Fall armyworm in sweet corn
In sweet corn the young larvae feed deep in the whorl, leaving ragged, window-paned leaves and sawdust-like frass. Later they bore into the side or tip of the ear. Late-planted corn and later-maturing varieties are most at risk, because the moths arrive in midsummer. Bt only works on larvae that eat it, so it has to be in the whorl when the caterpillars first appear.
At a glance
- Damage
- Lawns browned in a moving front; ragged corn whorls full of frass
- Type
- Chewing
- Settings
- Garden, Field
- Threshold
- 15% of plants infested (UMass, sweet corn)
- Ally
- Bacillus thuringiensis kurstaki
- Rate
- Label rate. DiPel DF lists Spodoptera and gives 0.5–2 lb per acre on corn (cereal grains); not every home Bt names armyworms
How to confirm it
A striped caterpillar up to 1½ inches (4 cm) long with a pale upside-down Y on its dark head and four dark spots in a square on top of the eighth abdominal segment, near the rear end. In lawns, pour soapy water over the edge of the browning area and the caterpillars come to the surface within 10 minutes.
Identification, lifecycle, degree days and every control option are on the full Fall armyworm profile. Not sure it is this pest? Answer four questions about the damage.