Turf - Fall armyworms

Fall armyworm season will be coming in August. These pests can sometimes attack turf. The following is an article on fall armyworms.

Fall armyworm caterpillars, sometimes known for marching in large "armies", are potential turf pests in late summer and fall. Consuming all green above-ground plant parts, they are capable of killing or severely retarding the growth of grasses. During most seasons, parasitic enemies keep fall armyworm larvae down to moderate numbers. Cold, wet springs seem to reduce the effectiveness of these parasites and allow large fall armyworm populations to develop. Conversely, years such as 2002 with mild winters and dry summer allowed early and sustained periods of infestation.

The fall armyworm has a wide host range but prefers plants in the grass family. Most grasses, including Bermudagrass, fescue, ryegrass, bluegrass, Johnsongrass, timothy, corn, sorghum, Sudangrass, and small grain crops, are subject to infestation.

Biology

The mature green, brown, or black larva, 35 to 50 mm long, has a dark head usually marked with a pale, and a distinct, inverted "Y". Along each side of its body is a longitudinal, black stripe. There are four black dots on the dorsal side of each abdominal segment.

The moth has a wingspan about 38.5 mm. The hind wings are white and the front wings are dark gray, mottled with lighter and darker splotches. Each forewing has a noticeable whitish spot near the extreme tip. The minute light gray eggs are laid in clusters on any vegetation (shrubs and posts included) and are covered with grayish, fuzzy scales from the body of the female moth. The eggs become very dark just before hatching. The pupa, approximately 30 mm long, is originally reddish-brown and darkens to black as it matures.

Fall armyworms probably overwinter as pupae in the Gulf Coast region of this country. Egg-laying moths migrate northward throughout the spring and summer and arrive in Delaware during August. New moths may continue to appear into October. Each female lays about 1,000 eggs in masses of 50 to several hundred. Two to 10 days later the small larvae emerge, feed gregariously on the remains of the egg mass, then scatter in search of food. Unlike the nocturnal true armyworms, fall armyworms feed any time of the day or night, but are most active early in the morning or late in the evening. When abundant, these caterpillars eat all the food at hand and then crawl in great armies to adjoining fields. After feeding for 2 to 3 weeks, the larvae dig about 20 mm into the ground to pupate. Within 2 weeks, a new population of moths emerges and usually flies several miles before laying eggs. Several generations occur each year in Delaware. Newly installed sod is more attractive to FAW and more susceptible to damage. Turf symptoms can first appear on lawn edges, and around areas near lights.

Control

The fall armyworm is more difficult to control chemically than the true armyworm. Control of fall armyworms will be improved if you cut the turf prior to treating. A light irrigation prior to treatment may also help as will treating late in the day. Large fall armyworms are difficult to control. Don't expect 90% control. Pyrethroids will do a reasonable job as will Sevin (carbaryl) and even Orthene (acephate) against small worms. For professionals, products like Mach 2 and Scimitar will also control turf feeding caterpillars, but don't expect miracles, especially if they are allowed to feed and grow for a week or more before treating. In warm weather the caterpillar can go from egg to pupa in 2 weeks. If the worms are very large (inch and a half long) then they will go into the soil very soon to pupate and control efforts may be a ineffective. Timing is important and a repeat application may be necessary in some situations. On a lawn, threshold is about one larva per square foot of turf. Soap disclosure solutions can be helpful for determining larval infestations.

Information from North Carolina State University.