Armyworms are invading our lawns


Ohio State University Extension offices across the state have been receiving e-mails and phone calls about Fall Armyworm (Spodoptera frugiperda, family Noctuidae) causing substantial injury to turfgrass. Lawns are totally stripped of grass leaving dead areas in its wake.

In Wood County, we believe the adult moths arrived about five weeks ago. They came up from the south carried by the jet stream, most likely on a southerly storm front. Moths are known to travel 500 miles or more in a 24-hour period.

For reasons only known by the Armyworm moths, they descended upon Ohio.

The female moths tend to lay eggs on the flat leaves of trees and flowers that overhang turf, especially turf that has been recently fertilized. Each adult female can produce an egg mass that contains 100 to 500 eggs. The females are also attracted to night lights, and they will attach their egg masses to the light posts.

If there are large areas where no plants or structures are overhanging the turf, the females will lay strips of eggs on grass blades. The eggs hatch in five to seven days, and the larvae or worms usually take three to four weeks to complete their development known as the pupation stage. Depending on the date of their exact arrival and when the female moths laid her eggs, we should be close to the pupation stage.

When the eggs hatched, the Armyworm larvae or worms have the potential to devour an entire lawn.

The larvae move en masse across the turfgrass. The larvae will continue feeding until there is no more food or they complete their development, whichever comes first.

Lawns that have had the canopy removed by the caterpillars will have the crowns and upper roots exposed to direct sunlight. The crown rests on the soil surface and is the growing point for both blades and roots. On sunny, warm days, the area where the crowns are located can easily reach 120 to 130-degrees F which will “cook” them or dehydrate them.

Loss of the crowns means the loss of the entire turfgrass plant. If this happens, the lawn is dead and will have to be reseeded.

To check if you have an active infestation of Armyworms, pour some soapy water on your lawn. When you pour soapy water over a patch of grass (1/2 ounce dishwashing soap/gallon water), the solution will irritate the larvae, which will drive them up from the soil surface very quickly. Heavily infested turf will also have visible greenish-black fecal pellets, or “frass,” on the soil surface.

The first step in protecting your lawn is to kill the caterpillars before they completely devour the turfgrass canopy. This involves the direct application of insecticides.

Armyworms tend to feed in the morning and late afternoon and evening. Applying a liquid Synthetic Pyrethroid insecticide to your lawns in the morning should give control. Synthetic Pyrethroid products available for home use include one of these active ingredients: Bifenthrin, Cyfluthrin, gamma-cyhalothrin and lamba-cyhalothrin.

If you missed the first step, the second step is to save the crowns. The crowns without the grass canopy can dry out so watering the damaged areas in the heat of the day will keep the crowns cooled down and hydrated.

Apply enough water to hydrate the crowns without saturating the soil, however, apply enough water to keep the root zone moist. This should be kept up daily until a visible green cover returns to shade the crowns. To aid the grass recovery effort, an application of a fall fertilizer product will help. The fertilizer should include a slow-release form of nitrogen to support turfgrass growth over a longer period of time.

If there is a concern that crowns are being lost — for example, if irrigation is not possible due to various reasons — now is the time to look for grass seed as the supply of seed is down this year.

However, here are a few points to consider.

While perennial ryegrass (Lolium perenne) will germinate quickly and provide rapid cover of damaged areas, the Ohio State University Turf Grass Team is seeing a fair amount of grey leafspot which is killing perennial ryegrass across Ohio.

Current recommendations from the team are use a slit-seeder also known as a slice seeder to seed turf-type tall fescue (Festuca arundinacea). If possible, a blend of multiple cultivars should be used. The cultivars that have been developed in recent years have a color and texture that match Kentucky bluegrass (Poa pratensis). Also, most turf-type tall fescues have endophytes that produce alkaloids that are toxic to armyworm and sod webworm caterpillars, as well as other insects that feed on grass blades such as chinch bugs and billbugs.

These seed products may have “endophyte-enhanced” on the bag or indicate the cultivars are resistant to insects. Depending on weather conditions, the cutoff date for seeding lawns in Northern Ohio is Sept. 15.

On a final note, OSU entomologists are concerned. The good news is the Southern Armyworm infestation does not survive Ohio winters. The bad news is there may be another hatch in mid to late September.

The current Armyworm infestation will pupate, and the adult moths will mate and lay eggs again. Of course, a frost will kill the larvae. Without knowing our fall weather conditions, it is crucial we keep monitoring our lawns for the Armyworm.

Remember, it is up to the user to read and follow all pesticide labels.

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