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F@stSheet Ent-2002

Armyworms IN THIS F@STSHEET BIOLOGY DAMAGE CONTROL FOR MORE INFORMATION

        Armyworm outbreaks are difficult to predict but infestations seem to occur in portions of the state every year especially after rains in the early fall. Common species of armyworms present in Texas include: the fall armyworm, Spodoptera frugiperda (J.E. Smith); the yellowstriped armyworm, Spodoptera ornithogalli (Guenee); the beet armyworm, Spodoptera exigua (Hubner); and the armyworm, Pseudaletia unipuncta (Haworth). The fall armyworm is the insect that usually causes the most problems in pastures, small grains, golf courses and home landscapes.

BIOLOGY
      The fall armyworm has four life stages: egg, larva, pupa and adult. The fall armyworm has not shown the ability to diapause so its ability to survive winter depends on the severity of the temperature. The fall armyworm does overwinter in the southern regions of Texas in the pupal stage. The adult is a moth that migrates northward as temperatures increase in the spring. The adult moth has a wingspan of about 1.5 in. The hind wings are white; the front wings are dark gray, mottled with lighter and darker splotched. Each forewing has a noticeable whitish spot near the extreme tip.
        Eggs are very small, white laid in clusters of 50 or more and are covered with grayish, fuzzy scales from the body of the female moth. The eggs are seldom seen and are laid at the base of appropriate host plants.
        Larvae hatch from the eggs and when full-crown larvae are green, brown, or black and about 1 to 1.5 in. long when full grown. The larva has a dark head capsule usually marked with a pale, but distinct, inverted "Y." Along each side of its body is a longitudinal, black stripe, and along the middle of its back is a wider, yellowish-gray stripe with four black dots on each segment. The larvae have five stages or instars and usually hide in debris on the soil surface in the middle of the day. When full grown, larvae will enter the soil and form the pupal stage. Adult moths emerge from pupae. Moths mate and lay eggs, thus starting the life cycle over again. Lush plant growth is preferred by the adults for egg laying.
        Several generations (A generation is the development from egg to adult stage.) occur each year and typically the life cycle from egg to adult takes 28 days. The life cycle can be extended if cooler temperatures occur and can last up to several months. Armyworms in the spring and summer occur in more distinct groups than later in the season. Fall populations of larvae often blend together several generations and may appear to be continually occurring.

DAMAGE
        When feeding, larvae strip foliage and then move to the next available food. High populations appear to march side by side to the new food. Thus, the name armyworms has been applied.
        Armyworms attack many different kinds of plants. When food is scarce, they will move to plants that are not normally attacked. Thus, armyworms can be found on nearly any plant as they migrate in search of edible foliage. Plants attacked by armyworms include: bermudagrass, grain and forage sorghum, corn, small grains, sweet potato, beans, turnip, clover, tobacco, spinach, cucumber, potatoes, tomatoes, cowpeas, cabbage and bluegrass.
        Damage consists of foliage consumption. The small larvae will chew the green layer from the leaves and leave a clearing or "window pane" effect. The first three instars do very little feeding while the last two instars consume 85% of the total foliage consumed.

CONTROL
        Armyworms should be controlled when they occur in large numbers or plant damage is becoming excessive. The fall armyworm attacks grain in the fall in the seedling stage; therefore, a relatively small number of larvae per square foot can do heavy damage. Preventive treatments normally are not justified because attacks are sporadic and egg mortality is usually high. During favorable seasons, a number of parasitic enemies keep fall armyworm larvae down to moderate numbers. Early detection works best and is achieved by frequent, thorough inspection of plants. Outbreaks seem to occur shortly after a rain or supplemental irrigation.
        Fall armyworms feed any time of the day or night, but are most active early in the morning or late in the evening. Susceptible fields or lawns should be scouted by counting the number of armyworms in a square foot area in 8 different sites. Divide the total worm count by 8 to find the average number of armyworms per square foot. Be sure to take samples in the interior of the field because this pest is often heaviest near the field margins. Sometimes, only the field margins require treatment.
        The threshold level ranges from two to three larvae per square foot for seedling wheat. For older plants, three to four larvae and obvious foliage loss justify control measures. Thresholds in improved pastures and lawns vary with conditions but treatment should be considered when counts average three or more small worms per square foot.
        Insecticide choices vary with the crop but possible choices in pastures (with grazing restrictions in parentheses) include carbaryl (Sevin®) (14 days), malathion (0 days), methomyl (Lannate®) (7 days), methyl parathion (Penncap®-M) (15 days) and various biologicals such as Dipel®(0 days). Insecticide choices in lawns and turf include halofenozide (Mach® 2), isofenphos (Oftanol®), chlorpyrifos (Dursban®), bifenthrin (Talstar®), carbaryl (Sevin(&) and diazinon.

FOR MORE INFORMATION
        For more information about armyworms refer to Extension fact sheet B-1220, Managing Insect and Mite Pests of Texas Sorghum; B-1251, Managing Insect and Mite Pests of Small Grains; B-1401, Integrated Pest Management Guide for Texas Forage Crops; and L-1725, Armyworms in Texas Landscapes.  These publications, and help with additional questions about armyworms or other pest problems, can be obtained by contacting your local county Extension office.

Authors:
Authors: James Robinson, Chris Sansone, John Jackman, Extension Entomologists, Texas Agricultural Extension Service

Publication information:
This publication is part of the House & Landscape Pest Series produced by the Department of Entomology, Texas A&M University, College Station, TX 77843-2475. The most recent update can be found at: http://dallas.tamu.edu/insects/FastSheets/Ent-2002.html . Series Editor: M. Merchant. For more information about arthropods, check out the Texas A&M Entomology Website at http://insects.tamu.edu/
Last revision: 10/9/01