For area farmers battling the invasive, pasture grass-annihilating fall armyworm caterpillar, University of Arkansas Division of Agriculture Research and Extension (UAEX) held a special presentation Monday to aid anyone seeking tips on curbing the species and its effect on local livestock grazing lands and seasonal hay production.
The caterpillars, or fall armyworm larvae, are migratory in nature. They originate in America in south Texas and typically move north and northeast into southern Arkansas around the fall harvest.
By consuming vast amounts of grass, the species can often damage crop, grassland, and hay production. They feed mostly on lush bermudagrass and threaten small grains and ryegrass for winter wheat. If those variations of grass, though, are not present, the small nuisance can and will feed in most any grass type in the area.
The fall armyworm is identifiable by the “inverted-Y” marking on its forehead. It’s length can also grow from under half an inch to 1.5 inches. From there, it pupates into a moth. If at least three fall armyworms are found per square foot in a pasture or grassland, chemical steps are typically needed to stamp out their effects.
To find out if a pasture is indeed infested with the fall armyworm, according to UA Extension data, at least 10, one-square-foot sections should be examined at random across a field. The most prevalent area for egg-laying is also in areas of “abundant growth.”
“Clues to infestation — especially if you have a lot of small worms — early on will look like the field is frosted,” said Dr. Kelly Loftin, entomology professor at the University of Arkansas. “And sometimes you will see a field that almost looks like drought damage – look for armyworms.”
Other signs of fall armyworm infestations include heavy bird feeding in a pasture, and, in severe cases, the smell of fresh-cut grass emitted. If the caterpillars are at least a half-inch in length and at least three exist per square foot, treatment is needed.
If they are significantly larger than that, then the “damage is probably already done” said Loftin, and they will soon begin their metamorphosis stage. The lifestyle of the armyworm is typically 30 days in warmer weather. The cooler the weather becomes though, the longer the maturity process lasts and their lifespan can extend.
Home remedies for smaller caterpillars are not recommended, according to Loftin. The entomologist on Monday also dispelled the treatment method of bleach mixed with Dawn-brand dish soap.
“We know they don’t work,” he said.
For ground control applications, cutting for hay is by far the cheapest way to temporarily eliminate armyworms from an area. For a longer-term solution, however, insecticides are needed.
“It’s important to have products with residual activity, especially when you have those big sizes of worms,” Loftin added. “Because you’re potentially going to get reinfestation more often.”
Besiege brand insecticide (roughly $18-$22 per acre) containing lambda-cyhalothrin may be on the more expensive side, but its results are significantly better than others tested in the region.
“Basically, you’ve got about 26 days of residual activity in the Besiege mixed with lamda-cy,” said Loftin. “That’s enough to make a full crop.”
There are also no grazing restrictions when using the substance and hay can be harvested at least seven days after its application, the UAEX guide says.
New insecticides, though, are becoming more and more difficult to pass EPA standards, plus the caterpillars are gaining a slight tolerance to their effects. They are regularly blasted with the chemicals south of the border, then the surviving species make their way to our area. To fight this, a different, much more devastating and less hazardous approach has been taken by scientists and biochemical companies.
By spreading and developing a nuclear polyhedral virus, or NPV, specific only to fall armyworms, farmers could see a far cheaper alternative to wiping out the infestation. And at only an estimated $3.50 per acre coverage, no other organism is harmed.
“It kills fall armyworms and that’s it,” said Dr. Gus Lorenz, an entomology professor and coordinator at UAEX. “These are very effective in very, very small quantities.”
With the new product called Fawligen, developed AgBiTech with input from Lorenz and other entomologists, roughly 7 billion virus cells can be spread with 2 ounces of sprayable compound per acre. It’s effects also last across generations of larvae due to its spreadability via other carriers. To say the least, viral elimination of fall armyworms is becoming a more and more attractive control method for landowners.
“It’s the wave of the future,” Lorenz added.
But the application does have some drawbacks. Since the NPV is a living organism itself, it must be stored at cool, below 77-degree temperatures before application.
“You can’t just throw this stuff in the sprayer in the back of your truck and let it sit there for two weeks,” Lorenz said. “It can’t survive like that and it can’t survive out in the sunlight for long periods.”
The scientist did add that the application can easily withstand the brief time needed to apply it to a field or crop, but just not long periods out of optimal conditions.
The virus does, though, take slightly longer to eliminate the pests since it works through an organic sickness to the caterpillars. Once the larvae themselves are deceased, the compound is not finished working.
By natural means, the virus can spread across a pasture. Insects can carry it to other sections, along with migrating armyworms cannibalizing their own dead. The elimination all comes at no risk to any other animals, including grazing cows, mammals, and others.
“This virus simply does not harm anything other than fall armyworms,” Lorenz said.
He also said it cannot mutate.
Although the product is available for purchase now at dealers and through the company, the UAEX entomologist said that his tests have not resulted in 100-percent success-rate yet and a more potent virus is currently in development.
“We’re screening isolates with the company right now and trying to find a more active virus,” he said. “They have a product for sale, but I’m not quite satisfied with the control I’m getting in my plots right now, but I think we’re going to get there.”
The ag scientist added that a newer, better product is on the horizon.
“It’s coming, I promise,” he said. “We’re going to make it available and we’re going to try to save y’all some money when dealing with these fall armyworms in the future.”
For more information on fall armyworm management, contact the Columbia County UAEX office at 870-235-3720. or download online factsheets and pasture management guides at UAEX’ website at www.uaex.edu/farm-ranch/pest-management/insect/armyworms.aspx.