Time for concern: July through August. Tassel emergence to harvest.
Key characteristics: White domed-shaped eggs are laid in clusters of 20-200 on the upper surface of the top leaves. Eggs turn tan and then purple just prior to hatch. Young larvae are initially dark with black heads, but as larvae develop they become light tan to pinkish with subtle longitudinal stripes. Late instars reach 1.5 inches long and have two black rectangles behind their orange-colored head; cuticle is smooth (i.e., do not have tubercles, warts, or bumps). Western bean cutworm moths are primarily grayish-brown with a wing-span of approximately 1.5 inches. Moths have a white stripe at the front of the forewing with two cream-colored outlined shapes behind them. Only completes one generation per year.
|Scouting/thresholds||Scout fields that are in the late whorl or early tassel stage during the moth flight for egg masses and small larvae. Egg masses are most often found on the upper leaf surface near the tassel. The action threshold for processing sweet corn is 4% of plants infested with eggs or larvae. The action threshold for fresh market sweet corn is 1% of plants infested with eggs or larvae. Consult the Sweet Corn Pheromone Trap Network for flight activity to assist with times to scout fields.|
|Resistant varieties||Bt sweet corn varieties that have Vip3A protein are labeled for western bean cutworm control. Check information on the label. Hybrids with only the Cry1A, Cry1Ab, or Cry2Ab proteins do NOT have activity against western bean cutworm.|
|Cultural Control||Deep soil disturbance through tilling may cause mortality of overwintering western bean cutworms, but no studies have directly tested the impact on larval survival.|
|Natural enemies||Trichogramma ostriniae has been shown to parasitize eggs in sweet corn but has not been tested as a control strategy. Lady bird beetles, lacewings, damsel bugs and spiders will feed on eggs and larvae.|
|Pesticides||Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production|