Armyworms

Armyworms are not militant red wigglers. Instead, they are the larval form of the fall armyworm moth, which can wreak havoc on Bermuda grass lawns and several garden plants.

Fall armyworm moth larva (Frank Peairs, Colorado State University, bugwood.org) CC BY 3.0 US

Until recently, armyworms (Spodoptera frugiperda) were only found in South America, Florida, and southern Texas. Now this pest is found throughout North America. Warmer areas will have more of a problem with armyworms because northern populations are limited by freezing temperatures. ​

Fall armyworm moth (Donald Hobern) CC BY 2.0

Fall armyworm moth (Wikipedia) Public Domain

Armyworm identification

Armyworms go through complete metamorphosis. They begin life within a dome-shaped egg. Adult females lay masses of 100 to 200 eggs, with an average of 1500 eggs in her lifetime. Some overachievers lay more than 2000 eggs! These egg masses are often covered with a layer of grayish scales that make the cluster look moldy or fuzzy. When armyworm eggs hatch, the larvae, which grow to 1-1/2 to 2 inches in length, go through six stages, or instars, that feature specific characteristics:

• First instar - Larvae are greenish with a black head 
• Second instar - The head turns orange
• Third instar - Larvae turn brown with white lateral lines
• Fourth through sixth instars - The head turns reddish brown with white mottling; white lateral and sub dorsal lines become more pronounced; an invert “Y” shape can be seen on the face; elevated spots with bristles occur on the body

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Since pupation normally takes place in the soil, you may never see an armyworm’s reddish brown cocoon. Adult armyworm moths look grayish-brown at rest, with an average length of 1 to 1-1/2 inches. On male moths, you may be able to see white triangular spots at the tip of each wing.  

​Signs of armyworm damage

For the most part, armyworms eat the leaves of grasses and small grains. They have also been documented feeding on corn, peanuts, beets, apples, oranges, strawberry plants, peaches, and grapes. In the first instar, larva eat only one side of a leaf’s epidermis. By the second and third instar, they eat holes in leaves and they eat from the outer edge inward. Cannibalistic tendencies usually prevent complete defoliation (leaf loss), but not always. In some cases, large numbers of eggs hatch at the same time, creating an army behavior that can destroy an entire field within days.

How to control armyworms

Luckily for us, armyworms have many natural predators, most of which are parasitic wasps. Earwigs, soldier bugs, ground beetles, birds, skunks, and rodents all enjoy a meal of armyworm larvae or pupae. Pheromone traps can be used to determine if armyworm moths are present. If they are, it is a good idea to inspect susceptible plants for egg clusters and feeding larvae, which can be removed by hand in garden settings. Commercially, insecticides are applied (sometimes daily) to Florida corn to prevent armyworm damage.

I guess I'll have to start growing my own corn now, too.