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Agriculture Series
F@stSheet
Ent-2002
Armyworm outbreaks
are difficult to predict but infestations seem to occur in
portions of the state every year especially after early fall
rains. Common species of armyworms present in Texas include:
the fall armyworm, Spodoptera frugiperda; the yellowstriped
armyworm, Spodoptera ornithogalli; the beet armyworm,
Spodoptera exigua; and the true armyworm, Pseudaletia
unipuncta. The fall armyworm is the insect that causes
the most problems in golf courses and home landscapes.
BIOLOGY
The fall armyworm has
four life stages: egg, larva, pupa and adult. The fall armyworm
has not shown the ability to diapause so its ability to survive
winter depends on the severity of the temperature. The fall
armyworm does overwinter in the southern regions of Texas
in the pupal stage. The adult is a moth that migrates northward
as temperatures increase in the spring. Armyworm eggs and
larvae are also sometimes transported from one part of the
state to another on grass sod intended for residential and
commercial turf.
The adult fall
armyworm moth has a wingspan of about 1.5 in. The hind wings
are white; the front wings are dark gray, mottled with lighter
and darker splotched. On male moths each forewing has a noticeable
whitish spot near the extreme tip.
Eggs are very small,
white laid in clusters of 50 or more and are covered with
grayish, fuzzy scales from the body of the female moth. The
eggs are seldom seen and are laid at the base of appropriate
host plants.
Larvae hatch from
the eggs and when full-crown larvae are green, brown, or black
and about 1 to 1.5 in. long when full grown. The larva has
a dark head capsule usually marked with a pale, but distinct,
inverted "Y." Along each side of its body is a longitudinal,
black stripe, and along the middle of its back is a wider,
yellowish-gray stripe with four black dots on each segment.
The larvae have five stages or instars and usually hide in
debris on the soil surface in the middle of the day. When
full grown, larvae will enter the soil and form the pupal
stage. Adult moths emerge from pupae. Moths mate and lay eggs,
thus starting the life cycle over again. Lush plant growth
is preferred by the adults for egg laying.
Several generations
(A generation is the development from egg to adult stage.)
occur each year and typically the life cycle from egg to adult
takes 28 days. The life cycle can be extended if cooler temperatures
occur and can last up to several months. Armyworms in the
spring and summer occur in more distinct groups than later
in the season. Fall populations of larvae often blend together
several generations and may appear to be continually occurring.
DAMAGE
When feeding, larvae
strip foliage and then move to the next available food. High
populations appear to march side by side to the new food.
Thus, the name armyworms has been applied.
Armyworms attack
many different kinds of plants. When food is scarce, they
will move to plants that are not normally attacked. Thus,
armyworms can be found on nearly any plant as they migrate
in search of edible foliage. Besides warm-season turfgrasses,
plants attacked by armyworms include grain and forage sorghum,
corn, small grains, sweet potato, beans, turnip, clover, tobacco,
spinach, cucumber, potatoes, tomatoes, cowpeas, cabbage, bluegrass
and others.
Damage consists
of foliage consumption. The small larvae will chew the green
layer from the leaves and leave a clearing or "window
pane" effect. The first three instars do very little
feeding while the last two instars consume 85% of the total
foliage consumed.
CONTROL
Although armyworms
outbreaks are memorable when they occur, in reality, the outbreaks
are usually small in scope. Weather and multiple natural enemies
usually act together to keep populations under control. Parasites
such as wasps and flies are very effective against armyworms.
Predators, such as ground beetles, are also effective in limiting
outbreaks. Birds, skunks and rodents also consume large numbers
of larvae and pupae. Diseases such as insect viruses and fungi
can also be important.
Sometimes weather
conditions occur that favor armyworms. High egg survival of
fall armyworms is favored by above-average rains in August
and September. Because armyworm moths are strong fliers, outbreaks
can also occur when storms move the moths and allow them to
escape natural enemies. Armyworms should be controlled when
they occur in large numbers or plant damage is becoming excessive.
Armyworms
should be controlled when they occur in large numbers or plant
damage is becoming excessive. This will be apparent in turfgrass
by examining the grass blades. Damaged areas of lawns appear
off-color and eventually turn brown as damage progresses from
small windowpane strips of damaged leaf tissue to destruction
of entire leaves. Armyworms feed any time of the day or night,
but are most active early in the morning or late in the evening.
Treat with a labeled
insecticide when leaf damage becomes evident and large numbers
of caterpillars are visible. Effective, low-impact insecticides
include halofenozide (small caterpillars only) and spinosad.
Bacillus thuringiensis (Bt) products are
widely available and will selectively control small armyworm
larvae without harm to beneficial insects; however, Bt
residues does not last on turf for more than 1-2 days.
Conventional insecticide choices for armyworms
in lawns include bifenthrin, carbaryl, esfenvalerate, permethrin
and others.
FOR MORE INFORMATION
For more information about armyworms in agriculture,
refer to Extension fact sheet B-1220,
Managing Insect and Mite Pests of Texas Sorghum; B-1251,
Managing Insect and Mite Pests of Small Grains; B-1401,
Integrated Pest Management Guide for Texas Forage Crops.These
publications, and help with additional questions about armyworms
or other pest problems, can be obtained by contacting your
county Extension office.
Authors:
Authors:
Chris Sansone, Rick Minzemayer, John Jackman, and Mike Merchant
Extension Entomologists, Texas AgriLife Extension
Publication
information:
This publication is part of the House & Landscape Pest
Series produced by the Department of Entomology, Texas A&M
University, College Station, TX 77843-2475. The most recent
update can be found at:
http://165.95.73.17/FastSheets/Ent-2002.html
. Series Editor: M. Merchant. For more information
about arthropods, check out the Texas A&M Entomology Website
at http://insects.tamu.edu
Last revision: 10/9/01
The information given herein is for educational purposes
only. Reference to commercial products or trade names is made
with the understanding that no discrimination is intended
and no endorsement by the Texas AgriLife Extension Service is
implied. Additional, or updated copies of this fact sheet
may be obtained by contacting the author(s) at the Texas Agricultural
Extension Svc., 17360 Coit Road, Dallas, Texas 75252-6599.
Extension programs serve people of all ages regardless of
socioeconomic level, race, color, sex, religion, disability
or national origin. The Texas A&M University System, U.S.
Department of Agriculture, and the County Commissioners Courts
of Texas Cooperating.
All
content and images Copyright © 2000, Texas Agricultural
Extension Service, unless otherwise noted. All rights
reserved.
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