Field Corn

Fall Armyworm

Frank B. Peairs

Armyworm

Identification (and life cycle/seasonal history)

Adults are about one inch long, with dark and light gray forewings mottled with light and dark

spots. The hind wings are grayish to pinkish-white. Fall armyworm larvae have a white inverted Y-shaped mark on the front of their dark head. They are smooth skinned and vary in color from light tan or green to nearly black, with three yellowish-white hairlines down the back. There is a wider dark stripe and a wavy yellow-red stripe on each side. The larval stage lasts from three to four weeks. Fully developed larvae are about 38 millimeters (1? inches) long. Unlike armyworms, fall armyworms feed during the day and night, but are usually most active in the morning or late afternoon.

Plant Response and Damage

Small holes and "window pane" feeding characterize early larval feeding on corn leaves and in the whorl. They may enter the ear and feed on new kernels. Larger larvae may be found deep within the whorl often below a "plug" of yellowish-brown frass. Fall armyworm will feed on corn plants in nearly all stages of development, however it prefers later plantings which have not yet silked.

Management Approaches

Resistant Varieties

Control can be expected with Bt corn hybrids containing the Herculex I event. See Managing Corn Pests with Bt Corn, http://www.ext.colostate.edu/pubs/crops/00708.html, for details on the use of Bt corn hybrids to control corn pests.

Chemical Control

Product list for Fall Armyworm:
Pesticide	Product/Acre (Fl oz. or oz. product)	Preharvest Interval, remarks
Asana XLR,1	5.8 - 9.6	21 days. Apply as necessary to maintain control. Extremely Hazardous to Bees!
Baythroid XLR,1	2.8	21 days. See label. Extremely Hazardous to Bees!
bifenthrin 2ER1,2	2.1 - 6.4	30 days. Use rates below 5.12 fl. oz. only if spider mites are NOT a concern. Extremely Hazardous to Bees!
carbaryl1,2	See labels	48 days grain or stover, 14 days silage. Extremely Hazardous to Bees!
chlorpyrifos 4ER1,2	16 - 32	35 days. 14 days grazing. Not for use on popcorn. Extremely Hazardous to Bees!
CobaltR1	13 – 26	21 days. 14 days graze. Not for use on popcorn. Extremely Hazardous to Bees!
Delta Gold R,1	1.5 - 1.9	21 days to harvest grain or fodder. 12 days to forage. Do not apply more than 0.095 lb ai/acre/crop. Extremely Hazardous to Bees!
HeroR,1	4.0 - 10.3	30 days to harvest grain or fodder. 60 days to forage. Do not apply more than 0.4 lb ai/acre/crop. Extremely Hazardous to Bees!
permethirnR,1,2	See labels	30 days. Liquids are Extremely Hazardous to Bees!
Mustang MAX ECR,1	3.2 - 4.0	30 days grain or stover, 60 days silage. Extremely Hazardous to Bees!
ProaxisR,1,2	2.56 - 3.84	21 days. Apply as required by scouting or locally prescribed corn growth stages. Do not apply more than 0.06 lb (AI)/acre/season. Extremely Hazardous to Bees!
Radiant SC	3 – 6	28 days. 3 days fodder or forage.
Tracer1	1 - 3	28 days grain or stover, 7 days silage.
RRestricted use pesticide. 1Labeled for chemigation. 2Generic active ingredient, may be additional formulations.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

Categories: Field corn, Insects, Fall armyworm

Date: 5/16/2008