Bean leaf beetle adults are susceptible to cold weather and most will die when air temperatures fall below 14°. However, they have adapted to winter by protecting themselves under plant debris and loose soil.
Each spring, adult beetles emerge from overwintering habitat and migrate to available hosts, such as alfalfa, tick trefoil and various clovers.
As the season progresses, bean leaf beetles move to preferred hosts, like soybean, according to a news release from the Iowa State University Integrated Crop Management team.
While initial adult activity can begin before soybean emergence, peak abundance often coincides with early-vegetative soybean.
An overwintering survival model developed at Iowa State University in 2000 is helpful for predicting winter mortality based on accumulated subfreezing temperatures. Predicted mortality rates in Iowa are variable for the 2018-19 winter, ranging from 73-99%. Northern Iowa experienced colder temperatures and most bean leaf beetle adults are not expected to survive (99% mortality expected).
Overwintering beetle populations are expected to be low this year; however, consider scouting soybean fields, especially in southern Iowa, if:
- Soybean is planted near alfalfa fields or if the field has the first-emerging plants in the area. Overwintering adults are strongly attracted to soybean and will move into fields with emerging plants.
- Fields are planted to food-grade soybean production or are seed fields where reductions in yield and seed quality can be significant.
- Fields have a history of bean pod mottle virus.