Armyworms
Striped caterpillars that feed in large groups at night and can strip a lawn, grass crop or vegetable bed in a matter of days.
Also known as: True armyworm, Army caterpillars
Symptoms and identification
Leaves and grass blades are chewed from the edges, and seedlings may be eaten to the ground. Caterpillars are green to brown with light and dark stripes along the sides, and they hide in soil, thatch or mulch in the daytime and move in groups at dusk.
Causes
Moths lay eggs in dense grass and weeds, often after cool, wet spring weather followed by warmth. Outbreaks appear suddenly and often move into gardens from nearby grassland or crops.
Organic treatment
Hand-pick caterpillars in the evening. Spray Bacillus thuringiensis (Bt) on young larvae, or spinosad products allowed for organic use, in the evening when they feed.
Prevention
Keep grass and weeds cut short around gardens, check lawns and seedlings at dusk, and protect young transplants with netting or collars. Natural enemies such as birds and parasitic wasps help control numbers.
Chemical treatment (use with care)
Use an insecticide labelled for armyworms on that crop or lawn, following the label. Treat small caterpillars, as big ones are harder to kill.