Evaluation of foliar-applied insecticides to control potato leafhoppers (Empoasca fabae Harris) and tarnished plant bugs (Lygus lineolaris Palisot) in alfalfa in Illinois, 2011

This trial was designed to assess the ability of a variety of insecticides (Cobalt, Mustang Max, Nufos, and Warrior II) to manage populations of potato leafhoppers and tarnished plant bugs in alfalfa. The experimental design was a randomized complete block with four replications of each insecticidal treatment. The plot size for each treatment was 400 sq. ft. The insecticides were applied during late July and densities of potato leafhoppers and tarnished plant bugs were assessed at 0, 7, 14, and 20 days after treatment (DAT). Insects were collected by using a 15-in. diameter sweep net. Following collection, the insects were bagged, labeled, and frozen. Due to generally low insect pressure, the population densities at the beginning of the trial for both potato leafhoppers and tarnished plant bugs were relatively low. Following the application of insecticides, the 14 DAT sampling date was the only date that had significant differences in  insect densities. The use of insecticides targeting these two pests did not result in a clear benefit when applied to the low initial densities observed in this trial. Our results emphasize the need for a scouting-based approach for applying insecticides to manage these pests of alfalfa.