Armyworm Infestation Signs and Prevention

Armyworm outbreaks happen in the U.S. every 3-5 years, but this year’s infestation is severe. Entomologists from Ohio State University say that armyworms are picked up from southern states and carried through the jet stream to northern states. Due to cooler atmospheres in the upper part of the jet stream, the armyworm in the moth stage of their lifecycle go dormant during travel, and only continue their lifecycle once in the lower, warmer surfaces of the jet stream. 

Armyworms are a semi-tropical species that look like caterpillars. Adult armyworms lay eggs and turn into moths. It takes 20-40 days to complete larval development, the pupa takes 2 weeks to mature, and adults live from 1-3 weeks. The outbreaks come in waves about 4-5 weeks apart and can have anywhere from 2-5 waves a year. Armyworms cause the most damage at the worm stage of life. They will destroy and discolor turfgrass. The worms feed on leaf tissue, attack large areas at once, and move quickly, so damage can be extensive. 

It’s critical to recognize the infestation quickly to prevent irrepealable damage. Have customers carefully monitor their lawns and call you for services immediately if they see telltale signs of armyworms. If armyworms are suspected, customers can test for them by pouring a mix of soap and water on a patch of lawn; the worms will rise to the surface if they are there. 
 

Signs of armyworms:

The first sign is usually birds (typically starlings) pecking the lawn to eat the wriggling worms as they emerge into adulthood. Be sure to also look at the blades of grass- if there are brown spots with bitten tops of the grass blades, armyworms are probably the culprit. Mow customers’ lawns regularly, and be sure irrigation is in regular use. Have customers walk on their lawns daily as a preventative measure. Remove any thatch and grassy weeds so it’s less ideal for laying eggs. Thatch is also a hiding place for younger armyworms; the older worms will continuously eat throughout the day. 

Put an insecticide application down with active ingredients like bifenthrin for immediate control of armyworms, especially if grass starts to die. For immediate control of existing outbreaks of armyworms, apply an insecticide like LESCO Crosscheck or Provaunt WDG. If the turf is already dead, you’ll need to aerate the lawn and re-seed, although you should wait to do this until the armyworms are eradicated and the second wave has passed. For season long control and best results, apply Acelepryn early as a preventative application. 

If your customers are dealing with an infestation, visit SiteOne.com/pestmanagement or your local branch today. Associates are always available for questions or recommendations.