A l A b A m A A & m A n d A u b u r n u niversities M a n a g e M e n t O f Fall Armyworm ANR-1019 in Pastures and Hayfields he fall armyworm, Spodoptera Behavior Patterns Another reason for the sudden Tfrugiperda, is a chronic pest appearance of this insect is that in the southeast. the caterpillars the fall armyworm is in the same insect family the larger fall armyworms will feed on a variety of forage crops, sometimes “march into” (quickly but seem to prefer lush, green, (Noctuidae) as cutworms and other armyworms. Fall army- invade) an uninfested area in well-fertilized bermudagrass. search of food once an adjacent Other forage grasses which are worm caterpillars damage grass by chewing plant tissue. field has been defoliated.l arge hosts for fall armyworm are armyworms frequently disap- Fall armyworms are typically bahiagrass, pearl millet, sorghum- pear almost as suddenly as they most active early in the morning, sudan hybrids, tall fescue, and appeared, either burrowing into late in the afternoon or in early various winter annuals including the ground to pupate or moving evening, but on taller, unmowed ryegrass, rye, wheat, and oats. on in search of food. more than 60 plants have been grass, they can be observed reported as hosts of the fall feeding on foliage throughout the armyworm, including corn, alfalfa, day. On closely grazed or recently Damage cotton, soybeans, and most mowed hayfields, fall armyworm Fall armyworm damage may vegetable crops. larvae spend the warmer hours of vary in appearance and severity the day deep in the sod. according to the type of grass and Seasonal Occurrence Fall armyworm damage often management practices. in closely seems to appear “overnight.” grazed fields, the grass may seem As the name indicates, fall Young armyworms don’t eat much. to thin out and develop brown armyworms are most numerous Almost all the damage is caused spots similar to those sometimes in late summer or early fall. by the oldest caterpillars which eat seen on golf courses (see Figure usually, reports of fall armyworm more than all the other ages put 2). these spots look burned or damage begin to come in during together (see Figure 1). therefore, browned out. this appearance is late July or early August. First an infestation may have been the result of grass plants rapidly reports are usually from southern present but not detected because dehydrating after fall armyworm Alabama. there are three or of the small size of the caterpillars. larvae have chewed off the tender more generations of fall army- worm each year. Occasionally, severe outbreaks occur as early as mid-April. 6th (last molt) Fall armyworms are suscep- tible to cold, and are unable to survive even the mildest winters in Alabama. each year, fall armyworm moths, carried by air currents, make their way from southern Florida and Central 5th and south America. the size and timing of the initial moth flights are two factors that influence the 4th rd outbreak potential of this pest. nd 3 st 2 droughty conditions are 1 favorable for the fall armyworm. Figure 1. Relative amounts of food eaten by a fall armyworm caterpillar during each growth stage. www.aces.edu darken and noticeable stripes appear. When fully grown, larvae may be up to 11⁄2 inches long and vary in color from light green to almost black with several stripes along the body (see Figure 4). the “face” is marked with a light- colored inverted “Y.” Just behind the head, on the back of the cater- pillar, you will see three thin white stripes running the length of the next segment. sometimes these lines extend along the length of Figure 2. Fall armyworm damage on closely mowed grass. Note brown patches resembling the caterpillar, as seen in Figure 4. drought damage. there are usually small dark spots on the top side of each segment foliage. For this reason, fall army- fescue, or orchardgrass can be of the body. On the next-to-last worm damage often resembles an even more serious situation. segment, these spots are arranged drought damage. seedlings of these fall-seeded like the corner points of a square plants are small when popula- in hayfields or in pastures (see Figure 5). where there has been substantial tions of fall armyworm are at Pupae. development from growth accumulation, virtually all seasonal highs. these crops can egg to fully grown larva requires tender green material may be severely stunted or killed about 2 to 3 weeks. At this point, be removed, leaving only if fall armyworms feed too far larvae burrow into the soil and tough stems a few inches long down on these plants. form pupae. the moths emerge protruding from the soil