Research Update
=40 1990
COTTON
FIRST IN RESEARCH
UPDATE
SERIES ON COTTON
This is the first cotton re-
report published in a
s' eries, en-
.-searcth Update,"I
inaugurated in 1989 by the
Alabama Agricultural Ex-
-ernment Station. The new
series is meant to promote
timely reporting of research
results dealing with a
specific crop or commodity,
with distribution to all
producers of that particular
commodity. In this case,
the target audience is all
Alabama cotton producers.
Other information abouti
cotton production and latest
recommendations are avail-
able from each county Ex-
tension Service office in
Alabama.
Preplant 2,4-D Provides
Safe Control For Horseweed
in Minimum Till Cotton
Applying 2,4-D before planting
minimum tillage cotton gave good
control of horseweed in AAES re-
search. And there was no crop in-
jury from either 0.5- or 1.0-pound
(active ingredient) rates when ap-
plied either February 1 or March 1
ahead of late April planting. Apply-
ing the herbicide April 1 resulted in
some crop injury in one of two test
years.
Cotoran?, Prowl@, and
Gramoxone@ were used for
general weed control in the
tests conducted at the Ten-
nessee Valley and 
Wiregrass 
2,
(Headland) substations and
the Prattville Experiment
Field. A mixture of these
herbicides was sprayed on Tenr
0.5
after minimum 
tillage plant- 
1.0
ing of cotton. Plots were not
cultivated. 0.5T
Results from the Tennessee 
1.0
Valley Substation show 99
percent control of horseweed Prat
0.5
from both the 0.5-pound and 1.0
1.0-pound rates of 2,4-D ap-
Wire
plied either February 1 or 0.5
March 1 in 1987. In 1988, the 1.0
1.0-pound rate gave 99 and
98 percent control, respectively, from
the February 1 and March 1 applica-
tions. The 0.5-pound rate provided
only 70 and 83 percent control, re-
spectively, from the two application
dates.
Seed cotton yields for 1978 and
1988 at the Tennessee Valley Substa-
tion and for 1988 at the other loca-
tions are given in the table.
M. G. Patterson, W. B. Webster,
D. P. Moore, and L. W. Wells
Effect of 2,4-D Treatment on Cotton Yield
4-D/acre
Seed cotton/acre, by app. date
Feb. 1 Mar. 1 Apr. 1
Lb. Lb. Lb.
n. Valley-1987
Ib.............. 1,656
lb .............. 1,591
V. Valley-1988
lb. ................. 836
lb ............... 611
tville-1988
Ib ............... 2,398
SIb ............... 1,853
grass-1988
.Ib ................ 1,444
lb .............. 1,863
1,744
1,700
799
1,090
1,976
2,369
1,992
1,904
1,613
1,337
966
1,177
2,057
2,463
1,888
2,057
A LABAMA AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY
LOWELL T. FROBISH, DIRECTOR AUBURN UNIVERSITY, ALABAMA
I
Predators Control Beet Armyworms
in 1989 AAES Research
Beet armyworms have historically
been only sporadic pests of cotton in
Alabama. However, when outbreaks
occur, chemical control is difficult,
and damage may be severe enough
to cause a complete loss of the crop.
Infestations have become more
common in some parts of the State
during the last 2 or 3 years. In Cali-
fornia, outbreaks of beet armyworm
have been induced by insecticide
applications that destroy the preda-
tors and parasites that attack the pest,
but the reasons for outbreaks in
Alabama are unknown.
In 1989, an AAES study was be-
gun at the Wiregrass Substation,
Headland, to determine which natu-
ral mortality factors are important in
controlling beet armyworm popula-
tions in Alabama. Beet armyworm
eggs were placed either inside field
cages which excluded all predators
and parasites or inside cages that
did not exclude potential natural
control agents.
Before insecticidal applications
were made, virtually no eggs inside
cages that allowed predator access
survived until they hatched. In con-
trast, about 80 percent of the worms
that hatched in cages that excluded
all predators and parasites reached
maturity. No worms survived to
maturity when they were available
to attack by predators. Although a
diverse complex of predatory insects
was present in the field, the imported
fire ant was, by far, the most abun-
dant.
No parasites or diseases were
found in worms collected from the
field early in the season. After ma-
lathion applications (as part of the
boll weevil eradication program)
began to be made at about 5-day
intervals, predator populations de-
clined but were not completely elimi-
nated. Although beet armyworm
survival increased when predator
populations were reduced, survival
was always considerably less than
Gossym-Comax Cotton Model Promising
The Gossym-Comax cotton com-
puter model has three main uses: (1)
predicting irrigation timing, (2)
predicting nitrogen fertilizer require-
ments, and (3) predicting defolia-
tion timing. Beginningin 1987, AAES
evaluation experiments were con-
ducted to verify Gossym-Comax's
usefulness to Alabama farmers. On-
farm evaluations were conducted
with irrigated cotton in 1988 and
1989. Each year, changes have been
made in Gossym-Comax and the
1989 version was found to be signifi-
cantly improved over the earlier
years.
