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ISU notes counties at risk for soybean diseases

By Staff | Jun 4, 2010

ANKENY -Soybean farmers in 16 Iowa counties may have fields at risk this summer from a soybean virus called bean pod mottle virus, according to a model developed at Iowa State University.

Transmitted by hungry bean leaf beetles, BPMV is one of the most prevalent viral soybean diseases in the United States, posing a risk to soybean production by reducing yield and affecting quality.

The counties identified by the ISU Pre-Plant BPMV Prediction Model to be at moderate risk are Cedar, Clinton, Des Moines, Henry, Jefferson, Johnson, Keokuk, Lee, Linn, Louisa, Marion, Muscatine, Osceola, Scott, Wapello and Wayne.

All but Osceola are located toward the southeast part of the state.

“Soybean growers in those counties are cautioned to use recommended best management practices for bean leaf beetle control to minimize the impact of the disease,” said Forrest Nutter, an ISU plant pathologist.

The ISU Pre-Plant BPMV Prediction Model is based on a three-year, soybean checkoff-funded study that showed BPMV incidence (risk) was related to the number of days between Oct. 1 and April 30 with mean daily temperatures below 32 degrees.

The fewer days with temperatures below 32 degrees, the higher the survival rate for bean leaf beetles and, therefore, the greater the risk of BPMV.

“Using this model, we have identified which counties may be at risk for BPMV incidence in 2010 because those counties experienced fewer days with temperatures below freezing last winter,” Nutter says. “Since overwintering and first generation bean leaf beetle populations are the most important factor in the spread of BPMV, a number of management practices are recommended.”

Insecticide seed treatments have proven to be an effective management tool to control first generation bean leaf beetles, thus reducing the transmission of BPMV from beetle to plant. Until recently, insecticide seed treatment decisions had to be made without knowing the likely risk of BPMV, but with the Pre-Plant BPMV Prediction Model, growers can make bean leaf beetle and BPMV management decisions with a higher level of certainty.

In counties identified as being at risk, Nutter said, soybean growers should conscientiously scout to detect areas where bean leaf beetle populations may be high enough to warrant mid-season foliar insecticide control measures, noting that early planted soybean fields have higher risk of BPMV incidence. For best results, farmers should follow the ISU economic threshold for bean leaf beetle management.

“For the rest of Iowa, given the low predicted risk, overwintering and first generation bean leaf beetles are likely to be too low to warrant the need for seed or foliar insecticides,” Nutter said.

He cautions, however, that the model only targets bean leaf beetles and is not meant to predict the risk of other pests such as aphids.

In addition, Nutter notes soybean fields in low-risk counties should still be scouted routinely for bean leaf beetles, as there may have been pockets where the depth and duration of snow cover was sufficient to provide insulation for bean leaf beetles to survive.

To learn more about managing bean leaf beetles, go to www.planthealth.info.

The Iowa Soybean Association develops policies and programs that help farmers expand profit opportunities while promoting environmentally sensitive production using the soybean checkoff and other resources. The Association is governed by an elected volunteer board of 21 farmers.

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