surface in about 10 to 14 days. (see Figure 3). brown patches Description appear in the field and can rapidly increase in size. and Life Cycle Management Tips established, healthy, bermuda- adult. the adult fall army- for Perennial Grass grass is rarely killed by fall worm is an ash-gray moth with 1 Pastures and Hayfields armyworms, but the complete a wing-span of about 1 ⁄2 inches. defoliation caused by a severe the front wings are mottled and Fall armyworm damage is infestation weakens plants and have white or light gray spots most likely to occur from August deprives livestock of pasture or a near the tips. the back wings through October when popula- hay producer of a hay cutting. are white with a narrow, smoky- tions are at seasonal highs. during brown edge. moths become periods of drought, it is not Fall armyworm damage active at twilight and feed on uncommon to receive the first on newly established grasses nectar. they have an average life reports of damage in July. natural including winter annuals, tall span of 2 to 3 weeks. enemies of the armyworm are less eggs. the female moths lay effective during drought years. eggs at night in masses of up to damage from armyworms several hundred on light-colored seems to come in “waves,” about surfaces, such as fence rails, tree a month apart. this is because trunks, and the underside of tree moth activity and egg laying limbs. the eggs are light gray peak periodically even though and covered with grayish fuzz there is substantial overlap from the female’s body. these between generations. Fields masses darken with age, and the damaged by fall armyworm eggs hatch within 2 to 4 days. All should be closely monitored the eggs within a mass hatch at for the rest of the season to about the same time. determine whether further treat- Larvae (caterpillars). the ment is required. two weeks tiny, light-colored, black-headed after damage has occurred, start Figure 3. Fall armyworm damage in a hay- larvae spin down to the ground checking for small caterpillars. field. Caterpillars have eaten the tender, green portions of the grass, leaving jagged on silken webs and begin to leaf edges and tough leaf bases. feed. As they grow, their bodies 2 the Alabama Cooperative extension system treatment threshold. the decision to treat for fall army- worms depends on the stage of the armyworms and the intended use of the forage. A population of 3 or more fall armyworms per square foot is a ➡ reasonable treatment threshold. As with other pests, timing is important. if infestations are detected too late, the damage may already have been done. if necessary, treat with insec- ticides at the right time. small Figure 4. Fully grown fall armyworm larva. Note inverted “Y” on the head capsule and fall armyworms are much easier the three white stripes just behind the head. to kill than larger ones. some products will not control large larvae at all. if you check an area properly, you can determine the extent of an infestation, and spot-treat. ➡ Frequently, mowing is the best option for salvaging a hay crop. When this approach is taken it may be possible to avoid using an insecticide. Insecticidal Control. if control is necessary on perennial grass pastures and hayfields, numerous insecticides may be effective (see table 1). Pay close Figure 5. Fully grown fall armyworm larva. Note set of four dots on the end of the abdomen. attention to grazing and harvest restrictions. note that methomyl because moths prefer light- Closely examine areas where is registered for use only on colored surfaces on which to lay birds are congregating. bermudagrass. eggs, check these first.i n pastures in established pastures or • Apply insecticides early and hayfields, fence rails, fence hayfields, check in and around or late in the day, because fall posts, and tree limbs are favored areas with dead grass or where armyworm larvae are most active egg-laying sites. birds are congregating. if no at these times. if a hayfield has been heavily caterpillars are seen on the grass, • Apply sprays by ground damaged, fertilize as recom- look in the thatch at the base of in a minimum of 30 to 40 gallons mended to allow for another hay the plants for larvae and green of water per acre, or by air in crop. badly damaged pastures pellets of frass (larval excrement) a minimum of 3 to 5 gallons of may need to be “rested.” if about the size of bahiagrass water per acre. Control of larvae possible, restrict grazing on badly seeds. if available, use an insect longer than 3⁄4 inch may be damaged pastures until the net to “sweep” the grass in early poor. Control of larvae in tall or grass has regrown.