Based on the 3 years of evaluations,
several factors were identified for
consideration in using Gossym-
Comax:
1. Initial computer and weather
station will require a $9,000 - $10,000
investment.
2. Extensive soil water availability
measurements will be needed on
each soil type. The soil factors were
found to be a major component in
driving the Gossym-Comax model.
3. Cotton modeled with Gossym-
Comax should have access to irriga-
tion. Large periods of drought stress
have led to inaccurate predictions.
Results with irrigated cotton have
been good, especially in irrigation
timing.
4. In Alabama, Gossym-Comax
will often over-estimate cotton's
nitrogen fertilization requirement,
especially on nonirrigated cotton.
C.H. Burmester
in cages that excluded predators.
In mid-August and early Septem-
ber, a heavy flight of beet armyworm
occurred in the Wiregrass Substa-
tion fields. Despite repeated insecti-
cidal applications, predators main-
tained the wild population far be-
low those in cages that excluded
predators. Nevertheless, popula-
tions reached damaging levels in late
August. The beet armyworm out-
break was attacked by a complex of
parasites, but these parasites were
unable to significantly reduce the
pest population. Eventually, after
severe damage to the cotton, the pest
population was virtually eliminated
by a complex of fungal diseases.
Thus, predators (especially fire ants)
effectively controlled early-season
infestations of beet armyworm.
Parasites and diseases may be ef-
fective in reducing an outbreak of
beet armyworm, but probably will
not attack the infestation soon
enough to avoid crop damage.
Avoiding unnecessary early-season
insecticidal applications is advisable,
since such treatments might reduce
the effectiveness of beneficial insects.
M.J. Gaylor
Insecticide- Resistant
Aphids Controlled by
Predators
Many Alabama cotton producers
have experienced difficulty in con-
trolling cotton aphids in recent years.
The insect reproduces so rapidly that
high levels of control are required to
bring a dense population to below
damaging levels. Aphids may at-
tack cotton at any stage of plant
growth and may reduce yields. In
addition, late-season infestations
may reduce quality of the lint.
In 1988, when many growers had
great difficulty in controlling aphids,
cotton aphids collected from several
parts of Alabama were found to have
developed high levels of resistance
to a wide range of insecticides.
I I _ I--
Resistance levels increased rapidly
with additional insecticidal applica-
tions. For example, in a population
from Tallassee, resistance to an or-
ganophosphorus insecticide in-
creased from about 15-fold to 40-
fold following a single application
of the insecticide.
For the first time in several years,
few control failures were reported
in Alabama in 1989. Concurrently,
little insecticidal resistance was de-
tected. Reasons for the absence of
resistance in 1989 are unknown, 
but
probably are related to fewer insec-
ticidal applications in early and mid-
season. Also, heavy spring rains
provided ideal conditions for infec-
tionby fungal diseases and may have
washed many aphids from the
plants. The fungal diseases had vir-
tually eliminated the aphids by late
August.
A study at the Tennessee Valley
Substation, Belle Mina, demon-
strated the need to avoid insecticidal
Aphids/leaf, no.
50 1 - Fungi-infected 
aphids
40 -
SCypermethrin
- - Sulprofos
. heck
0 I L -1
Parasitized aphids \
2.0 ,
1.5
1.0 /
0.5
o F I I 1
Cotton aphids
75 I
50 -
25- - " "
June26 July18 July31 Aug.15 Aug.28
applications until they were neces-
sary. In plots where no insecticides
were applied, predatory insects
maintained relatively good control
of aphids throughout the season.
Aphid populations also remained
low in plots treated with the syn-
thetic pyrethroid cypermethrin, see
figure. In contrast, aphid popula-
tions reached extremely high levels
in plots treated with the organo-
phosphorus insecticide sulprofos.
Reasons for the differences in the
cypermethrin- and sulprofos-treated
plots are unknown. Predator popu-
lations were similar in the two treat-
ments, and there were few differ-
ences in insecticide-induced aphid
mortality. Fungal diseases eventu-
ally controlled the aphid outbreak,
but not until the pest populations
had reached unacceptably high
densities. Parasites also attacked
the aphids in these plots, but were
not an important factor in bringing
the outbreak under control.
M J. Gaylor
Narrow-Row Cotton
Yields Higher Than
Standard Row-Width
Cotton
Interest in narrow-row cotton is
increasing across the Cotton Belt.
Growers in some areas have reported
higher yields from 30-inch rows than
in standard, wider rows. Cotton
pickers are now available which can
harvest cotton grown in 30-inch
rows.
