Army Worm Infestation
Over the last week, we have seen an outbreak of fall armyworms in the Wabash Valley. In our 34 years in business, we have only had about a dozen lawns affected by armyworms. In the last week, we are seeing the largest outbreak since the 1970’s according to many universities. This email is intended to educate and inform our customers about what we are seeing in lawns and what can be done to help remedy the issue.
What, why, how?
We are seeing the larval stage of the armyworm infest the Wabash Valley. These caterpillar-type insects come in several colors but appear to be mostly black or brown with stripes. They will feed primarily on cool-season turf grasses and agricultural crops. As an adult, the armyworm is generally a gray moth with a 1 1/2 inch wingspan. Entomologists do not have a real answer to why Armyworms are so widespread this year other than weather patterns. Winds allowed for dispersal, and ideal moisture has allowed for high fecundity and survivability. Typically natural enemies help keep the population in check.
Since this is a very rare occurrence in the Wabash Valley, we are trying to learn as much as we can about this insect and the impact that it is having on lawns. Because of the life cycle, feeding habits, and resistance to pesticides, a preventative application would not have had any effect on the current outbreak. Not every lawn will be impacted by armyworms but it is good to understand them and know what to look for on your own.
The armyworms are only feeding on the foliage. Areas can look scalped, or they can brown out when foliage dehydrates quickly during feeding. The turf should recover. I’d fertilize it and encourage growth. If the crown is exposed, water lightly in the heat of the day to prevent the crown from drying out.
In the last week, we have made several service calls and discovered armyworm damage. It first appears as drought stress but can spread quite fast as the insect is feeding. Below are pictures of armyworm larvae, damage, and eggs.
There are a few easy ways to check for armyworms on your lawn.
1) Get down and dirty in your grass. Look for the actual worms. They are always on the surface of the turf and are about 1-2 inches long.
2) Pull the turf. If the grass comes up but the roots stay in the ground, that’s a very good identifier of armyworm damage.
3) Look for signs of armyworm eggs. These eggs look like white masses and are usually found on structures and buildings. I have found some this morning on our clothesline post as pictured above.
Armyworms feed on the leaf tissue but leave the crown and roots of the grass intact. Insecticide can be used to spray and kill armyworms to stop the current feeding damage, but it will not reverse the damage once done. Insecticides will only be effective in early instar stages of the armyworm. Once feeding begins, there is a very short window to successfully apply an insecticide that will kill the worm. Once you notice damage, the armyworm is usually on day 2 or 3 of their 5 day feeding cycle. It is almost always too late to apply an insecticide at this point. If you feel that an insecticide treatment is warranted, choose one that contains bifenthrin, cyfluthrin, or carbaryl (Sevin). Always read and follow all labeled instructions of any products that you apply. If you have questions, consult a professional licensed applicator.
Ultimately, irrigation and a proper fertilizer program will be the best thing for the turf to regrow and recover. Purdue University is not suggesting an insecticide treatment for our area as the armyworms will no survive in our climate and it is not expected for us to see any more generations to cause future damage.
The recommended recovery strategy is to irrigate, fertilize, apply insecticide (only if worms are still actively feeding on turf), overseed and aerate. Insecticide treatments at this time will not be effective as many of the armyworms have begun to dig into the soil to pupate.
The fall armyworms in the Wabash Valley is a very rare event. Entomologists have not seen a recorded infestation at this level in at least 40 years. Insecticide treatments may help, but only if the worms are small and actively feeding. The feeding stage of the armyworm lasts 4-5 days maximum. They only feed on the foliage and will not kill the plant. Proper irrigation and a healthy fertilizer program will encourage plant regrowth and lawns should recover over the coming weeks. If you decide to apply an insecticide, always read and follow all labeled instructions. Consult a licensed professional if you have questions.