Fall armyworm can be one of the more difficult insect pests to control in corn. Late planted fields and later maturing hybrids are more likely to become infested. Fall armyworm causes serious leaf feeding damage as well as direct injury to the ear. While fall armyworms can damage corn plants in nearly all stages of development, it will concentrate on later plantings that have not yet silked. Like European corn borer, fall armyworm can only be effectively controlled while the larvae are small. Early detection and proper timing of an insecticide application are critical.
Each summer, adult moths move northward in progressive stages from overwinter sites along the gulf coastregion and begin to appear in late June or early July. The spherical gray eggs are laid in clusters 50 to 150, usually on the leaves. Egg masses are covered with a coating of moth scales or fine bristles. Larvae hatch in 3 to 5 days and move to the whorl.
Fall armyworm vary from light tan to black with three light yellow stripes down the back. There is a wider dark stripe and a wavy yellow-red blotched stripe on each side. Larvae have four pairs of fleshy abdominal prolegs in addition to the pair at the end of the body. Fall armyworm resembles both armyworm and corn earworm, but fall armyworm has a white inverted "Y" mark on the front of the dark head. The corn earworm has a orange-brown head, while the armyworm has a brown head with dark honeycombed markings. Fall armyworm has four dark spots arranged in a square on top of the eighth abdominal segment.
Very early symptoms of fall armyworm resemble European corn borer infestation. Small holes and "window pane" feeding in the leaves emerging from the whorl are common. Although initial symptoms of damage are
similar, thresholds and control measures differ. Therefore it is important to find the live larvae and determine which insect is causing the damage. Unlike armyworm, fall armyworm feeds during the day and night, but are
usually most active in the morning or late afternoon. The most common damage is to late pretassel corn. Larger fall armyworm larvae consume large amounts of leaf tissue resulting in a ragged appearance to the leaves similar to grasshopper damage. Larger larvae are usually found deep in the whorl often below a "plug" of yellowish brown frass. Beneath this plug, larvae are protected somewhat from insecticide applications. Plants often recover from whorl damage without any reduction in yield. Larvae will also move to the ear as plants begin to tassel and young ears become available. The ear may be partly or totally destroyed. Damage to the ear renders the ear unmarketable.
Biological: In favorable seasons, a number of parasitic enemies keep the fall armyworm caterpillars down to moderate numbers. The most effective include the tachinids, Winthemia rufopicta and W. quadripustulata, the
brachonids, Apanteles marginiventris, Chelonus insularis and Meteorus laphygmae and Trichogramma spp. As is generally the case, however, cold, wet springs check the parasites more than they do the insects that they feed seasons, especially, watch should be kept of grassy fields for the appearance of the young worms.
Cultural: None available.
Monitoring: Corn growers should pay close attention to late planted fields or fields with a history of these problems. Problems are usually associated fields planted after June 1 to June 15. Early detection of infestations
will allow for more effective control of this pest. If present in damaging numbers in the field, it must be controlled while the larvae are still small. Finding an infestation after it is too late to obtain good control is a
serious and common problem. Because fall armyworm prefers whorl stage corn, late planted fields at this stage should be given a high priority when scouting. Begin checking corn in mid-June for fall armyworm activity. Survey 20 consecutive plants (selecting the first randomly) from at least 5 locations in the field. Small larvae cause "window pane" damage to leaves similar to European corn borer. A few days before tasseling, look for large larvae in the whorls which will be pushed out when the tassels emerge. These larvae may attack young ears. Continue to check for this insect until silks begin to dry. Pheromone traps are also used to monitor this insect in sweet corn. Usually a serious pest only of sweet corn planted after June 1. Treat if more than 10% of the whorls are infested with live larvae.
During silking, pheromone traps for fall armyworm are available to monitor for moth activity and assist in determining the need for sprays and length of spray intervals. Fall armyworm trap catch information, as well as that from corn earworm and European corn borer, determine the need for and frequency of sprays will the silks are fresh. After silks have dried, no additional sprays are needed.
Ambush (permethrin)- Apply as a foliar treatment at 6.4 to 12.8 fl oz per acre to a limit of 76.8 lbs per acre per season.
Baythroid 2 (cyfluthrin)- Apply as a foliar treatment at 2.8 fl oz per acre to a limit of 10 applications per acre per season.
Bt-products (various products) - Apply as a foliar spray and reapply as necessary.
Lannate 90 SP (methomyl)- Apply as a foliar treatment at 1/4 to ½ lb per acre to a limit of 8 lb per acre.
Larvin 3.2 F (thiodicarb)- Apply as a foliar treatment at 20 to 30 fl oz per acre to a limit of 300 fl oz per acre per season.
Pounce 3.2 EC (permethrin)- Apply as a foliar treatment at 4 to 8 fl oz per acre to a limit of 48 oz per acre per season.
Warrior 1 EC (lambda-cyhalothrin)- Apply as a foliar treatment at 2.56 to 3.84 fl oz per acre to a limit of 3.84 pt per acre.