn Roots for Rootworm Larval Damage
It's now time to talk about rating roots for rootworm damage. This article offers an explanation for the Iowa State University 1-6 root rating scale. Schematic illustrations of root ratings 2, 3, 4, and 5 are included, as well as a brief video of the root rating process.

Some cornfields in western Illinois are showing signs of severe rootworm larval damage. As July progresses, we may receive more reports of such damage. In fact, if rains continue to loosen the soil and if wind becomes a factor, some corn plants may lodge as a result of severe rootworm larval damage. However, always remember that other factors can cause corn plants to lodge; only by examining the roots can you verify the presence or absence of rootworm damage.

Western Corn Rootworm Field Days in McLean and Menard Counties
This article provides some additional information about the field days for the western corn rootworm monitoring program scheduled in McLean and Menard counties.

Japanese Beetle Densities Remain Impressive: Don't Forget to Monitor Fields for Silking Clipping
Like many of the other grub species that have plagued Illinois producers this spring, the Japanese beetle promises to be no exception. In the coming weeks of July, corn growers are urged to monitor their pollinating fields for Japanese beetle adults and their silk clipping activities. In August, producers will increasingly turn their attention to soybean fields and defoliation caused by this insect pest.

Scouting efforts should be well under way for Japanese beetle adults during this silking and pollination period of corn development.

Fungal Leaf Diseases on Corn
This article describes several fungal leaf diseases on corn, including common rust, southern rust, physoderma brown spot, anthracnose, and eyespot. What is important to remember about all these leaf blights, including the rusts fungi, is not the individual identity of which blight you have but rather the percentage of leaf area blighted as a whole on your entire plant; control considerations may be justified when whole-plant infection reaches 15%. Note that the type of symptoms or size and coloration of lesions for these corn leaf blights can vary with the genetic resistance of the hybrid that you plant.

What's Ahead for the Corn Crop?
In most areas of Illinois, rainfall has been adequate to allow the corn crop to approach pollination in good shape, with enough stored soil moisture to carry the crop through pollination and into the start of grainfilling. Although moderate temperatures the past 2 weeks have slowed the race toward pollination a little bit, many fields in the central part of the state are fully into the silking stage, and some have probably completed the pollination process.

A sudden onset of hot, dry weather can still cause some damage, especially to those crops that haven't yet tasseled. But if grainfilling starts early and takes place during warmer weather, it will also occur more rapidly, and physiological maturity should come early.

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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