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Beet Armyworm
BIOLOGY AND CONTROL
MAX H. BASS, PATRICIA POWELL COBB, and DAN HIGGINS*
LEAFLET 94 JUNE 1978
DURING THE LAST several years, 
the
beet armyworm, Spodoptera exigua
(Hubner), has become a pest on several
economic crops in Alabama. Reports on
*Respectively, Professor, Department of
Zoology-Entomology: former research assis-
tant, Department of Zoology-Entomology,
now Extension Entomologist, Alabama
Cooperative Extension Service; and former
research assistant, Department of Zoology-En-
tomology, now Insecticide and Nematicide
Product Manager, Chemagro Chemical Cor-
poration.
chemical control research emanating
from the southeastern and southwestern
regions of the United States indicate
differences in chemical susceptibility bet-
ween the strains found in these two areas.
Research by the Auburn University
Agricultural Experiment Station demon-
Different stages of beet armyworm are
shown in the title illustration: Egg mass
hatching (lower left); larva, side and dorsal
view (right); pupa (left center); and adult
(left top).
AGRICULTURAL EXPERIMENT STATION / AUBURN UNIVERSITY
R. DENNIS ROUSE, Director AUBURN, ALABAMA
a
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~a~i~891~es14L, __ _~
strated insecticidal resistance in the
southeastern strain to several commonly
used insecticides.' Further field research
was conducted at Auburn to determine
the biology of the insect and to establish
field control techniques.
BIOLOGY
A native of the Orient, the beet ar-
myworm was first detected in the United
States as a pest of sugar beets (hence the
name) in Oregon late in the 19th century.
2
By the 1920's this insect was present in the
Southeast
3 
where it has caused sporadic
problems since that time. Since 1966 the
authors have observed increasingly
severe, although still sporadic, damage
from this pest. Some of the more impor-
tant hosts in Alabama are peanuts, soy-
beans, cotton, corn, forage legumes, and
pasture grasses.
The egg of the beet armyworm is ribbed
and nearly spheroid. It is greenish-gray
when freshly laid, becomes cream colored
within a few hours, and later darkens as
the developing black larval head becomes
more prominent. Under field conditions
in Alabama the egg hatches in 3-4 days.
The newly hatched larva is light green,
about a millimeter long, and has a rela-
tively large, dark head. The larva molts as
it passes from instar to instar and becomes
progressively larger until the last instar is
about an inch long. Larval color is incon-
sistent and varies from light green to
pinkish gray to almost black. Past the
third instar the head is brown. Field iden-
tification is facilitated by the presence of a
dark spot on each side of the thorax just
above the middle leg. The larva has five or
six instars and the larval period lasts from
15 to 25 days in the field. The length of
time required for larval development
decreases at higher temperatures.
Pupation occurs in the ground. The lar-
'COBB, PATRICIA POWELL AND MAX H. BASS.
1975. Beet Armyworm: Dosage-mortality
Studies on California and Florida Strains. J.
Econ. Entomol. 68(6):813-814.
2
HARVEY, L. F. 1976. New California and
Texas Moths. Canadian Entomologist 8:54.
3
WILSON, J. W. 1932. Notes on the Biology of
Laphygma exigua Huebner. Florida Entomologist
16(3):33-39.
va bores into the ground at the end of the
larval period and constructs a pupal cell
about 1 inch below the surface. The pupa
is about 5/8 inch long and is light green
when newly formed. It gradually turns
brown, becoming dark brown at maturity.
The pupal stage lasts 6 or 7 days, after
which the adult emerges. Egg to adult de-
velopment is usually completed in about 3
weeks.
The adults are gray to gray-brown
moths with a wing expanse of 3/4 to 1
inch. The forewings are mottled gray with
a light spot near the center of each. The
hindwings are lighter in color than the
forewings but have a dark border near the
edges. Almost all adult activity takes
place at night. Adults usually emerge at
night, mate within 24 hours, and begin
laying eggs within 48 hours. The moths
deposit eggs over about a 5-day period
and lay about 500 eggs in clusters of
50-150, usually on the undersides of
leaves of host plants. The egg clusters are
covered with scales from the female's
body and appear "fuzzy."
