Fall armyworm
(Spodoptera frugiperda)

Overview

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The Lepidopteran pest Spodoptera frugiperda is commonly known as the Fall Armyworm. This species can cause serious damage through heavy feeding on leafs as well as the ears of corn crops. The S. frugiperda larvae can be extremely difficult to control and it is critical to scout early to lessen the likelihood of a full blown infestation. Early damage is defined by small holes and “small transparent window panes” due to the young larvae feeding in the leaves from the whorl. Fall armyworms feed both day and night, which differs from the common armyworm, which feeds only at night. This greatly helps differentiate the two species in the field.

Main description

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The fully developed fall armyworm larva is approximately 3 cm long and varies in colour from light tan or green to near black. The fall armyworm has a dark brown head and three white, thin stripes run down the back. It also has 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 emerging from them. The fall armyworm larvae can be un-mistakenly distinguished from the true armyworm by a white inverted "Y" on the front of the head of the fall armyworm. Feeding in forages usually occurs in late summer and early fall, when the grown larvae fall to the soil to pupate.

Scouting

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Scouting should involve the search for fall armyworm eggs. If egg masses are present on approximately 5% of the plants, or if there is the presence of the larvae or symptoms of fresh feeding in 20-25% of the plants sampled, then immediate control should be considered as necessary. Treatment must take place before larvae burrow deep into the whorl or before they enter the ears of mature plants. A preferential control should be given to the smaller larvae (2 to 3 stages of development) to prevent damage and protect the crop.