Homeowners in Cullman County and across North Alabama who are seeing dead or damaged lawns may be facing an infestation of fall armyworms.

According to the Alabama Cooperative Extension System, recent numbers indicate that this year’s occurrence of fall armyworm populations is the worst it has been in nearly four decades.

Alabama is experiencing a high number of migrating fall armyworm moths, and the state has experienced numerous rainfall events to put the yearly total above average. This frequency of rain creates a favorable environment for fall armyworm eggs and larvae to survive in large numbers. It also creates lush, green fields that attract armyworms.

People may find populations in home lawns, turf, field crops, and pastures. Infestations are especially common in well-managed bermudagrass.

To help homeowners and farmers identify a potential armyworm infestation and hopefully deal with the worms before they cause too much damages, ACES has released a few guides detailing the best steps to take. 

Identifying armyworms

Properly identifying a pest is the first step to finding a control option, and fall armyworms have a few distinct characteristics that make this job easier.

“A fall armyworm’s head has light markings that form an upside-down Y,” said Katelyn Kesheimer, an Alabama Extension entomology specialist. “On the opposite end, they have four black dots that form a square.”

Well-maintained, fertilized lawns are like an all-you-can-eat buffet for fall armyworms. In a flash, they can completely strip a lawn and move on to their next target. That is why homeowners must be quick and efficient with their scouting and control.

How do you scout for fall armyworms? This task is fairly simple — know when and where to look.

“The best way to scout is by kneeling in the grass and looking for the caterpillars,” she said. “I recommend scouting during the cooler parts of the day when fall armyworms will be near the top of the grass blades.”

While not ideal, people can scout during the hot parts of the day. The caterpillars will be down near the soil surface during those times. Kesheimer said homeowners can use a soap flush to draw them out.

“To do a soap flush, mix 1 tablespoon of liquid dishwashing soap in 1 gallon of water,” she said. “Using a watering can, pour the soapy water over a 1- to 2-square-foot area. If present, the larvae, will emerge from the soil or thatch.”

Controlling armyworms in your yard

Ideally, it is best to find fall armyworms when they are smaller than ½-inch long. The smaller they are, the easier they are to control.

If most of the caterpillars are large (1 to 1.5 inches), then it is likely too late to control the population. They will cycle out and move on to “greener pastures.” If the population is mostly small caterpillars (0.25 to 0.5 inches), they may not require as extreme measures in order to manage them. 

When looking for control products for lawns, note that most product labels will list that they are for control of caterpillar pests, rather than specifically for fall armyworms.

“Granular formulations of pyrethroids are the most used methods of control, but there are some spray formulations available,” Kesheimer said. “When using a granular or a ready-to-spray formulation, no dilution or equipment is required.”

Products containing spinosad or Bacillus thuringiensis (Bt) will control smaller caterpillars without harming beneficial insects. However, Bt will only provide control for one to two days. The recent rains could also affect fall armyworm control, as pyrethroid chemicals stop providing control after a rain event. 

Controlling armyworms in your fields

When producers find armyworms, quick and efficient control is crucial. As Kesheimer points out, these pests are called armyworms for a reason. They are exceptionally fast and efficient when consuming forages.

There are multiple control options for fall armyworms in pastures, including mechanical and chemical options.

“If a hayfield is close to harvest, the producer should go ahead and harvest early as a mechanical control option,” she said. “Cattle can also be used to intensively graze the forage before the caterpillars consume it all.”

When it comes to chemical control, the right application largely depends on where the producer plans to use it. Chemicals vary in price, residual control and level of rainfastness (the time needed between an application and a period of rain). Kesheimer offers the following recommendations for armyworm control in pastures and hayfields:

– Insect growth regulators. Products that contain diflubenzuron (Dimilin) or methoxyfenozide (Intreprid) are insect growth regulators. They control the pest by disrupting its life cycle. They are best for controlling small caterpillars. Residual control for diflubenzuron products is approximately 10 days. Residual control for methoxyfenozide products is seven days. Both will cease to provide control following rain.

– Pyrethroids. Common pyrethroid products include Mustang Maxx, Karate and Warrior II. These chemicals will provide more immediate knockdown but have shorter residual control. They will also stop providing control after rain.

– Chemicals that are more rainfast. If the frequency of rain in the state continues, producers should consider applying products that are more rainfast. Products containing chlorantraniliprole, such as Prevathon and Beseige, are taken up by the plant, so they will still be effective after a rain. These products are more expensive, but they offer longer control, up to 21 days at the highest labeled rate.

Controlling armyworms is not as simple as spraying the chemical and forgetting about it. Producers must monitor their fields after making an application to see how it affects the caterpillars.

If a producer does not see near immediate results, they should not panic. All chemicals have different modes of actions, and it may take longer for some of them to start working. This is why understanding all the details about the chemical is important.

There may be some instances where the application does not fully control the infestation, and a second application may be necessary. For example, if there was a rain event and a systemic insecticide was not used, Kesheimer said a second application should be done.

However, it is important to remember that if a spray failure does occur, do not use the same mode of action. For example, if a producer uses a pyrethroid and control was not achieved, they might use a carbaryl product for the second application.

A full list of chemical control options for lawns and fields, as well as more information on scouting and control, is available in the Alabama Extension publication Controlling Fall Armyworms on Lawns and Turf, which can be found at the ACES website at aces.edu.