usually predict outbreaks of armyworm, Mythimna
unipuncta, in Alabama. That is
because cool, wet springs favor the growth of large populations of this insect
pest. It has certainly been wet enough,
although I am not sure it has been cool enough this spring. Still, I think it will be worthwhile to keep
an eye on grassy crops such as corn, sorghum, small grains, and grass forages
for the next month or so.
Armyworm is often called
true armyworm so not to confuse it with the fall armyworm. Armyworms vary in colorations but usually
have several dark stripes. The head of
an armyworm caterpillar is light colored, with a mottled or netted pattern. In profile, the head is rounded.
This insect overwinters
as a partially grown caterpillar. In
early spring, the insect pupates then transforms into a moth. Moths lay eggs in clusters of 2-5 rows on
sheltered places in grass foliage.
Larvae hatch in a few days and begin to feed on the foliage. Hungry caterpillars will march to find new
food sources, as shown by the flattened corpses on the roadside in the image below.
It is important to catch
these insects when they are small, before they have time to do too much damage.
Approximately 80% of the damage from
this pest is done by the largest sized caterpillar, in its last few days of
feeding. Small larvae skeletonize the
foliage, but by the third instar begin to eat holes in leaves. When they molt into larger sizes they can
consume entire leaves. Symptoms of this pest on maturing small
grains include heads where the awns have been eaten, and heads that have been
clipped off. Caterpillars tend to do
most of their feeding at night, and may hide in crop debris during the day.
If you find armyworms,
here are some guidelines on whether there are enough insects to treat with an
Treat if 25% of the plants have feeding
Treat when larval numbers exceed 4
larvae/sq ft before pollen shed and 8 larvae/sq ft after pollen shed.
Treat if there are more than 2-3 per square
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