AUBURN UNIVERSITY, Ala. – Alabama forage producers must feel like punching bags at this point. The recent rainfall has kept many producers from harvesting their hay. Now fall armyworms are plaguing many areas of the state, threatening to devastate forages in both pastures and hayfields. Some Alabama Cooperative Extension System professionals say this is the worst infestation the state has seen since the early 70s. This has producers scrambling to make sure their farm is not next on the menu.
Rain Not Helping
The long periods of persistent rains in the state are creating a thriving environment for armyworms. Also, in some cases, the rain has prevented producers from getting into their fields to control an infestation.
“Fall armyworm eggs and larvae are able to survive in large numbers thanks to the frequency of rainfall the state has seen,” said Katelyn Kesheimer, an Alabama Extension entomology specialist. “The rain also creates a lush, green smorgasbord for armyworms to feed on.”
Scouting, Scouting, Scouting
Time is of the essence. Producers must start scouting for this insect pest now. If not detected early, fall armyworms can completely decimate a field seemingly overnight.
“Scouting is the best way to determine if and how many fall armyworms are present,” she said. “Some great ways to scout for the caterpillars is by getting on your knees and looking or by using a sweep net.”
It is best to scout during the cooler parts of the day when the caterpillars will be actively feeding. However, producers can look for armyworms down near the soil surface during the hotter parts of the day. When scouting, note both the size and number of fall armyworms. This will greatly affect the needed control strategy.
“Ideally, you want to find them when they are smaller than ½-inch long. The smaller they are, the much easier they are to control,” Kesheimer said. “Producers can also look for damage the caterpillars cause, which will appear as jagged grass edges.”
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.
“If producers do not plan to harvest for another 10 to 14 days and have multiple generations of armyworms, they should consider mixing a pyrethroid and an insect growth regulator,” Kesheimer said.
- 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.
Whichever chemical a producer chooses, Kesheimer said that it is important to make applications late in the day, rather than in the morning. This will allow the armyworms to ingest the chemical while they eat overnight. A list of products labeled for pasture and forage control of armyworms is available in the Alabama Extension Pastures and Forage Crop IPM Guide.
Potential Control Issues
There are several things that can go wrong or producers can experience when trying to control armyworms.
As mentioned above, pyrethroid applications stop working after a rain event. While they are a control option, Kesheimer recommends that producers avoid using them if they can.
“We have seen some reports of pyrethroid applications failing to control armyworms, some experiencing less than 50 percent control,” she said. “While there could be several factors that caused these failures, including applicator error, I would recommend choosing another control option.”
Availability of chemicals may also be an issue for some producers. Currently, there have been some reports of availability issues in north Alabama. If this is the case, it is a good idea to have a backup plan. Kesheimer said that producers may have to use a generic pesticide.
If availability is an issue in their area, producers can also work with the Alabama Extension animal sciences and forages professionals that serve the area. They can help producers create an adequate management plan.
I Have Sprayed. Now What?
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.
For more information about controlling armyworms, check out Managing Fall Armyworms in 2021 or the Extension publication Management of Fall Armyworm in Pastures and Hayfields, both available on the Alabama Extension website, www.aces.edu.
Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.