Fall armyworm outbreaks are occurrring this week in hayfields, pastures, and home lawns across southern and western Kentucky. This follows a large moth flight detected in the trap catch at the UKREC in Princeton. Trap catches so far in Lexington have been very low. This insect feeds primarily on grasses -– bermudagrass, wheat, and ryegrass but will attack many other crops. Fall armyworms spend about 3 weeks as caterpillars but 80% of their feeding occurs in the last few days of their development. While devestating damage appears overnight, the worms have been present for some time before reaching their prime eating stage.
The key to preventing significant losses to fall armyworm is early detection of infestations. Good control can be acheived and losses reduced if infestations are found while fall armyworms are small (3/4 inch long or less). Full-grown worms are about 1.5 inches long. At this size they have done most of their damage and also are harder to kill. Examine brown patches in field or turf for chewed leaves, the earliest signs of an infestation, or small particles of dark green to black waste. These caterpillars are up feeding on leaves during the evening or on cloudy days but hide under surface residue or in soil cracks during the day. During the day, check under surface residue and in soil cracks for hiding armyworms. An average of 2 to 3 per square foot may justify treatment.
Fall armyworms move northward into Kentucky every year but usually cause only scatterd problems in late-planted corn or fall-seed forages. Late summer outbreaks are favored by rainy periods that increase the survival rate of small larvae. This insect can be active until a killing frost so stay alert for expanding brown areas in stands and follow the trap catch information from Princeton in the Kentucky Pest News.
S-225 Ag Science North
Lexington, KY 40546-0091
Phone: (859) 257-5955
Fax: (859) 323-1120
*Western Ky Research & Education Center
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