By TIM ALEXANDER

Illinois Correspondent

EAST PEORIA, Ill. — Central Illinois farmers should carefully consider their insecticide treatment programs, especially regarding western corn rootworm (WCR), on a field-by-field basis this year.

According to Michael E. Gray, professor and assistant dean for the University of Illinois Department of Crop Sciences, as concerns mount over WCR resistance to some Bt proteins such as Cry3Bb1 and mCry3A, farmers are using more planting-time soil insecticides and Bt hybrids to reduce the risk of yield losses. But with farm profit margins anticipated to be much narrower than in recent years, he urged farmers attending the U of I Corn and Soybean Classic Jan. 7 to consider the necessity of employing that strategy in their fields this growing season.

Not only can such a dual approach be costly, but recent research by land grant scientists at the U of I, Iowa State University and the University of Nebraska suggests the strategy may actually hasten the onset of resistance to Bt proteins, Gray told some 200 producers in attendance.

“We have a large WCR research program and several test plots at the University of Illinois, where we challenge soil insecticides and challenge Bt hybrids to see how well they stand up to WCR. In our 2014 corn rootworm trials, soil insecticides by themselves did a pretty good job,” he said.

“Looking forward to the 2015 growing season, you should carefully evaluate whether or not the combined approach of Bt rootworm hybrid and planting-time soil insecticide makes sense for your operation.”

Studies have shown densities of WCR adults in corn have been greatest in east-central Illinois during the last couple of years compared with other areas of the state. Gray advised that when beetle numbers reach or exceed 0.5 per plant on first-year corn or 0.75 in continuous corn, larval injury the following season may lead to economic losses without the use of management inputs and/or crop rotation.

Producers should carefully scout their cornfields for WCR this summer and critically evaluate the potential return on investment regarding the use of a Bt rootworm hybrid in 2016. A rescue treatment should be considered when five or more beetles per plant are found, silks have been clipped to one-half inch and pollination is ongoing, the U of I entomologist advised.

“I am asking growers to consider their input decisions that they want to put into this crop, because margins are going to be pretty tight this year,” Gray pointed out. “Profit margins are likely to be narrow due to rising input costs, the record 2014 harvest and subsequent weak outlook for corn prices.

“By making more informed choices about insect management, some farmers will be able to maintain a competitive advantage.”

Using inputs that have not been proven in field trials to be beneficial to larvae and insect management – and may hasten resistance development – will cut into profits and potentially cause additional harm. Scouting fields, becoming familiar with economic thresholds, integrating effective management tactics and thinking beyond the current growing season will place producers at a competitive advantage over those who do not employ such tactics, Gray concluded.

During an interview following his presentation, he reiterated the importance of farmers checking their fields diligently for WCR and other pests capable of causing economic losses at harvest.

“Quite honestly, it seems like a lot of times growers really don’t see rootworm injury until it’s too late, sometimes at harvest. By then, you’ve got a lot of root rot and it’s not an ideal situation to be in by that point,” he said.

Tips on management strategies for WCR in soybeans, bean leaf beetles, Japanese beetles and northern corn rootworm were also provided by Gray. His recommendations, along with the results of the 2014 WCR trials, may be accessed at the U of I http://farmdoc.com website.