Insect Management
Cotton Insect Management
Fall Armyworm -
Spodopterafrugiperda (J.E. Smith)
Description
The fall armyworm has four stages of development - egg, larvae, pupa, and
adult. The eggs are laid on plant foliage in masses of about 50 to several
hundred. They are deposited in layers on the top and bottom of leaves and other
plant parts. Egg masses are covered with grayish fuzz and range in size up to
1/2 the size of a dime.
The young larva is white at first and has a black head. The body becomes
dark with stripes as the larva grows. The larva sometimes resemble bollworms,
but have a much smoother appearance. The larva ranges in color from light green
to almost black, but is usually a light cream colored brown with stripes down
the length of the body. The head is dark and shiny and is marked with a
distinctive, light cream colored, inverted "y" on the front of the head. The
mature larva is usually about 1-1 /2 inches long. The pupa is a reddish - brown
color that later becomes almost black.
The fall armyworm adult moth is about 3/4 of an inch long and is dark gray
mottled with light and dark splotches. A noticeable white spot occurs near the
extreme tip of the front wings. The wingspread varies from 1 to 1-2/3 inches.
The hind wings are grayish-white and the front wings are dark gray.
Biology
Fall armyworm attack a wide range of host plants including bent grass,
bermudagrass, cotton, grain sorghum, corn, tobacco, peanuts, and soybean. Fall
armyworm egg masses hatch in two to four days depending on the temperature.
Young larvae feed in colonies for a short time immediately after hatching, but
then the larvae disperse to other parts of the host plant or to other plants in
the area. Young larvae often produce silk-like threads and drop from these
threads to other plant parts. Many that drop to the ground are killed by
predators or become infected by soil-inhabiting disease organisms. Development
from egg to mature larva requires two to three weeks. The mature larva burrows
one to two inches into the soil and develops into the pupa. The pupal stage
lasts 10 to 14 days and then the adult emerges.
The fall armyworm cannot survive the winter where the ground freezes. In the
spring, swarms of moths are blown north from the Gulf Coast and the heaviest
populations arrive from midsummer to fall. Many natural enemies attack fall
armyworm including a virus and fungal disease.
Scouting
Check for all armyworm egg masses while walking the field. Egg masses are
monitored by examining the upper and lower surface of leaves. Fall armyworm egg
masses appear similar to beet armyworm egg masses. Larvae are most difficult to
find but frequently are first found feeding on the bolls. Examine bolls for
armyworm infestation while conducting the plant inspection for other insect
pests. Classify fall armyworm eggs and larval populations according to the
classification listed below.
Eggs
None - No egg masses found.
Light - 1 to 4 egg masses
found per 56 row feet.
Medium - 5 to 20 egg masses found per 56 row feet.
Heavy -
Greater than 20 egg masses found per 56 row feet.
Larvae
None - No larvae found.
Light - 1 to 10 larvae found per
56 row feet.
Medium - 10 - 24 larvae found per 56 row feet.
Heavy - More
than 24 larvae found per 56 row feet.
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