No. 2 Article 2/April 9, 2010

Key Corn and Soybean Insect Outlook for 2010: What Should Producers Anticipate?

Accurately predicting what insects may do before corn and soybeans have been planted is always tough, but I'll offer some thoughts for a few key insect pests of those crops. Of most entomological interest in soybean is the soybean aphid. Many of us remember the swarms of soybean aphids across central and southern Illinois late in the growing season last year. They were abandoning soybean fields and seeking out their overwintering host-buckthorn plants. Based on observations by David Voegtlin, a retired entomologist with the Illinois Natural History Survey, buckthorn leaves were "dripping" with aphids following the growing season (late summer to early fall). Perhaps not surprisingly, a fungal epizootic swept through this impressive aphid buildup on buckthorn and decimated the population. Consequently, I anticipate a very small spring flight from buckthorn to soybean fields.

Once again last year, we reached all-time population lows for the European corn borer across Illinois. Densities were slightly larger in some areas of western Illinois. With such low overwintering numbers, the spring flight of European corn borers should be hardly noticeable in 2010 throughout Illinois. It seems that western corn rootworms create management challenges almost every year, through either root pruning or silk clipping. However, in 2009, their densities were very low. Considerable speculation has arisen regarding whether the large-scale increase in Bt usage may be suppressing corn rootworm populations, similar to what has been witnessed for European corn borer densities. Because Bt hybrids targeted at corn rootworms are considered low-to-moderate dose in their effects on corn rootworms, I suspect that environmental conditions last season contributed to the collapse of the corn rootworm population. Specifically, the very wet soil conditions throughout the spring resulted in high mortality of larvae soon after hatch occurred. Consequently, I believe many Illinois producers in 2010 should experience very light to moderate infestations of western corn rootworms.

Japanese beetle infestations will continue to vex producers in 2010. In spite of the very cold winter, the snow cover across many areas of Illinois should serve as a buffer and enhance the survival of overwintering grubs. Last year Andy Morehouse, a graduate student in the Department of Crop Sciences, conducted the first year of his thesis research in many producers' fields across Illinois. After the first year, his results clearly indicate that sampling only margins of a soybean field should not form the basis of a treatment decision for the entire field. It was common for densities of Japanese beetles to be impressive in field margins and quickly fall below economic levels in field interiors. Andy intends to conduct his second year of field research this season.

For many insects that migrate into Illinois (e.g., black cutworms, corn leaf aphids, potato leafhoppers, fall armyworms, corn earworms), it's too early to assess the potential impact on production this season. I look forward to sharing observations from around the state and region this summer with respect to insect infestations.--Mike Gray

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