Cereals: Fall Armyworm

Excerpt from Agronomy Guide for Field Crops (Chapter 6)

Order OMAFRA Publication 811: Agronomy Guide for Field Crop

Table Of Contents

1. Description
2. Life History
3. Damage
4. Scouting Technique
5. Action Thresholds
6. Management Strategies
7. Updates on Cereals: Fall Armyworm
8. Related links...

Description

Full-grown fall armyworms are 4 cm (1^1/2in.) long, varying in colour from light tan or green to near-black. Three white, thin strips run down the back with one thicker, yellow band with red spots running along the side, just above the legs of the larvae. The fall armyworm larvae has a white inverted "Y" on the front of the head, while the true armyworm does not. The fall armyworm head is dark brown.

Plate 19. Fall armyworm larva damage on corn ear. Larvae leave entry holes on the exterior of ear. Note head is black with a white, inverted "Y" on the front.

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Life History

Fall armyworm adult moths migrate from the southern states and show up later in the season when the corn is fully grown. This insect cannot overwinter in areas where the ground freezes.

Damage

Fall armyworms attack seedling wheat in the fall from September until frost. Fall armyworm feeding occurs in the daytime, unlike true armyworm feeding, which occurs at night. Initial leaf feeding appears as ragged-edged holes and moist, reddish-brown frass can be found nearby.

Scouting Technique

Examine 20 plants from five locations in your field to determine the level of infestation. Record the size and number of larvae. When scouting, check the backs of armyworms for parasite eggs. These small, oval, yellowish eggs are usually located just behind the head of the larva. These are eggs of a parasitic fly whose maggots will kill the armyworm larvae.

Action Thresholds

Two to three unparasitized larvae, less than 4 cm (1^1/2 in.) in length, per square foot.

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Management Strategies

Fall armyworm populations are rarely common in winter cereals. If the action threshold is reached, a spray may be necessary. See OMAFRA Publication 812, Field Crop Protection Guide, for insecticide recommendations. (Order OMAFRA Publication 812)

Updates on Cereals: Fall Armyworm

• Field Crop Protection Guide - Publication 812
  • Cereals: Armyworm (True and Fall)

Related links...

• Insects
• Cereals

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