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Notes on Other Insects

July 17, 2003

As summer rolls along, some insects pick up steam, while others lose steam. Following are some insect information capsules that summarize the current and pending status of insects still on our radar screen.

Bean leaf beetle. Beginning the week of July 7, we started to receive reports of first-generation bean leaf beetles emerging in soybean fields in central and northern Illinois. Thus far, their feeding activity has been overshadowed by the presence of Japanese beetles. However, bean leaf beetles are capable of causing considerable defoliation all by themselves. In addition, concern about bean pod mottle virus (real or imagined in Illinois) has some growers on edge. Many growers remember the large numbers of bean leaf beetles that occurred in their soybean fields late last summer, and the memory lingers. Keep in mind, however, that second-generation beetles were the cause for concern last year, not first-generation beetles. As more about bean leaf beetles and bean pod mottle virus unfolds, we'll keep you apprised. In the meantime, please try to keep this perceived problem in perspective.

Soybean aphid. The heavy rains that fell in northern Illinois during the week of July 7 had a negative effect on some populations of soybean aphids. As you will recall from previous articles in the Bulletin, infestations of soybean aphids were relatively widespread in northern Illinois, and natural enemies seemed to be on vacation. (With the low densities of soybean aphids in 2002, multicolored lady beetles had less food to eat, so their populations were lower, too.) However, Steve Doench, agronomist with Pioneer Hi-Bred International, reported that many soybean aphid populations have "crashed" as a result of the heavy rains. He did note, however, that some infestations remained fairly high, especially in Bureau, Carroll, Lee, and Whiteside counties. So keep tabs on population changes (increases or decreases) as the season advances. Many soybean fields are approaching or are in the R1-R2 stages of development, the critical time for assessment of soybean aphid densities. If a decision to apply an insecticide is made, please keep in mind the importance of protecting bees that are visiting soybean flowers. Refer to comments about this in the article "Questions About Japanese Beetles Abound."

Twospotted spider mite. Despite recent rainfall in some areas, pockets of two-spotted spider mites are apparent in some fields that have not been blessed with plenty of moisture. Kevin Black, with Growmark, reported that a small area of Warren County has some soybean fields infested with spider mites. At this time of year, a number of factors can cause soybean leaves to turn yellow. You should check suspicious yellow areas to determine the cause. If twospotted spider mites are causing the yellowing, their populations can be dealt with relatively easily with well-timed spot treatments of insecticides, assuming the infestation is not field-wide. Injury caused by twospotted spider mites in soybeans begins with yellow stippling, followed by browning of the leaves, and, ultimately, leaf necrosis if the densities of spider mites are high. Look for the little creatures (adults are 0.3 to 0.4 mm long) and their webbing on the undersides of soybean leaves. An extended period of hot, dry weather will allow their populations to increase in size, and the con-sequences, as we have learned from past experience, can be significant.

Keep the reports coming. Many times, you are our eyes and ears in the field. We'll be embarking on a few weeks of concentrated fieldwork soon, so it's really important that we stay in touch with what's happening around the state. We sincerely appreciate your willingness to share your observations. --Kevin Steffey

Author: Kevin Steffey

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

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