Pest Information: Armyworms
Armyworms are stout-bodied, hairless,
striped caterpillars that chew the foliage of grasses and grain crops.
They are so named because of their habit of crawling in large numbers
from field to field when they have exhausted their food supply. Several
specie of armyworms may attack turfgrasses. Homeowners and golf course
superintendents are understandably concerned when their turf is
literally mowed down by a mowing “army” of caterpillars that seems to
appear overnight. These pests are sporadic, but have an ever-present
potential for outbreaks.
There are three major species of armyworms that attach turf in the United States. “True” armyworm (Pseudaletia unipuncta), Fall armyworm (Spodoptera frugiperda), and lawn armyworm (Spodoptera mauritia).
“True” armyworms are especially fond of corn and small grains but will
feed on all common turfgrasses. This specie probably does not
over-winter in the Northern half of the United States but annual
infestations in the middle and northern parts of the United States
result from the northward migrations of moths in the spring. These
armyworms are gregarious and tend to feed as a group, devouring
circular patches of turf before moving on to another food soucre. They
tend to hide in the thatch during the day and most of the damage occurs
Fall armyworms are similar to “True”
armyworms but the damage they cause is more uniform over a broader
area. These insects feed anytime during the day or night but move about
mostly in the dark or early morning.
Lawn Armyworm is a major pest of bermuda grass in Hawaii. The injury is similar to that caused by the “true” and fall armyworm.
Adult “true” armyworms are uniformly
pale-brown to grayish brown with a wingspan of about 1.5 in. Adult fall
armyworms and lawn armyworms are the same size as “true” armyworms but
are dark gray. Adult moths generally remain hidden by day but become
more active at night and are attracted to light. Newly hatched larvae
are greenish, and older ones are 1.5 in. long and range in color from
light tan to olive green to nearly black, and have stripes along the
sides of their back. Fall army worms can be distinguished from true
armyworms by the more prominent inverted Y- shaped marking on the front
of the head and the presence of 4 distinct black tubercles on the back
of each abdominal segment.