|Scientific Name||Spodoptera frugiperda (J.E. Smith)|
|Common Names||English: Fall armyworm; German: Heerwurm; Spanish: Gusano cogollero|
The adult's wings are mottled gray-brown and span up to about 40 mm (1.57 inch).
The mature larva can be up to 50 mm (1.97 inch) long; it is light brown, green or nearly black (especially in the armyworm phase) and bears longitudinal stripes.
The caterpillars of this moth feed mainly on leaves, munching on their edges and making holes, giving them a ragged and torn appearance.
If the larvae are numerous, they can completely defoliate the plants. When they have exhausted their food source, they invade neighbouring vegetation - which may often be another crop - in large numbers („armyworm“), devouring almost all suitable plant material in their path.
Infestations often remain unnoticed at first, as the small larvae prefer feeding sites close to the ground. By far most of the damage, however, is caused by the last instar larvae, which consume more plant biomass than all of the other instars put together. This often makes attacks by fall armyworm seem very sudden.
In corn, the caterpillars feed deep in the whorl, often concealed under their own frass. While the leaves may be heavily damaged, the plant usually compensates for the loss. If the growing point is destroyed, however, „dead heart“ symptoms will appear. The larvae frequently feed on the immature kernels inside the developing ear. This generally causes greater injury than the leaf damage. In cotton, bolls are penetrated and hollowed out. Seedlings of grasses and small grains can be completely cut off at the base. In hayfields or pastures, symptoms of fall armyworm infestation often resemble the effects of drought. On vegetables such as pepper and tomato, buds and growing points may be destroyed; fruits will be pierced, which can cause them to fall off or to rot.
Spodoptera frugiperda originates from the (sub-)tropical regions of the Americas. The adults are good fliers and migrate each summer over very long distances, into the North as far as Canada.
Once they have arrived in late summer or autumn, they may have one to several generations locally, but they cannot withstand even slight frost. In the tropics, they are active throughout the year. Each female lays about 1,000-2,000 eggs in clusters of up to 400 at night, usually on leaves or on light-colored surfaces. The egg mass is covered with grayish scales from the female's abdomen. The development of all eggs within a mass usaually needs 3-7 days.
After consuming the remains of the egg mass, the newly-hatched larvae disperse in search of food, often using a silken thread to reach the ground. Over a 2-4 week period they pass through six, occasionally only five, instars. They feed in daylight too, but tend to spend the warmest part of the day hidden from the sun. Older larvae become cannibalistic, thus only one or two of them are found on each plant.
For pupation, the mature caterpillar burrows 2-8 cm (0.78-3.15 inch) deep into the ground, where it builds a loose cocoon from silk and earth particles. If the soil is too hard, the larva remains on the surface and uses plant material. The pupal stage lasts from eight to 24 days.
The adult moths emerge at night. They usually fly many kilometres during their pre-oviposition period of 3-4 days. They live up to three weeks.
Additional Crop Information
S. frugiperda has a very large host range but it obviously prefers grasses.
Among the crops attacked are small grains, soybean, sugarcane and bermudagrass, but it is also frequently found on tomato, alfalfa, peanuts, spinach, clover and many others.
The impact of fall armyworm varies between regions and years. In the event of a severe outbreak, damage can be great.
Useful non-chemical contribution to Integrated Weed Management
The most important cultural practice to reduce damage is early planting (if possible of early- maturing varieties) in order to escape the peak of fall armyworm immigration.
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