The fall armyworm is a sporadic
but serious pest of turfgrasses in North Carolina. The larva is the damaging
stage of this pest and it is 1 inch to 1½ inches long when fully grown. It can
vary in color from green to brown, to almost black. There are four black dots
on the dorsal side of each abdominal segment. It has a distinct inverted “Y” on
the head. The true armyworm is similar in appearance but lacks the inverted
“Y.” The moth has a wingspan of about 1 to 1½ inches. The hind wings are white;
the front wings are dark gray, mottled with lighter and darker splotches. Each
forewing has a noticeable whitish spot near the extreme tip. The eggs are very
small and laid in clusters of 50-250. Egg clusters are fuzzy patches covered
with scales from the female moth and resemble cotton. The mass is greenish
white but turns darker prior to hatching. The pupa, approximately 1.2 inches
long, is somewhat football shaped. It is reddish-brown at first, and darkens to
black as it matures.
General
Information
The fall armyworm has been a pest
of turfgrass in North Carolina for many years. However, its occurrence and the
resulting damage appear to have increased since 1995. As a result it has become
a major concern for turfgrass managers throughout the Carolinas in both cool
and warm season turfgrass.
The fall armyworm does not
overwinter in North Carolina, but egg-laying armyworm moths migrate northward
from Florida and the Gulf Coast areas throughout the spring and summer and
begin to arrive in North Carolina in June. New moths may continue to appear
into November. Each female lays about 1,000 eggs in masses of 50 or more. Two
to 10 days later the small larvae emerge, feed on the remains of the egg mass,
then scatter in search of food. After feeding for 2 to 3 weeks, the larvae dig
about 0.8 inches into the ground to pupate. Within 2 weeks, a new population of
moths emerges and usually flies several miles before laying eggs. It is possible
that in some years we may have as many as 4 generations of fall armyworms in
North Carolina.
Damage
The fall armyworm feeds on a wide
range of plants, but prefers grasses. Damage to bermudagrass in the southern
U.S. is most common, but fescue, ryegrass, bentgrass, and bluegrass are also
attacked. Lush, green turfgrass is the most frequently attacked host.
Fall armyworm caterpillars feed
only above the ground on the foliage of the turf. Larger larvae often consume most
of the leaf tissue and in the case of bermudagrass, the turf often takes on the
appearance that it has been subject to frost. The damage often begins along one
edge of the turf area and moves across. Bermudagrass usually recovers from such
damage, but feeding late in the fall may stress the turf going into the winter
and result in some winterkill. Cool season turfgrass can be permanently damaged
if the growing tips are destroyed.
When numerous, this insect will
devour grasses down to the ground, causing circular bare areas. Some years the
fall armyworm is a serious pest of turfgrasses in North Carolina, usually
following cool, wet springs which seem to reduce the effectiveness of naturally
occurring parasites. Fall armyworms feed any time of day or night, but they are
most active early in the morning or late in the evening. When abundant, fall
armyworms eat all available food and move in mass to adjoining areas. The
larvae feed two to three weeks and a generation takes about five to six weeks.
Several generations occur each year. The fall armyworm is a common pest of
newly seeded stands of cool-season turf in the fall and often attacks
overseeded areas of warm-season grass as the ryegrass establishes.
Scouting
and Early Warnings
Discolored turfgrass is often the
first sign of fall armyworms. The damage often begins along one edge of the
turf area. Large numbers of birds in a turf area may well be a sign of fall
armyworms and the presence of food for the birds. Green, fecal pellets can
often be seen in areas of damage. The use of soapy water flush to bring fall
armyworms to the surface can be a valuable time-saving tool to detect the
caterpillars prior to severe damage to the turf. The soapy water flush consists
of two tablespoons of liquid dishwashing detergent mixed in two gallons of
water. Slowly pour from a bucket or sprinkling can the whole contents onto
approximately a square yard (3 ft X 3 ft) area and then observe closely over
the next few minutes for the fall armyworms (and any other caterpillars
present) scrambling to the top of the turfgrass. It is not uncommon for the
turf to be severely damaged and by the time someone begins looking for
caterpillars, they have already entered the soil to for a pupa.
Treatment of established turf is
not necessary on a frequent or widespread basis. However, there are three
situations that are often the targets of armyworm infestations and suffer
severe damage. Any turf setting that contains new, lush turf growth and is
receiving a lot of water and fertilizer is a prime target for an infestation.
Newly seeded areas are often attacked late in the summer or early fall.
Sprigged areas also come under frequent attack from this pest and establishment
can be seriously impacted. In recent years, the most common report of fall
armyworm has been associated with areas of new sod. The common scenario is that
the sod is laid on site, watered and after a couple of weeks it begins to turn
brown. More water and fertilizer is applied, but the turfgrass continues to
decline. Finally someone checks for armyworms and either finds large
caterpillars or nothing at all. In many situations, the caterpillars will not
be found because they are pupae in the soil.
One important consideration to
keep in mind when sod is placed at any site is that most infestations probably
originate at that site. Remember that the eggs are not commonly laid on the
turf, but on objects nearby. Any infestation that begins to show up several
weeks after the sod was laid most likely was the result of caterpillars moving
into the area after they hatched from adjacent areas. This is not to say that
it is impossible for fall armyworms to come in with the sod, but rather to help
producers and buyers alike, understand that most problems originate on site. If
fall armyworm damage occurs within two weeks of the time the sod was purchased,
then it is possible that small worms came in with the sod. However, even in
that scenario, it is possible that medium sized fall armyworms were present in
surrounding areas and immediately migrated to the new sod. These caterpillars
are called "armyworms" because they do indeed "march" to
the best available food source.
Control
Practices
The fall armyworm is more
difficult to control chemically than the true armyworm. Control of fall
armyworms will be improved if you cut the turf prior to treating. A light
irrigation prior to treatment may also help as will treating late in the day.
Chemical control is needed if natural enemies do not keep infestations below
the economic threshold of 1 per square foot on general turf or 1 per square
yard on golf greens. If possible, do not mow turf and remove clippings for
several days after treating for any of the caterpillar pests.
Large fall armyworms are
difficult to control. Don't expect 90% control. If the worms are very large
(inch and a half long) then they will go into the soil very soon to pupate and
control efforts may be ineffective. Timing is important and a repeat
application may be necessary in some situations. For specific control
information, consult the NC Cooperative Extension Service recommendations (Pest
Control for Professional Turfgrass Managers 2007).