Fall armyworms invade pastures, hayfields and lawns every summer in Alabama. Some years, the damage done by these pests is mild. Other years, they cause widespread damage across the state.
Dr. Kathy Flanders, an entomologist with the Alabama Cooperative Extension System, says the spotty nature of late spring rains contributed to the current outbreak of fall armyworms.
“The hit and miss nature of late spring rainfall led to dry conditions in parts of the state,” says Flanders, who is also a professor in Auburn University’s Department of Entomology and Plant Pathology. “Those dry conditions allowed fall armyworm populations to build faster than the natural enemies of this pest could handle.”
She adds these pests which migrate here from the Caribbean and Mexico were first confirmed in Alabama in late June. Armyworm caterpillars have been found in more than 40 of Alabama’s counties.
“Right now, we are dealing with the second wave of fall armyworms,” Flanders says. “We usually expect a month between generations.”
But in years of extreme infestations, the generations of fall armyworms overlap, allowing for almost continuous egg laying. In this situation, caterpillars of all sizes can be found in affected fields and lawns.
“In these bad years, the monthly intervals when most of the damage occurs are not as noticeable.”
But Dr. David Han, an Extension turfgrass specialist, and Dr. Jennifer Johnson, an Extension agronomist both says the good news is that fall armyworms rarely kill lawns or pastures.
“In lawns, armyworm damage looks bad,” says Han. “It is rarely fatal, since they just defoliate the turf.
He adds that if the grass has healthy roots, stolons and rhizomes, it will recover once the armyworms are killed.
Johnson says well established stands should be able to recover from the defoliation.
“Armyworms are intense grazers,” says Johnson. “However, defoliation can lead to a reduction in forage available to livestock over the growing season.”
Fall armyworm damage seems to appear overnight. All too often, the first indication is the appearance of brown circular patches where the caterpillars have eaten all the grass.
Flanders, Han and Johnson agree that the best way to limit damage from fall armyworms is to scout lawns, pastures and hayfields for the caterpillars.
The easiest way is to try to find them using an insect sweep net. These heavy duty butterfly nets can be pushed or drawn through the grass to catch a portion of the insects that are present.
“Most county Extension offices and the regional animal science agents have sweep nets you can borrow,” says Flanders. A short video on how to use a sweep net can be found on the Extension YouTube channel.
In closely-mowed lawns, armyworms can be forced to the surface using a soap flush. Mix 1 ounce of lemon-scented dishwashing liquid in a gallon of water, and soak a small area of the turf with the soapy mixture. This will bring the armyworms to the surface within about 10-15 minutes.
Flanders explains that most damage from fall armyworm is caused over the course of about four days from feeding by the biggest caterpillars (3/4 inch long or larger). If you can find the armyworms during the 10 days or so when they are younger and smaller, your chances of controlling the pest are better.
Han says for lawns, homeowners should look for products containing pyrethroids or carbaryl and labeled for turf use to control the caterpillars.
“These will all do a good job killing fall armyworms provided they are applied correctly,” he says. “It’s the method rather than the product that fails most often. For good fall armyworm control, insecticides should be applied either at dawn or at dusk when armyworms are most active. Applications in the middle of the day are not effective.”
Farmers who are dealing with a fall armyworm infestation have more options. Learn more about these options in the Alabama Extension publication, Management of Fall Armyworms in Pastures and Hayfields or visit Insect Pest Management section of the Alabama Forages website.
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