David Owens, Extension Entomologist, owensd@udel.edu
Sod/Pasture/Alfalfa
Scout sod, pasture, and alfalfa for fall armyworm. There have been a couple of reports this week from Virginia and from New York of fall armyworm stripping alfalfa. In grasses, caterpillars can be scouted for by using a 1 ft x 1 ft pvc frame and a jug of soapy water. Pour the water in the frame to flush worms out of the thatch. Treatment thresholds from southern states are 2 per square foot. Caterpillars can also be swept for to quickly determine if they are present; thresholds from LSU is 1 worm per sweep. Keep note of the size of the worm. Large worms that are 1.5” will be difficult to kill and are very close to pupating. There have been reports of lower pyrethroid efficacy than is typical, but it is not clear if this was because the producer targeted large worms. Insect growth regulators and Bt are most effective on small worms. If worms are medium or larger, consider diamides, indoxacarb, or premixes. As always, consult the product label to determine if it is an approved use and the proper rate.
Soybean
Continue scouting double crop beans for corn earworm and for defoliation. Earworm counts have trended down, I am optimistic that we are past earworm peak. Soybean looper has been present in low to moderate numbers in many Sussex fields, and as noted above, reports from other states indicate that armyworm are feeding on and defoliation beans. While scouting double crop bean fields for defoliation and for earworm, pay attention to stink bugs. Up until R6, thresholds are 5 bugs in 15 sweeps. Once we reach R6, thresholds begin increasing. Soybean at R7 are considered safe.