First, it was the drought. Then, it was the heat. Now, it is insects. Alabama cattle producers have been battling problems since last summer.
Fall armyworms are appearing now in pastures in Alabama. Kathy Flanders, an entomologist with the Alabama Cooperative Extension System, says the chronic pest has been discovered in fields in Coffee, Walker and Macon counties.
Flanders says it's typical for the first reports of fall armyworm damage to come in about this time of year.
“Droughty conditions create a favorable environment for fall armyworms,” says Flanders. “During the dry summers of 1999, 2000 and 2006 we saw many bermudagrass and bahiagrass fields that were damaged as early as July. Subsequent generations of the pest did damage in August and September in those years.”
This year, those armyworms are marching through pastures and hayfields weakened by two years of drought and a summer of blistering heat.
Don Ball, an Extension forage agronomist, says stress on forages has a cumulative effect.
“Many pastures were already under stress from last summer’s drought and overgrazing,” says Ball. “Now this summer, they are again being stressed by drought, high temperatures, grazing and insect pressures.”
He says this continued stress can thin forage grass stands and reduce productivity.
“This weather is taking its toll on all of our forage grasses,” says Ball. “Warm-season grasses such as bermudagrass are faring better than cool-season grasses such as fescue.”
Ball adds that it is almost impossible to make a sweeping assessment of the overall state of pastures and hayfields in the state, although many are in bad shape at present.
“There are so many factors that will influence condition,” he says. “Factors such as the age of the stand, the variety and the amount it has been grazed as well as the weather will influence condition.
“This fall, producers will need to evaluate all of their pastures and fields. Without a critical evaluation of the stand, a farmer cannot determine the best way to manage the field.”
Ball notes the effects of the recent and current stresses will be felt for a number of years.
“Pastures didn’t develop problems overnight. The solutions to those problems are not going to happen overnight either.”
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. Look in the leaf litter. Some of the fall armyworms may be curled up there.
When fully grown, they are 1.5 inches long. Fall armyworms 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, their food demands increase dramatically and the bigger they are, the harder they are to control."
She encourages farmers to begin regularly scouting their fields now for fall armyworms if they have not already begun doing so. She emphasizes that scouting is particularly important with the hot, dry weather affecting the state.
Scouting for fall armyworms is a relatively simple process. Walk into the pasture from all four sides or walk in an X pattern across the field to ensure you check a large enough area. Stop at about 10 places in the field, and look closely for small caterpillars feeding on the grass. If you find them, estimate the number per square foot.
Flanders says control of fall armyworms is justified when the population exceeds three 0.5-inch caterpillars per square foot. Fall armyworms need to be treated when they are still small — about 0.5 to 1 inch long. Detecting infestations when the caterpillars are small gives more time for control measures to be implemented.
When armyworms are fully grown, they are less susceptible to insecticides and, therefore, are harder to kill. In addition, if most of the caterpillars are nearly grown, most of the damage will already have been done.
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 from county Extension offices.