CONTROL EXPERIMENTS
Procedures
Insecticides were evaluated for effec-
tiveness against the beet armyworm in
Coffee County, Alabama. An infestation
of approximately 11 worms per foot of
row was found in peanuts in early July.
Three experiments were conducted: the
first on July 9, the second on July 13, and
the third on August 11. In each case, 10 or
11 treatments (9 or 10 insecticidal treat-
ments and a check) were used. All treat-
ments were replicated four times in a ran-
domized block design.
The following insecticides were evalu-
ated in one or more of the experiments:
methomyl (Lannate? or Nudrin?), metha-
midophos (Monitor?), monocrotophos
(Azodrin?), trichlorfon (Dylox? or Prox-
ol?), carbofuran (Furadan?), azinphos-
methyl (Guthion?), tetrachlorvinphos
(Gardona?), Bacillus thuringiensis (Thuri-
cide? or Dipel?), Pyrellin?, fonofos
(Dyfonate?), SD-17250, N-2596,
temephos (Bithion?), diazinon, dimetho-
ate (Cygon?), dicofol (Kelthane?),
TABLE 1. BEET ARMYWORM CONTROL ON PEANUTS, EXPERIMENT 1, COFFEE COUNTY, ALABAMA
1 day after treatment 
4 days after treatment
ingredient/acre 
No. live Percent No. 
live Percent
larvae
1  
control larvae
1  
control
Methomyl 1.8 L, 1 pound ............... 0.3 98 0.4 98
Methamidophos 4 EC, 1 pound .......... 1.9 83 2.2 86
Monocrotophos 5 EC, 1 pound .......... 6.2 45 8.8 44
Trichlorfon 4 EC, 2 pounds ............. 6.2 45 9.4 40
Carbofuran 4 F, 1 pound ................ 10.1 10 14.2 10
Tetrachlorvinphos 4 EC, 1 pound ........ 11.4 0 15.3 3
Azinphosmethyl 2 EC, 1 pound .......... 11.0 2 16.2 0
Pyrellin?,
2 
1 quart...................... 12.2 0 17.4 0
Thuricide?,
3  
1 quart .................... 11.9 0 17.4 0
Fonofos 4 EC, 2 pounds ................ 13.3 0 19.9 0
Check................................. 11.2 - 15.8 -
'Mean number of live larvae per row foot (9 row feet sampled per plot, each treatment replicated four times).
20.6 percent pyrethrins, 0.5 percent 
rotenone.
3
Bacillus thuringiensis.
phosphamidon, and malathion. All ap-
plication rates are given as amount of ac-
tive ingredient per acre.
Most materials were applied as sprays
in a 12-inch band over the row using 2-
gallon, hand sprayers delivering 12.5
gallons of insecticidal spray per acre.
Baits were applied by hand in a 12-inch
band over the row. Data were taken from
the middle two rows. Counts of both live
and dead beet armyworms were made in
the following manner: A 3-foot section of
row was randomly selected. The peanut
plants were vigorously shaken to dislodge
beet armyworm larvae. The plants were
rolled back from the middles to the row
on one side of the row and the number of
live and dead larvae was determined and
recorded. This procedure was repeated
on the other side of the row so that all live
and dead worms dislodged in this 3-foot
section were counted. This entire pro-
cedure was repeated three times in each
plot so that a total of 9 feet of row was
sampled.
The economic injury threshold, based
on number of larvae per foot of row, has
not been established for the beet ar-
myworm. For determining adequate
effectiveness of materials, however, many
researchers have used 80 percent control
as an acceptable level. This minimum
level of control was used in evaluating
materials in the experiments reported
here.
