Corn with Insect Trait Protection
Fall armyworm (FAW) larvae can damage corn at various stages of development by feeding on leaf or ear tissues. FAW
larvae are smooth skinned, vary in colour from light tan to dark green or black, with three yellow stripes and a dark
stripe down the back. There is an equally wide, wavy, yellow stripe, splotched with red next to the dark stripe. Early
instar larvae are dark green with black heads and usually found in groups on the plant. Larvae have four pairs of
abdominal prolegs and a pair of anal prolegs at the end of the body.1 Full-grown larvae are about 4 cm (1.5 inches)
Larvae of FAW, true armyworm (TAW), corn earworm (CEW), western bean cutworm (WBC), European corn borer (ECB), and
southwestern corn borer (SWCB) can be mistaken for each other. Correct identification can affect management decisions.
To differentiate FAW larvae from other species, look at the head of the larva.
- Fall armyworm larvae heads have a prominent white, inverted Y-shaped mark between the eyes. The FAW larvae vary from
light tan or green to almost black.
- True armyworm larvae have a grey or greenish-brown head covered with a network of lines.
- Corn earworm larvae usually have an orange head with no ‘Y’ mark. CEW larvae vary in colour ranging from light green
or pink to dark brown or nearly black. Early instars are nearly translucent light green and solitary. Bodies have
alternating light and dark stripes running the length of the body and double dark stripes down the centre of the back.
The body is covered by regularly occurring tubercles with two or three stiff black hairs.
- Western bean cutworm larvae are tan with a darker, faint diamond-shaped pattern on their back, and dark stripes
immediately behind their head.
- Southwestern corn borer larvae are dull white with a pattern of raised black spots on the body.
- European corn borer larvae have smooth, dirty white coloured skin, often having a pinkish tinge, with numerous dark
spots scattered over the sides and top of the body. The head is dark brown to black.
European Corn Borer
Western Bean Cutworm
Southwestern Corn Borer
Fall armyworm cannot overwinter where the ground freezes. FAW moths migrate north during the growing season from
overwintering sites in South Texas/Northern Mexico and South Florida.3,4 Adult moths lay masses of 50 to 150 spherical,
grey eggs on leaves.1 Life cycle is dependent on temperatures, and larvae hatch after a week and initially move into the
whorl to feed.5 One generation of FAW requires about 30 days to develop.3
Vegetative Damage Symptoms
Late-planted fields in whorl stage are targeted by adult moths for egg laying sites. Young FAW larvae remove the top
layer of the leaf and eat through leaves, causing small pin holes. Larvae continue to feed in the whorl, causing leaves
to have a ragged appearance as they unfurl from the whorl (Figure 2). FAW actively feed during the day, particularly
early in the morning and late afternoon, consuming large amounts of leaf tissue. Larvae can be found deep in the whorl,
often protected by yellowish-brown frass.
Figure 2. Severe fall armyworm feeding damage.
Larval Ear Feeding Damage6
Fall armyworm larvae feed by burrowing through the husk on the side of the ear, unlike corn earworm. Larvae also enter
at the base of the ear, feeding along the sides and may tunnel into the cob. They usually emerge at the base of the ear,
leaving round holes in the husks. Fall armyworm larvae can infest corn from tasseling to the dough stage of growth.
Larvae feed on tassels, immature ears, ear shanks, and tunnel into stalks. Heavy infestations of larvae feeding on
kernels may result in yield losses. Yield losses may also occur from ear drop and lodging caused by larval feeding
damage in ear shanks and stalks.4
Leaf damage increases and yield potential decreases as more plants are found with egg masses.7 However, scouting for FAW
can be difficult. Early FAW damage appears as “window paning” and small holes in leaves. Damage from larger larvae
results in ragged leaves. As corn ears develop, FAW larvae migrate from the whorls to the ears and damage kernels. If
whorl damage exists, scout 20 consecutive plants in 5 locations of a field.1,2,3,5 Pull some whorls and unroll the
leaves to make larval counts. Begin scouting efforts when corn is near tasseling and silking stages. Look for large
larvae in emerging tassels and very small ears. Continue to check closely until silks begin to turn brown.
If the corn crop does not have B.t. traits (Cry1F) offering control against FAW, an insecticide application may be
considered. However, the use of insecticides should only be used once the economic threshold has been met. Economic
thresholds vary across regions and are dependent on crop stress levels. Control can be considered when 50% of plants
have live larvae (without parasite eggs) smaller than 2.5 cm (1 inch) are present.5 Consult your local agronomists for
economic thresholds in your area. Parasites and beneficial insects can help keep fall armyworm from reaching problematic
levels. Look for signs of small white parasite fly eggs laid behind the heads of larvae before deciding to apply an
Insecticides should be applied before FAW larvae become larger than about 3 cm (1.25 inches) and burrow deep into the
whorl or enter ears of more mature plants.2 Insecticides may not be effective if the larvae are burrowed in the whorl
because the frass can block the FAW feeding tunnel. High pressure (280 Litres per hectare or 30 gallons per acre) should
be used with ground rig applications of pesticides.1
Fall armyworm has been known to cost farmers hundreds of millions of dollars from corn loss annually.7 Traited corn
products with protection against FAW can help reduce loss. However, it is important to determine which insect is causing
feeding damage to move forward with management this year and in the following corn crop.
1 Bessin, R. 2019. Fall armyworm in corn. University of Kentucky – Lexington. Entfact-110.
2 2009. Fall armyworm Spodoptera frugiperda Smith. Purdue University. https://extension.entm.purdue.edu/fieldcropsipm/insects/fall-armyworm.php.
3 Capinera, J.L. 2020. Fall armyworm featured creatures. University of Florida. https://entnemdept.ufl.edu/creatures/field/fall_armyworm.htm
4 Porter, P., Cronholm, G.B., Parker, R.D., Troxclair, N., Patrick, C.D., Morrison, P., and Archer, T.L. 2002. Managing
insect and mite pests of Texas Corn. Texas A&M University System. B-1366.
5 Ontario Ministry of Agriculture, Food, and Rural Affairs. 2021. 15. Insects and pests of field crops. Agronomy Guide for
Field Crops. Pub 811.
6 Estes, K. 2016. Corn earworm, European corn borer, fall armyworm, or western bean cutworm: Which one is causing the
injury I’m finding on my corn ears? University of Illinois at Urbana-Champaign. https://farmdoc.illinois.edu/field-crop-production/uncategorized/corn-earworm-european-corn-borer-fall-armyworm-or-western-bean-cutworm-which-one-is-causing-the-injury-im-finding-on-my-corn-ears.html.
7 Cruz, I. and Turpin, F.T. 1983. Yield impact of larval infestations of the fall armyworm (Lepidoptera: Noctuidae) to
midwhorl growth stage of corn. Journal of Economic Entomology. Vol. 76. Pages 1052-1054.
Web sources verified 07/16/2021.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary from location to location and from year to year,
as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years
whenever possible and should consider the impacts of these conditions on the grower’s fields.
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