AAES research was begun in 1989
to investigate the effect of row spac-
ings, Pix? plant growth regulator,
and weed control requirements on
cotton yield at the Tennessee Valley
Substation, Belle Mina, and Prattville
Experiment Field, Prattville. Varie-
ties used were DPL 50 at Belle Mina
and DPL 90 at Prattville, planted in
solid 30-inch and 40-inch rows and
in skip row 40-inch rows. Two ap-
plications of Pix at 8 fluid ounces per
Yield Per Acre at Different Row Spacings
Seed cotton yield/acre
Row spacing Belle Mina Prattville Av
Lb. Lb. Lb.
Solid 30-in ........... 2,516 2,135 2,325
Solid 40-in ........... 2,460 1,933 2,197
Skip 40-in ............ 2,057 1,730 1,894
acre were applied to all row-spacing
treatments.
Yields were highest for the solid
30-inch row plantings when aver-
aged across weed control and Pix
treatments at both locations, as
shown by data in the table. The Pix
applications provided no benefit to
cotton in any row width. 
Likewise,
low or high weed control levels did
not affect yield in any row spacing.
M G. Patterson
K Fertilization
Increases Yield
of Cotton Following
Alfalfa
Seed cotton yields were increased
by applying potassium (K) fertilizer
to a field that had previously been in
long-term alfalfa production. The
same potassium rates had been
applied for 3 years preceding alfalfa
in the field plots at the Tennessee
Valley Substation, Belle Mina.
Stoneville 825 and Deltapine 50 cot-
ton varieties were compared in the
tests.
Cotton yields were not affected by
K fertilization the first year (1987) of
the test. Small yield increases re-
sulted from K application the sec-
ond year (1988). Stoneville 825
yielded 1,616 pounds of seed cotton
per acre that year, compared with
1,436 pounds for Deltapine 50.
Greatest yield responses to K fer-
tilizer occurred in 1989, as shown by
data in the table. Applying 60 pounds
K20 per acre each of the 3 years
(1987,1988, and 1989) increased seed
Yield Response to Potassium by Cotton
Following Alfalfa
Pounds K
2
0/acre/year 
Tot
Fall' Spring
2
Total 19
'Broadcast
'Broadcast
al KO, Seed cotton/
87-89 acre, 1989
Lb. Lb.
0 1,777
180 2,649
J zu 360 Z,014
D 180 540 2,942
D 120 360 2,860
D 180 540 2,840
D 120 360 2,740
and plowed down.
prior to planting.
cotton yields 872 pounds per acre
over production with no K applied.
Using higher rates of K or splitting K
applications between spring and fall
did not increase yields over the 60-
pound rate applied in spring. Del-
tapine 50 outyielded Stoneville 825
in 1989-2,814 vs. 2,507 pounds seed
cotton per acre.
Results from this study suggest
that more than 1 year of K applica-
tion may be necessary to achieve top
yields of cotton following long-term
forage production.
G.L. Mullins and C.H. Burmester
EDITOR'S NOTE
Mention of company or trade names
does not indicate endorsement by the
Alabama Agricultural Experiment
Station or Auburn University of one
brand over another. Any mention of
non-label uses or applications in
excess of labeled rates of pesticides or
other chemicals does not constitute a
recommendation. Such use in re-
search is simply part of the scientific
investigation necessary to fully evalu-
ate materials and treatments.
Information contained herein is
available to all persons without regard
to race, color, sex, or national origin.
S U P PTOC. ToRT C, TT0 N 
R ES E A C H-
i unds appropriated by the Alabama Legislature 
provide the major fi-
nancial support for Alabama Agricultural FxperimentStationresearch.
Hatch :::funds from the U.S. Government also represent 
an important
funding source. Since these funds are iimited, 
however, many areas of
researc!h would go unsuIpported except for financial 
support from vari-
ous granting agencies, commodity groups, and other 
friends of the I x-
periment Station. Among these supporters of 
AAES research, the
following are recognized and thanked for their 
contributions to re-
search on cotton production:
Agrogenetics Co., Ltd.
Alabama Cotton Commission, AL 
:::::::
Ciba-Geigy Chem ical 
Co.
Ecogen, Inc.
Fluid Fertilizer Foundation
Gustafson
ICI Americas Chemical Co.
Nor-Am Chemical Co.
Pennwalt Corp.
Ten:n ssee Valley Authority
Uniroyal Chemical Co.
LU' " I .. .- Assessment Program
Alabama Agricultural Experiment Station
Auburn University
Auburn University, Alabama 36849-0520
NON-PROFIT ORG.
POSTAGE & FEES PAID
PERMIT No. 9
AUBURN, ALA.
April 1990 5M II