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No. 19/August 04, 2000

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Preliminary Root-Rating Results for DeKalb and Monmouth Corn Rootworm Trials
On July 24 and 25, a crew led by John Shaw, Illinois Natural History Survey, dug and washed roots from experimental corn rootworm trials in Monmouth and DeKalb, respectively. We rated the roots for larval injury and present some of the preliminary results in table form.

Most of the standard soil insecticide products we tested at these locations held up reasonably well to moderate rootworm pressure. Controls (no soil insecticide used) at each location were above a root rating of 4.0 (one node of roots or the equivalent destroyed). Although many of the products performed satisfactorily in our trials, consider that we did not plant corn until mid-May.

As we look back on this summer and examine how products held up to rootworm pressure in producers' fields, it becomes obvious that insecticide performance varied considerably from field to field. Many interacting factors are involved, including planting date, rainfall patterns and amounts, product characteristics, accuracy of application (calibration accuracy), and method of application (band vs. in-furrow). Our results also clearly show that seed treatments did not hold up very well at either location.

Continue Watching for European and Southwestern Corn Borers
The presence of moths indicates that egg laying is ongoing. It is possible that numbers of surviving larvae in some cornfields could be large enough to get our attention. This is especially true for late-planted corn. Even though the price of corn is low, heavy infestations of European corn borers might be worth controlling in fields with high-yield potential.

The southwestern corn borer is a distinctly more critical concern in southern Illinois. The potential for heavy infestations is significant.

Southwestern Corn Borer or Stalk Borer?
I received information of suspected southwestern corn borer larvae in a giant ragweed stem (Clark County) and a cornstalk (Adams County). Fortunately, the individual in Adams County had photographs of the insect, which convinced me that it was a mature stalk borer larva. The distinguishing characteristics of the two pests are the dark stripe on the head of the stalk borer and the large, dark tubercles all over the body of the southwestern corn borer. The people who had found the caterpillar in a giant ragweed stem in Clark County had confirmed that the insect was a mature stalk borer.

Because southwestern corn borers can be very damaging pests, proper identification of spotted caterpillars is very important.

Bean Leaf Beetles Are Easy to Find
In soybean fields and elsewhere, adult bean leaf beetles are fairly common right now. Symptoms of injury are apparent. However, no one has reported significant amounts of defoliation yet.

Of special interest is the possibility that bean leaf beetles might transmit viruses to soybeans. Researchers are investigating the relationships among bean leaf beetles, viruses, and soybean plants; and results of their efforts will be forthcoming this fall.

Sudden Death Syndrome on Soybean
SDS is here and has been reported in several areas of the state where rainfall has been plentiful. SDS also seen in isolated areas where beans were planted early in Adams County, despite recent dry conditions. Discusses symptoms.

Physoderma Brown Spot
Discusses symptoms, causal organism. The presence of this disease should not cause concern. It is not usually economically important.

Corn Diseases
Fungi: The common rust situation on field corn has slowed down somewhat, and currently the only other leaf blight that we have been seeing with any regularity is gray leaf spot.

Some virus symptoms are showing up in the corn in southern Illinois.

Soybean Diseases
Fungi: (Besides SDS;) white mold in irrigated soybeans.

Viruses: Reports of the beginning of virus symptoms in soybean. Most viral diseases in Illinois look very similar in the field. The only way to know for sure is to have them tested; with recommendations.

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.

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

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