Insect I.D.: July 2001, TURF-DAMAGING CATERPILLARS: A Few Words About Worms

The black cutworm, armyworm and fall armyworm are native to North America but they have been spread worldwide by accidental introductions. The black cutworm and fall armyworm are actually tropical and semitropical species that fly from the Gulf States to cool-season turf areas each spring. The armyworm and bronzed, variegated and glassy cutworms can survive northern winters.

All species of turfgrasses are hosts to these larvae. Black cutworms and fall armyworms most commonly damage the short cut turf found on golf course greens and tees.

The adults are dull brown and gray colored moths with wingspans of 1 3/8 to 1¾ -inch (35 to 45 mm). At rest, the wings are folded flat over the abdomen.

LARVAE. The larvae generally have hairless bodies except for a few scattered bristles. Besides the three pairs of true legs, these larvae have five pairs of fleshy prolegs on the underside of the abdomen. Most cutworms have characteristic markings on the head and body that aid in species identification. Full-grown cutworm and armyworm larvae are 3/16-inch (6.0 mm) wide and 1¼ to 2 inches (32 to 50 mm) long. Most cutworms and the armyworm coil into a spiral when disturbed.

Cutworms are named as such because of their nocturnal feeding habit of cutting off plants close to the ground. On golf course greens and tees, black cutworms and fall armyworms graze on the grass blades of short cut turf, causing circular or finger-shaped sunken areas, similar to ball marks. Armyworms feed on grasses any time of the day and are known for their habit of moving and feeding, en masse, from one turfgrass area to another. They commonly eat everything green, leaving only a few stems. Bronzed cutworms occasionally damage cool-season turf under the cover of snow. Other species of cutworms are relatively uncommon and their damage is minor.

DETECTION & MONITORING. Regular monitoring of turf for evidence of cutworm or armyworm infestations and applying treatment only when larvae are present and/or damage seems eminent, are keys to control. Monitoring includes looking for larvae, damage and/or evidence of birds (starlings) probing the turf for larvae.

To determine if larvae are present, an use a flushing solution of liquid soap and water (two tablespoons of liquid Joy® dishwashing detergent in two gallons of water) spread over a 1-square-yard area to flush larvae to the surface. In our experience, this solution has not damaged turf.