Bean Leaf Beetles - in WI - in 2009?

Bryan Jensen, IPM Program

Here is what we think is going to happen in the spring of 2009. An overwintering bean leaf beetle mortality models suggests a second year of high mortality (>50%) of the overwintering adults. For more information on your specific area, please review DATCP Entomologist Krista Hamilton’s article in the May 8 edition of the Wisconsin Pest Bulletin (http://pestbulletin.wi.gov/index.jsp). 

Also bean leaf beetle numbers were relatively low, statewide, in 2008. High mortality of a low overwintering population would suggest a low probability of economic defoliation on seedling soybeans this spring. Especially when economic thresholds are relatively high (see Pest Management in WI Field Crops-2009, page 124, http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2009-P155C35.aspx).

The other factor to consider is transmission of bean pod mottle virus (PBMV). DATCP typically runs a PBMV survey on overwintering adults collected from alfalfa and it will be good to see those results. However the good news is that incidence of PBMV has been low in 2008.

What does this mean for 2009? Although the early indications are for a light overwintering population, there is still a need to spot check early emerging soybean fields. Overwintered adults initially feed on perennial legumes, like alfalfa and other clovers, before migrating to (and sometimes concentrating) in early emerging soybeans. Identify those early planted fields in your area and make a point to scout them soon after emergence. This approach can give confidence in and verify predictions……or give you time to react if predictions are wrong.