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Armyworms in my Lawn

armyworm

Q. We suddenly have a large number of dark caterpillars on our lawn. What are they and how do we control them?

A. Black markings and a webbed pattern on the head identify this caterpillar as a true armyworm (Mythimna unipuncta), almost identical to the fall armyworm (Spodoptera frugiperda). A fall armyworm has an inverted Y-shape on its head and is found in larger numbers late summer/fall. Adult armyworm moths migrate north to Illinois from southern states to mate and lay eggs on the bottom of grass blades and other plants. Most years, weather conditions and natural predators control armyworms. When the larvae hatch in large numbers, however, they can eat their way across a lawn at an alarming rate. Healthy lawns are not usually permanently damaged as the insects eat leaves, not roots. Heavy infestations can easily be controlled with insecticides.

For more information about armyworms and control measures, please send an email to plantinfo@chicagobotanic.org or call (847) 835-0972.