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Learn Your Lawn: Armyworms

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Armyworms are a type of caterpillar that is destructive to crops, particularly turfgrass, corn, and wheat. They are called Armyworms because of the way they move across lawns in large groups or "armies,” devouring plants as they go. Armyworms are the larval stage of a moth, which is native to North America and can be found east of the Rocky Mountains, reaching northward into southern Canada. Armyworms are typically green or brown in color and have a smooth, segmented body that can grow up to 2 inches long. They are identified by a distinguishing dark line running down the middle of their back.




Armyworm Moths migrate from the southern United States in April and May. They are active during the evening, feeding on nectar, mating, and searching for areas like your lawn to lay their eggs. 

  • Egg Stage: Eggs are deposited in rows or clusters on the lower leaves of grasses or at the base of plants. Eggs hatch in 1 to 2 weeks.

  • Larva Stage: Larvae are active at night, feeding on turfgrass plants. During the day, they can be found under plant debris or in the top few inches of the soil.

  • Pupa Stage: After completing six instars, larvae pupate just below the soil surface. 

  • Adult Stage: Adults emerge in 1 to 2 weeks. A second generation occurs in late June or early July, and a third occurs in late August or early September.


Armyworms can be difficult to identify and may become a significant problem if left undiagnosed. A change in cultural practices can help deter these pests. However, once the lawn is infested, treatment may be necessary to eliminate the problem.


A thick, healthy, well-maintained lawn is always the best line of defense. This can be achieved through beneficial cultural practices, which include:

  • Watering: Deep and infrequent watering is essential for strong plant health and development. A general rule of thumb is to water each area of your lawn for 30-45 minutes, twice per week, in the early morning so the turf is dry by nightfall. 

  • Mowing: Maintain a regular mowing schedule throughout the growing season. In general, you should keep your lawn between 2 ½ and 3 ½ inches high, but during the hottest weeks of summer, you may allow the grass to grow as high as 4 inches. Never remove more than ⅓ of the grass blade at each mowing.

  • Fertilizing: Regular applications of Weed Man’s specially formulated, slow-release granular fertilizer will help provide your lawn with adequate nutrients. These applications are timed specifically to avoid over fertilizing the lawn.

  • Core Aeration: Aerating your lawn can improve soil drainage and help reduce the likelihood of insect infestations. It will also alleviate soil compaction and allow water and nutrients to penetrate deeper into the soil.


Your local Weed Man professional may be able to offer other solutions and recommend the best form of treatment that is available to improve the conditions of your lawn.