Forages: Armyworm (True - Pseudaletia unipuncta, Fall - Spodoptera frugiperda)Pub 812: Field Crop Protection Guide > Chapter 3: Forages > Armyworm (True and Fall) Field Crop Protection Guide 2011-2012, Order 2011-2012 publication Table of Contents
DescriptionTrue armyworms, full grown, are 4-cm (1 1/2-in.) dull-green to brown larvae that can be easily confused with other caterpillars, including variegated cutworm and fall armyworm. Two distinguishing features that true armyworm possess are white-bordered stripes running laterally along the body and dark diagonal bands at the top of each abdominal proleg. The head is yellow-brown with a network of dark brown lines creating a pattern. The adult sand-coloured moth has distinctive white spots on the centre of each forewing. 
Image 1. True armyworm larvae have black bands at the top of each proleg and the lighter brown head. Full-grown fall armyworms are 4 cm (1 1/2 in.) long, varying in colour from light tan or green to near-black. Three white, thin stripes run down the back with one thicker, yellow band with red spots running along the side, just above the legs of the larvae. Scattered along the body are black spots called tubercles that have spines coming from them.
Integrated Pest Management OptionsControl is warranted when 5 or more larvae (smaller than 2.5 cm) per 30 cm x 30 cm (square foot) are found. Avoid treating with insecticides when large numbers of parasitized larvae are present. In seedling crops, two or three larvae (smaller than 2.5 cm) per 30 cm x 30 cm may warrant control. If larvae have white eggs attached to them, they are parasitized and may not need treatment. If the larvae are almost full grown (2.5 cm or larger), there is no benefit in applying insecticide since most of the feeding damage has already been done.
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