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No. 17/July 21, 2000

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Preliminary Root-Rating Results for Urbana Corn Rootworm Trial
On July 13, a crew led by John Shaw, Illinois Natural History Survey, dug and washed roots from an experimental corn rootworm trial located just south of Champaign-Urbana. We rated the roots for larval injury and present some of the preliminary results in table form.

Most products performed very well and kept larval injury below a root rating of 3.0 (some light pruning of corn roots) on the Iowa State 1-to-6 injury scale. The level of rootworm "pressure" in the experiment was quite good, with over two nodes of roots destroyed in the untreated control.

On July 24 and 25, we will continue our corn rootworm insecticide efficacy plot evaluations in Monmouth and DeKalb, respectively. As soon as data from these experiments are available, we'll share them with you.

Scouting for Corn Rootworm Adults
Emergence of corn rootworm adults is in "full bloom" throughout Illinois; peak population densities and peak egg laying will occur within the next few weeks. Therefore the time for scouting for rootworm adults is upon us. There are three different reasons for scouting for adult corn rootworms throughout most of state and a fourth reason in the counties in Illinois where western corn rootworms lay eggs in soybeans.

Includes guidelines for scouting for rootworm adults in corn (two different objectives) and soybeans.

Sudden Death Syndrome on Soybean
Sudden death syndrome (SDS) is a disease reported in most of the soybean growing areas of the United States and the world. The soilborne fungus, Fusarium solani f.sp. glycines, which is the causal organism of SDS on soybeans, infects soybean roots. Under severe conditions, SDS can result in flower and pod abortion, premature defoliation, and yield losses. The use of fungicides to control this pathogen has not been effective, and crop rotation does not provide a viable control alternative. Although SDS potentially can be controlled by host-plant resistance and some progress has been made in developing resistant varieties, screening for resistance is difficult because disease expression is often environmentally controlled. Disease surveys conducted around the state have shown that sudden death syndrome occurs more frequently in fields under high production, in wet and compacted areas, and in fields with high populations of soybean cyst nematodes.

Discusses symptoms, current management approaches to take.

Behold White Mold?
Because much of the Illinois soybean crop is in the reproductive phase, it's time to watch for several midseason diseases. Although I have not heard of any reports of white mold in Illinois at this point, should growers in the northern half of the state experience cooler weather along with continued rainfall, white mold may once again rear its ugly head in Illinois.

White mold is favored by moderate temperatures (less than 85°F), normal or excessive rainfall, and high canopy humidity. The first symptoms of white mold generally appear during growth stages R1 through R3 (beginning bloom through beginning pod) and are often aggregated (found in "hot spots") rather than uniform across the field.

Due to the depressed crop price, it is very unlikely that fungicide applications are economical.

Keep Your Eyes Open for Soybean Stem Canker
Stem canker symptoms usually appear in late July or early August, when the pods are starting to fill out, and persist until the crop matures. The fungus is favored by warm temperatures, normal or excessive rainfall, high canopy humidity, and crop damage (for example, due to hail). Discusses symptoms.

Phytophthora root rot has plagued a number of growers this season, and in terms of future variety selection it is important that Phytophthora and stem canker not be confused with each another (see Table 2 for comparison).

Fifty years ago, stem canker was a major problem. However, most varieties available today have good resistance to this disease. If you are experiencing problems with stem canker in certain areas or with certain varieties, consider tillage and rotation to reduce the amount of infested residue, and consider using other varieties that have a good track record against stem canker.

Due to the depressed crop price, it is very unlikely that fungicide applications are economical. There is a checklist on page 110 of the Illinois Agriculture Pest Management Handbook 2000, which will help you determine if a foliar fungicide application should be made to soybean fields.

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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