RESULTS
In experiment 1, beet armyworm
populations were sampled 1 day and 4
days after the application of insecticides,
table 1. One day after treatment only
methomyl and methamidophos (both at 1
pound per acre) reduced beet armyworm
TABLE 2. BEET ARMYWORM CONTROL ON PEANUTS, EXPERIMENT 2, COFFEE COUNTY, ALABAMA
1 day after treatment 3 days after treatment
ingreatment active No. live Percent No. live Percent
ingredient/acre larvae control larvae control
Methomyl 90 SP, 1 pound ................ 0.4 91 0.5 90
Methomyl 1.8 L, 0.5 pound ............. .3 93 .5 90
Methomyl 90 SP, 0.5 pound .............. .4 91 .6 89
Methamidophos 4 EC, 1.5 pounds ....... .6 87 1.0 83
Trichlorfon 4% bait, 1 pound ........... 1.9 55 2.4 57
Thuricide?,
2 
2 quarts ................... 3.9 6 3.5 38
SD-17250 5 WP, 1 pound ................ 3.1 26 3.9 31
N-2596 4 E, 1 pound ................... . 3.8 10 5.2 8
Temephos 50 WP, 1 pound ............... 4.7 0 5.6 0
Check ................................. 4.2 - 5.6 -
'Mean number of live larvae per row foot (9 row feet sampled per plot, each treatment replicated four times).
2
Bacillus thuringiensis.
populations by 80 percent or more. At 4
days post-treatment, again, the applica-
tion of both methomyl and methamido-
phos at the 1-pound rate resulted in
population reductions greater than 80
percent. The application of some of the
remaining insecticides tested produced
population reductions, but none ap-
proached 80 percent.
Experiment 2 included the materials
that had been effective in experiment 1,
(methomyl and methamidophos), but
materials which had not been effective
were dropped and replaced with pre-
viously untested compounds. Methomyl
90 SP at 1.0 and 0.5 pound per acre,
methomyl 1.8L at 0.5 pound, and meth-
amidophos 4E at 1.5 pounds all reduced
populations by more than 80 percent 24
hours after treatment, table 2. No other
materials afforded acceptable control.
Data taken 3 days after treatment are also
presented. The same pattern seen in table
1 is repeated. All rates and formulations
of methomyl and methamidophos pro-
vided acceptable control. Other materials
tested were considerably less effective.
Table 3 presents data from experiment
3. In this experiment, various formula-
tions and rates of methomyl along with
several previously untested materials were
used. Data were collected at 24 hours
only. A 2 percent methomyl bait used at
the rate of 1 pound per acre afforded
good control, as did 1/2 pound per acre of
TABLE 3. BEET ARMYWORM CONTROL ON
PEANUTS 1 DAY AFTER 
TREATMENT,
EXPERIMENT 3, COFFEE
COUNTY, ALABAMA
Treatment, active No. live Percent
ingredient/acre larvae
1  
control
Methomyl 90 SP, 0.5 lb.. 0 100
Methomyl 1.8 L, 0.5 lb... 0 100
Methomyl 2% bait, 1 lb. 0 100
Methomyl 1.8 L, 0.25 lb.. 1.0 86
Methomyl 90 SP, 0.25 lb. 1.8 76
Diazinon 4 EC, 2 lb ...... 5.8 23
Dimethoate 1.67 EC, 1 lb 6.2 17
Dicofol 1.6 EC, lb .....
6.5 13
Phosphamidon 8 S, 1 lb. 6.9 8
Malathion 4 EC, 1 lb..... 7.5 0
Check .... ............ 7.5
'Mean number of live larvae per row-foot (9 row
feet sampled per plot, each treatment replicated four
times).
methomyl 90SP and methomyl 1.8 L. The
1/4-pound rate of methomyl provided ac-
ceptable control in one case but not in
another. No other treatments resulted in
acceptable population reduction.
SUMMARY
The use of methomyl 90 SP and
methomyl 1.8 L at rates as low as 0.5
pound active ingredient per acre and the
use of methamidophos 4 EC at 1 to 1.5
pounds provided consistently acceptable
control of the beet armyworm in this
series of tests. None of the other 17
materials tested provided acceptable con-
trol.
Information contained herein is available to all without regard to race, color, or national origin.