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 Farmers
Should Be on Look Out for Fall Armyworms
Auburn,
July 25, 2002---Fall
armyworms have worked their way across southern Mississippi and have
made their 2002 appearance in Alabama. Dr. Kathy Flanders, an
entomologist with the Alabama Cooperative Extension System, says the
chronic pest has been discovered in fields in Mobile County.
Flanders says it's
typical for the first reports of fall armyworm damage to come from
south Alabama in late July or early August.
"Fall armyworms
prefer lush, well-fertilized bermudagrass. Check your bermudagrass
fields regularly for caterpillars or the appearance of brown
circular patches," says Flanders. "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 the 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. Some
of the fall armyworms may be curled up in the leaf litter, so be
sure to look 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 most
of 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 make sure
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.
She also points out that
fall armyworms will attack bermudagrass lawns just as they will
bermudagrass pastures and hayfields. 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 from
county Extension offices.
Source: Dr. Kathy
Flanders, Entomologist, Alabama Cooperative Extension System,
(334) 844-6393
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