Figure 1. Bean leaf beetle adult on soybean. Photo: A. Varenhorst.
Overwintering Bean Leaf Beetles
The overwintering generation of bean leaf beetle adults emerge in the spring and can cause serious defoliation injury to seedling soybean plants (Figure 1). However, the abundance of overwintering bean leaf beetles is negatively affected when the air temperatures get too cold. Therefore, an estimate of the emerging populations can be made based on how cold the winter was.
The first step in calculating bean leaf beetle mortality is recording the air temperatures that drop below 14°F (-10°C). At these temperatures bean leaf beetle adults freeze and subsequently die. Although the adults can survive cold temperatures by hiding under plant debris and loose soil, especially in wooded areas, they cannot survive sustained sub-zero temperatures. Lam and Pedigo (2000) developed a survival model for the bean leaf beetle to predict overwintering population mortality. This model functions by accounting for the accumulation of sub-freezing temperatures (14°F or colder), and the known response of overwintering bean leaf beetles in both exposed (under crop residue in a field) and protected (residue in wooded areas) environments to such temperatures. Using this model, the predicted mortality rates for the overwintering bean leaf beetle populations in 2016-2017 winter in Eastern South Dakota ranged from 73-100% (Figure 2). This is increased from the 2015-2016 winter where the mortality ranged from 66-95%. Although mortality is expected to be high, there is still the potential for bean leaf beetles to emerge if they had adequate cover during the cold temperatures.
Figure 2. Predicted bean leaf beetle mortality in South Dakota for the 2016-2017 winter.
Growing Season Considerations
For the 2017 growing season, soybean farmers in areas with decreased bean leaf beetle mortality should focus on early season scouting for emerging overwintering adults. Scouting should begin at soybean emergence and continue through the early vegetative stages. This is especially true for soybeans that are planted early, and/or have had past issues with bean leaf beetle defoliation or Bean pod mottle virus transmission. The overwintering generation of bean leaf beetles can be effectively managed through the use of insecticide seed treatments.
- Hodgson, E. and A. Sisson. 2016. Predicted mortality of bean leaf beetle is low. Iowa State University Extension.
- Lam, W-K. F., and L. P, Pedigo. 2000. A predictive model for the survival of overwintering bean leaf beetles (Coleoptera: Chrysomelidae). Environmental Entomology, 29:800-806