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Corn+Soybean Digest

Entomologist Predicts Corn and Soybean Insect Threats

As corn and soybean producers look ahead to a new growing season, a universal question arises: What insects will pose a threat to crops this year? Mike Gray, University of Illinois Extension entomologist, shares his predictions about Japanese beetles, soybean aphids, European corn borers and western corn rootworms.

Japanese beetle infestations will continue to vex producers this year, Gray says. Despite the cold winter, snow cover across many areas of Illinois most likely served as a buffer and enhanced the survival of overwintering grubs.

On the other hand, soybean aphid populations may be down. David Voegtlin, a retired entomologist with the Illinois Natural History Survey, says buckthorn leaves were “dripping” with aphids last fall.

“Not surprisingly, a fungal epizootic swept through this impressive aphid buildup on buckthorn and decimated the population,” Gray says. “Consequently, I anticipate a very small spring flight from buckthorn to soybean fields.”

The European corn borer reached all-time population lows across Illinois last year. With such low overwintering numbers, Gray expects the spring flight of these insects to hardly be noticeable.

Almost every year, the western corn rootworm causes some management challenges, Gray says. However, densities were low in 2009.

“Considerable speculation has arisen regarding whether or not the large-scale increase in Bt usage may be suppressing corn rootworm populations, similar to what happened with European corn borer densities,” he says. “Because Bt hybrids targeted at corn rootworms are considered low-to-moderate dose in their toxic effects, I suspect environmental conditions last season served as the major contributor to the collapse of the corn rootworm population.”

Gray says the wet soil conditions last spring resulted in high mortality of western corn rootworm larvae soon after hatch occurred. Thus, he expects light to moderate infestations this year.

It’s too early to assess the potential impact of insects that migrate into Illinois such as black cutworms, corn leaf aphids, potato leafhoppers, fall armyworms and corn earworms.

For more information, read The Bulletin online.

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