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No. 12/June 15, 2001

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Soybean Aphids Reported in Minnesota Soybean Fields
On June 12, we received a report concerning observations of what appear to be soybean aphids in four soybean fields, all in the early vegetative stages of development. The soybean fields sampled were in Houston County, located in southeastern Minnesota. The sampled fields were located near other fields that had been heavily infested with soybean aphids in August of 2000.

If you find aphids in soybean fields, please report these observations to us as soon as possible.

Large Numbers of Corn Rootworm Larvae Reported in Some Cornfields
We have received a few reports of corn rootworm larval injury, in some cases from fields that were treated at planting with a soil insecticide. Evaluating soil insecticide performance for corn rootworm larval control requires a little effort. The questions and answers in this article are designed to provide some additional input on this topic.

Aren't corn rootworm larvae almost impossible to find?
If I find corn rootworm larvae, how concerned should I be?
When should I be concerned if I find corn rootworm larvae?
How do I grade the performance of my soil insecticide?
If I find very few rootworm adults in my cornfield in July, doesn't this suggest that my soil insecticide worked pretty well?
If I don't have any severe lodging in my field, is it safe to assume that my soil insecticide performed adequately?

First Flight of European Corn Borer Remains Unimpressive
The first flight of the European corn borer continues; however, the number of moths reported from several areas of the state suggests that the first-generation infestation may be very low. But although European corn borer moth numbers appear to be down, the corn borer moth flight remains impressive; this year's capture of southwestern corn borer moths for Massac County is approximately nine times greater than last year's moth flight.

Stalk Borer Injury Reported in Northern Illinois
Stan Eden has received several calls concerning infestations of stalk borers. Visits to nearby fields confirmed that corn plants were being infested by this insect pest. The areas of fields most severely affected were those that had been infested with giant ragweed last season. Many of the stalk borers are still very small, suggesting that migration from their weed hosts to corn is not yet complete. Producers are encouraged to consider the use of an insecticide in areas of fields that were heavily infested last season with grasses and other weeds, especially giant ragweed.

An Epitaph for Burrower Bugs
Burrower bugs have been observed in many cornfields and soybean fields, especially in southern Illinois. It is very unlikely that burrower bugs are creating any plant damage to corn and soybean plants. In fact, they are most likely doing producers a favor by feeding on weed seeds.

It's Time to Consider Monitoring Western Corn Rootworm Adults in Soybean Fields
The monitoring program is in its sixth year, and data from this program have shown that the new strain of western corn rootworm is now present in 40 counties in Illinois. Extension entomologists continue to recommend the use of the monitoring program to predict root injury in rotated cornfields and track the spread of the new western corn rootworm strain.

Striped Cucumber Beetles in Cornfields and Soybean Fields
We have received reports of striped cucumber beetles in cornfields and soybean fields. These beetles closely resemble western corn rootworm adults. Striped cucumber beetles do not cause damage to corn and soybean, so don't be alarmed by the presence of these beetles in your fields.

Early-Season Foliar Diseases--Soybean
Many areas of the state have received a lot of rain over the past week. Blowing wind and rain help move pathogens from plant to plant. Wet, cool soil in flooded fields increases sporulation and movement of many soilborne pathogens. Recent weather conditions will probably increase the likelihood of infection by foliar and soilborne pathogens in the coming weeks.

This article discusses Septoria leaf spot and sudden death syndrome (SDS).

Floppy Corn, or "Rootless Corn Syndrome"
Over the last month there have been a number of reports of corn plants "flopping in the wind" due to lack of nodal root development. Rootless corn usually develops when the nodal roots initiate growth at or near the soil surface.

It's always important to plant corn deep enough, and if rootless corn syndrome begins to develop, row cultivation may encourage root development when moist soil is thrown around the base of the plant.

Herbicide Considerations When Replanting
Excessive precipitation over the past two weeks has resulted in many new "ponds" appearing in fields where corn or soybean once grew. Replanting these areas will likely be done as soon as soil conditions allow. Previous herbicide applications should also be considered as replanting decisions are made. Nearly all corn and soybean herbicide labels list rotational intervals that should be followed to reduce the likelihood of rotational crop injury.

This article also contains advice to producers who are considering replanting these areas with soybean.

Preharvest Herbicides for Wheat
Few herbicides are cleared for preharvest applications in wheat. Clarity, glyphosate, and some formulations of 2,4-D are labeled for preharvest applications in wheat, but if you intend to plant soybeans after using one of these herbicides as a preharvest treatment, be sure to follow herbicide label precautions. Preharvest treatments in maturing wheat fields often require aerial application, and drift of any of these products out of the target area can seriously injure susceptible plants (crops, ornamentals, gardens, etc.).

Crops Respond to Warmer Weather
The corn crop has responded well to recent warm temperatures and the sunshine that has accompanied them. Leaf color has improved greatly, and with a few exceptions, much of the corn has entered the rapid-growth stage, with increases in height of several inches per day in many fields. As the crop is now showing, we probably did not lose much yield potential to the May weather, even though it often seemed more like March than May.

Soybean plants in most fields are still rather pale in color, as the nodules start to form. Wheat is ripening rapidly, and harvest is under way in the southern end of the state.

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 east-central, northern, southern, and west-central Illinois.

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

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