No. 12 Article 7/June 16, 2006

More Insect Events of Note

Ron Hines, senior research specialist at the Dixon Springs Agricultural Center, reported captures of Japanese beetles at five of his six trap locations--Fayette, Massac, Pope, Pulaski, and St. Clair counties--during the week ending June 13. We should begin to observe Japanese beetle adults soon in central and northern counties. They may move first to flowering weeds and flowering plants around homes, but we’ll have to keep a watchful eye on pollinating cornfields and on soybean fields.

Ryan Stoffregen, Advanced Crop Care, noted a marked increase in armyworm activity in wheat in northern counties over the past week, with densities ranging from 1 to 2 larvae per foot of row (most common) to 4 to 5 per foot of row. The sizes of the larvae he found varied considerably, and most of the feeding was confined to the leaves on the lower half of the plant. However, as the larvae grow, they will continue eating leaves, moving upward toward the heads. If they begin devouring flag leaves or clipping the heads, yield losses may occur.

Few people encounter garden symphylans in corn, but these arthropods can cause noticeable injury. David Keimig, field sales agronomist with Pioneer Hi-Bred International, has found garden symphylans and symptoms of their injury in a couple of fields in northern Illinois. Injured plants were stunted, and the injury was most common in areas of the fields where the soil was very loose. Kevin Black, insecticide/fungicide technical specialist with Growmark, reported that an FS crop specialist also found garden symphylans causing injury to corn near Arlington. Garden symphylans are not insects, nor are they centipedes, despite their numerous legs (adults have 12 pairs of legs). They are small white arthropods, measuring 1/4 inch or less. They feed on the roots, often stripping root hairs. Injured plants often grow past the injury if growing conditions are suitable.

Stink bugs seem to be uncommonly common in some areas of Illinois this year. Matt Montgomery, crop systems Extension educator in Springfield, reported considerable stink bug injury in cornfields in Menard and Sangamon counties. He indicated that most of the injury was not economic, at least on a fieldwide basis, but that the injury was quite noticeable. Kevin Black also has received a fair number of reports of stink bug injury.

Stink bug nymph on a corn leaf (photo courtesy of Matt Montgomery, University of Illinois Extension).

Stink bug injury to corn (photo courtesy of Matt Montgomery, University of Illinois Extension).

We currently have no explanation for the increased frequency of stink bug injury in corn in 2006, but we’ll do what we can to determine any common threads among fields with injury.--Kevin Steffey

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