Western bean cutworm (Striacosta albicosta) in Michigan dry beans

Michigan is the second highest dry bean producer in the country, with a reputation for high quality beans. The western bean cutworm, Striacosta albicosta (Smith), is native to the western United States. In 2006, western bean cutworm (WBC) was first found in Michigan through a network of pheromone traps. From 2007 to 2011, the number of WBC continued to increase and the range expanded to cover the entire state. As WBC established itself as a pest in dry beans, the overall objective was to develop management recommendations for Michigan dry bean growers. This involved 1) Maintaining a trapping network to determine the timing of peak flight, 2) Finding where larvae are and when they feed in dry beans, 3) Determining how long pyrethroid residues last on dry bean foliage, and 4) Monitoring the percent hatch and percent parasitism of egg masses. We found that larvae feed at night and are in the blossoms, pods, or on the ground during the day, which makes them relatively mobile and difficult to scout for. Based on this behavior and our determination of peak flight, we decided that pesticide applications of a pyrethroid one to two weeks after peak flight gave the best control. Larvae were affected by pyrethroid residues up to 14 days after application. In 2010, we first saw egg masses that were affected by fungal pathogens, which resulted in 78% hatch. In 2011, we first saw egg masses that were parasitized, which resulted in 80-85% hatch. In 2012, we had egg masses that were affected by pathogens and parasitized, which resulted in 44% hatch. Due to these studies and recommendations, Michigan’s dry bean industry has had better management and a higher quality product.