By Adam Varenhorst and Philip Rozeboom et.al
Each year we evaluate the overwintering success of bean leaf beetles in South Dakota. For adult bean leaf beetles that successfully overwintered, emergence will begin in the spring and they will move into soybean fields. At this time, the overwintering adults will begin feeding on the seedlings with the potential to cause serious defoliation injury (Figure 1). However, the population density of overwintering bean leaf beetles is negatively affected by cold winter air temperatures. Knowing the amount of days that the air was cold enough to cause bean leaf beetle mortality allows us to estimate the emerging populations in the spring. 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. Snow cover increases the likelihood of bean leaf beetle survival even when temperatures drop below 14 °F.
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.
South Dakota Predicted Mortality Rates
Using the previously mentioned model, the predicted mortality rates for the 2025-2026 overwintering bean leaf beetle populations in Eastern South Dakota ranges from 73% to 100% .
Source : sdstate.edu