D3095: Effect of planting date on seasonal timing of pest complexes and insecticide efficacy in soybean

Mid-Atlantic growers are planting full-season soybeans earlier, and regardless of planting date, some are mixing an insecticide into the postemergence herbicide application (6-8 weeks after planting). However, this application may not coincide with insect pressure and does not overlap with the most vulnerable soybean stages. To examine the impact of planting date on pest pressure and pesticide efficacy, we conducted a fully crossed field experiment with two planting date treatments (as early as possible and one month later) and two post-emergence pesticide treatments (herbicide only and herbicide with insecticide) at two research farms. During the season, we measured plant growth, pest and beneficial activity abundance, and the incidence and severity of plant and pod damage. At harvest, we measured yield. In the first year of this two-year study (2022), mean plant defoliation was below economic injury levels for all time points and treatments, and pod damage was below the management threshold for all treatments. Two weeks post-application, insecticide did not decrease the number of pests or beneficials in the earlier planting. In the later planting, we saw a 30% decrease in pests but also a 68% decrease in beneficials. Planting later resulted in no yield benefit, and only a 2.7% increase in the fraction of undamaged pods. Including an insecticide caused no change in yield or pod damage. Our data suggests that planting later in the season may increase the value of a post-emergence insecticide application, but it also increases non-target effects and did not translate to economic gains.