We tend to have common armyworms in Ohio each year in late summer and early fall. They are typically a problem in new wheat fields, pastures and on golf courses.
They eat leaf blades, leaving brown swaths. I have also seen damage on ornamental grasses and corn.
Fall armyworm damage on a lawn in the Miami Valley. CONTRIBUTED/PAMELA BENNETT
However, this year we have had a huge outbreak of these caterpillars around the state. Entomologists suspect that the small brown moths flew in on one of our recent storms that came from the south.
This species of fall armyworm originates in South America and catches storms and migrates north. It is a much bigger pest in the southern part of the country. The last time I saw populations this big in Ohio was around 2015.
The moths lay their eggs in masses around lawn areas; they prefer turf that is watered, thick and lush. Because we have had such great periodic rains and most turf has not gone dormant, almost any lawn could have been selected by the moth.
When eggs hatch, caterpillars are tiny. It takes about five to six instars (stages of growth) for them to mature. While they are tiny, they feed on the grass blade, but do not consume the entire blade.
When they get to the five and six instar, they are voracious eaters. They consume entire lawns quickly. If there is no more lawn around, they consume each other.
Lawns should be treated with a product that kills armyworms. Lawn products that contain bifenthrin, beta-cyfluthrin, lambda or gamma-cyhalothrin, permethrin, deltamethrin or other pyrethroids. Follow label instructions.
I know that not everyone wants to use pesticides in their landscape. However, by following the label instructions and applying this time of the year, you will not be affecting pollinators.
Most clover and other blooming weeds that pollinators feed on are not in bloom, therefore, pollinators won’t encounter pesticides. Not using pesticides in this case will result in a poor-quality lawn.
If you are reading this column, it’s very likely that these armyworms have already done the damage. If you want to be sure that you don’t have them, take a gallon of water and mix in a tablespoon of dish soap.
Pour this mixture over a four-by-four-foot area of lawn. If the caterpillars are present, the soapy water flushes them to the top. Act by spraying to prevent major damage. Don’t apply pesticides if you are not seeing the caterpillars.
Fall armyworms don’t kill a lawn as they don’t eat the crowns of turf plants. However, exposure to hot sun and drying winds will finish the lawn off. Keep the crowns consistently moist and they will begin to grow. Thankfully the weather has cooled a bit as this helps recovery.
Ohio State University entomologist Dr. Dave Shetlar also noted that you may be on the lookout next season in early August as these sometimes turn up a year after the first mass attack.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at firstname.lastname@example.org.