Scouting for Fall Armyworm
Pest Importance
- Fall armyworm, Spodoptera frugiperda, is a minor pest of corn in the United States.
- Economic damage is sporadic from year to year.
- Fields at highest risk from injury are:
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- Fields planted to non-Bt hybrids without Lepidoptera control
- Fields in the southern U.S. and Texas
- Late-planted fields
- Late-maturing hybrids
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| Early stage fall armyworm larva |
Injury Symptoms in Whorl-Stage Corn
- Early stage larval feeding:
- Causes “windowpane” and shot holes in leaves
- Late-stage larval feeding:
- Causes elongate, ragged holes (see photo below)
- May cut leaves in half
- Injures developing tassel in VT stage
- Plugs whorl with wet, yellowish-brown frass
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| Whorl-stage corn injury from fall armyworm |
Scouting for Fall Armyworm
- Only larvae in whorl-stage corn can be controlled with insecticides; larvae in corn ears are protected
- Scout for larvae in whorl-stage corn:
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- Select 20 consecutive plants in a row.
- Inspect plants for feeding injury.
- Confirm identity of pest species as fall armyworm.
- Repeat 20-plant sample at 4 additional locations.
- Determine percent infestations based on 100 plants.
- Consider insecticide application when 20% of whorl-stage plants are infested with live larvae.
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Identification of Fall Armyworm
Dark spots (tubercles) on dorsal surface arranged in "trapezoid" or when near the tail, in a "square" pattern. Spots are darkened in photo for emphasis.
Fall armyworms can be distinguished from similar corn caterpillars by 2 physical characteristics:
- Inverted “Y” pattern on the front of a dark head (see next 2 photos)
- Dark spots (tubercles) on dorsal surface arranged in “square” or “trapezoid” pattern (see third photo)
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Similar caterpillar species found on corn (left-right): armyworm, fall armyworm
and corn earworm. The fall armyworm has an inverted "Y" pattern on the front of a dark head. |
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| An inverted "Y" pattern on the front of a dark head identifies the fall armyworm. |
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Dark spots (tubercles) on dorsal surface arranged in "trapezoid" or when
near the tail, in a "square" pattern. Spots are darkened in photo for emphasis. |
Photos and Text
Marlin E. Rice; Reviewed by Susan Moser, Herb Eichenseer and Laura Higgins
Reference
Bessin, Ric. 2003. Fall armyworm in corn. University of Kentucky Cooperative Extension Service. ENTFACT-110.
