August 14, 2012
Veteran Alabama farmers and producers know that hot, dry weather can be the perfect scenario for fall armyworms.
Kathy Flanders, an entomologist with the Alabama Cooperative Extension System, says this chronic pest was first spotted in May in Sumter County. But she says the problem only began to escalate in mid-July.
The pest was found in Jefferson County in mid-July. By July 17, Flanders says farmers and Extension agents had found fall armyworms in Baldwin, Chambers and Randolph counties as well.
"It started back in July, and the spread has not let up since then," says Flanders. "So far, more than a third of the state's counties are experiencing an outbreak of fall armyworms." You can see just where the worms are on the move with this interactive map.
She says that fall armyworms prefer lush, well-fertilized bermudagrass, and she encourages producers to check bermudagrass fields regularly for caterpillars or the appearance of brown circular patches.
"The first clue of an infestation may be the appearance of brown circular areas about 10 to 20 feet in diameter in an otherwise healthy hayfield or pasture."
She says the areas will enlarge quickly as the caterpillars eat the available food and spread outward in search of more food. From a distance, these patches can look like drought stress.
Fall armyworm caterpillars will feed on almost all forage grasses, as well as corn, cotton and approximately 100 additional plant species. The caterpillars develop into moths that lay eggs, beginning the cycle again. In Alabama, there may be as many as five to six generations of this pest every summer.
Fall armyworms can be found on foliage at any time of day, but may be more easily detected early in the morning or late in the afternoon. In heavy infestations, you will see caterpillar droppings on the ground.
Color may vary
When fully grown, fall armyworms are 1.5 inches long. They are always striped, but their coloring is not always the same. Their background color ranges from light green to almost black.
You can identify fall armyworm caterpillars by four black dots on the back of the tip of the abdomen. Larger caterpillars typically have a light-colored, upside-down Y-shape on the head and three white lines on top of the segment just behind the head.
"The earlier an infestation is detected the better. Young fall armyworms under a half inch in length don't eat much," says Flanders. "As the caterpillars get bigger, the more they will eat, and the bigger they are, the harder they are to control."
She encourages farmers to regularly scout fields now if they have not already begun doing so. She emphasizes that scouting is particularly important with the hot, dry weather affecting most of the state.
Flanders says that using a sweep net is only one element of effective scouting.
"Remember, finding them in the sweep net is the first step. You will need to verify that finding by seeing how many caterpillars you have per square foot. If you find more than 2 or 3 per square foot, the armyworms should be controlled."
Fall armyworms need to be treated when they are still small — no more than 0.5 to 1 inch long. Detecting infestations when the caterpillars are small gives more time for control measures to be implemented.
She also points out that fall armyworms will attack bermudagrass lawns as well as bermudagrass pastures and hay fields. Homeowners with bermudagrass lawns should scout their grass for these pests just as a farmer would.
Farmers and others can get more information on the biology and habits of fall armyworms in Alabama Cooperative Extension publication ANR-1019, "Management of Fall Armyworms In Pastures and Hayfields," available online and from county Extension offices.
Producers can learn to use a sweep net in this Extension YouTube video.
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