Armyworm ( Pseudaletia unipuncta ) is a caterpillar that can cause damage to both cool and warm season turfgrasses through Europe, Northern Asia and into the Mediterranean Basin. The damaging stage of the insect is the larval (caterpillar) stage. The adult female moth can lay 500 egg cluster in a row on a leaf blade in one night! Each female can lay thousands of eggs. The eggs will hatch in a week. The females will also lay eggs on structures like flags, plexiglass pains, golf course hole signs, etc.
There are normally three generations of the larvae stage. The first occurs from May to mid-June but normally occurs on field crops. The next two generations that occur June and July is the most damaging to turf, but the third generation August and September is also damaging to turf. Damage to turf can occur rapidly. The caterpillars move in mass moving from one area to another migrating at night. Turf can literally disappear overnight.
Culturally, endophyte containing perennial ryegrass and tall fescue are resistant to common armyworm. On golf courses wiping down the flags or hole signs when egg masses are present may help reduce potential caterpillar populations. On athletic fields wiping structures may help reduce populations too.
Chemically, the principle of controlling grass eating caterpillars with insecticides is to apply the treatment to the turf and omit irrigation for 12 to 24 hours until the insect consumes the foliage and makes contact with the treated surfaces.