Bean Leaf Beetles in Soybean; Flea Beetles in Field Corn

Published: June 1, 2009

Bean leaf beetle adults leaving overwintering sites or moving from alfalfa fields after infesting them early season generally move to soybean fields. These beetles are capable of flying long distances and will seek seedling soybean plants on which they will feed, mate, and then oviposit eggs in the soil for the next generation of beetles. During this past week, bean leaf beetle numbers approached or exceeded economic levels in some Northern Missouri soybean fields. Most fields were early planted and received much precipitation following planting. Economic infestations of beetles were found in fields with and without insecticide treated seed. Insecticide trials conducted in Missouri and other states show that Cruiser and Gaucho are both very effective at controlling this insect pest under most environmental conditions. The problems encountered with control of early season bean leaf beetle in these few fields may be due to several factors including the long period of time between planting and the appearance of the beetles, the dilution of the insecticides by continuous wet soil conditions, or by excessive numbers of beetles migrating into these fields. We know first planted fields typically attract high numbers of beetles. In addition, laboratory research from Minnesota and field trials from Missouri, Nebraska and other states show that under normal conditions seed treatments are very effective at early season insect control for about a 45-day period followed by a reduction in efficacy over the next few weeks. It is likely that all of these factors had some influence on the economic infestations of bean leaf beetle adults observed in northern Missouri soybean fields. The following insecticides are recommended for bean leaf beetle control in soybean.

Similar to bean leaf beetle, some flea beetle problems were observed on corn plants produced from both nontreated seed and seed treated with the 250 rate of insecticide. Flea beetles often damage corn grown from nontreated seed if beetle populations are high coming out of winter. In contrast, plants from insecticide treated seed rarely experience problems with this early season pest. The factors discussed previously with bean leaf beetle are likely reasons for the economic damage seen with flea beetles in field corn. The problems encountered with seed-treated plants in northern Missouri soybean and corn fields are rare, but can occur when field conditions limit the efficacy of the insecticide seed treatments.