L.EAFLET 77
SEPT EMBER 1968
p (9)
Effect of paraquat on immature
boils is illustrated by this comn-
porison. Boils in the two upper
rows were treated with DEF+
paraquat, 1 pint of each per
acre. Those in the lower row
ore from cotton treated with
1 1/2 pints per acre DEF alone.
DEFOLIATION, DESICCATION, AND
REGROWTH INHIBITION
OF COTTON
G. A. BUCHANAN, Assistant Professor of Agronomy and Soils
EM. EVANS, Associate Professor of Agronomy and Soils
W. T. DUMAS, Associate Professor of Agricultural Engineering
U liit IIA Lx-l x) (llettili(,ills lot cot-
chit 11lla thle pastI f('\v \(ai. Somle '3( [to 4(0
prcetit ofl tile StateIs elitp wxas treated
xx iti detoliatsI ill 19(6?. \l1c otel this fli]
ceas~ie eamie ablout 1heeattxe of almtost
tcmplete 111(111 iitiatiitt ofii hat Ne('til ii
Mtid tise of i(Thiet lexvels of lltoztel tter
I ili/at jolt
Despite xxdcespe ad usce of ~- defolan ts
axs ptehltxest elliek~ls, thtere is muceh
co~sol ii as ti \\ hat ttex v lshtuld (to.
cilpoif)lltedl ill the resutltx. Dl~eolialtit
the prioess. lTtts, [lth e tlVlttte tffleetix
xx iit't applied to loittt i cottitt that i
60I to 8I0 })( cett)1 lpell \\,]tx lell tem-t
petatttrex ate high aiid tittire is lowx
it tilei of app] ic ,lttttt IfI)('\e\- gi oxxtl is
sligh t, tetolp~tt itIt high, atl ci axailihie
0ttil toixttit t lo\ix, a tielotilit stiell ax
dotes a xatixltotx jt)b lt
1
d Itilitatexs
it N (xl.
I'Mte phlittgx, e'\texxlx\( l lat h' ttjtt i
A GR IC UL TU R AL 6 X P ERI M ENT S T ATIO N
AUBURN UNIVERSITY
E. V. Smith, Director Aubun. Alabama
tures, and excessive rainfall result in de-
layed maturity and slow opening. Under
such conditions in 1966 and 1967, cotton
continued to grow vigorously until frost.
This situation increases interest in har-
vest-aid chemicals that will desiccate the
new growth and prevent regrowth, as
well as defoliate the plants.
Early work by Hall' indicated that
amitrole (3-amino-1,2,4-triazole) was an
effective defoliant and had some re-
growth inhibiting properties. Hogue and
Frans
2 
later reported that both amitrole
and pyriclor inhibited regrowth of cotton
for 5 to 6 weeks after application. In
mixtures with DEF, both pyriclor and
amitrole reduced regrowth when com-
pared to DEF alone.
Hogue and Frans also reported that
addition of endothall (7-oxabicyclo 2.2.1
heptane-2, 3-dicarboxylic acid) to DEF
increased desiccation over DEF alone.
When endothall was added to Folex,
however, defoliation was increased over
that of Folex alone but there was no in-
crease in desiccation. Paraquat (1,1'-
dimethyl-4, 4-bypridinium salt) added to
DEF significantly increased desiccation,
but regrowth was not inhibited.
Studies were begun by Auburn Uni-
versity Agricultural Experiment Station
in 1967 to determine the effect of endo-
thall, paraquat, and pyriclor on defolia-
tion, desiccation, regrowth inhibition, and
injury to cotton when applied in combi-
nation with DEF.
DESCRIPTION OF EXPERIMENTS
Field studies during 1967 at the Agri-
cultural Engineering Research Unit at
Marvyn, Alabama, were made to eval-
uate combinations of paraquat or pyriclor
1 HALL, W. C., S. P. JOHNSON, AND C. L.
LEINWEBER. 1954. Amino Triazole-A New
Abscission Chemical and Growth Inhibitor.
Tex. Agr. Exp. Sta. Bull. 789.
2 HOGUE, CHARLES W. AND 
R. E. FRANS.
1967. Use of Chemical Combinations for
Defoliation, Desiccation, and Regrowth In-
hibition Prior to Cotton Harvest. Proc. An-
nual Cotton Defoliation and Physiology Con-
ferences 21:84-87.
with DEF. One experiment consisted of
five treatments in plots 8 rows wide and
100 feet long. Treatments were repli-
cated three times in a randomized com-
plete block design.
The plots were planted to Auburn 56
variety on April 26 and subjected to
Sstandard production practices during the
growing season. All chemicals were ap-
plied September 21, using a high-clear-
ance sprayer with one K-5 flooding noz-
zle mounted on the spray boom directly
above each row, in 20 gallons of water
per acre. The cotton was approximately
TABLE 1. DAILY RAINFALL FOR JULY-
OCTOBER 1967, MARVYN RESEARCH
UNIT
Rainfall by days
Date July 
Aug. Sept. 
Oct.
In. In. In. In.
1 0.70
2 ---------- 0.30
3 -------- 2.00 2.40
5
3de t F l ------------------
6 0.75
7 -- 2.20 0.17 0.85
8 0.15 0.10
9 0.20
10-
i __ :---- ---- ----
11 1.20
12 ----------.
13 -------------- 0.40
14 0.25
15 -
16
17 -0.10
1 8 --- - --- ---
19 --------- 0.50
2 0 -- ------
21 0.35
22 0.40
23 --------- 0.40
24 - 0.28 1.15
25 0.30 0.95
26 --------- 1.15
2 7 -----------------
28 --------- 0.05
2 9 -- ------
80
31 2.00
[2]
3 feet tall and 60 to 70 per cent open at
time of application. Rainfall during the
study period is recorded in Table 1.
Leaf drop, regrowth, and immature
boll injury estimates were made October
2, 6, and 10. On October 24, seed cotton
yield and harvesting efficiency were de-
termined for each treatment. At harvest,
regrowth from a portion of one row in
each plot was harvested, dried, and
weighed. Unopened bolls were also har-
vested and the amount of cotton remain-
ing in these bolls determined.
In a second experiment at the Marvyn
Research Unit, application was made
when only 40 to 50 per cent of the cot-
ton bolls had opened. Treatments were
applied as described in the previous ex-
periment on October 2.
An additional experiment was begun
September 11, 1967, at the Agronomy
Farm, Auburn. Experimental methods
were the same as previously described,
except endothall was included as a treat-
ment.
RESULTS OF MARVYN EXPERIMENTS
Fifteen days after treating (October'
6), cotton treated with 11/2 pints per
TABLE 2. EFFECT OF PARAQUAT AND
PYRICLOR IN COMBINATION WITH DEF
ON LEAF DROP OF COTTON, MARVYN
RESEARCH UNIT, 1967
Chemical and
Leaf drop'
per acre rate Oct. 2 Oct. 6 Oct. 10
Pct. Pct. Pct.
DEF, 11/ pt. 83 a 93 a 90 ab
DEF, 1 pt. +
paraquat, / 
pt. 78 a 
80 b 82 b
DEF, 1 pt. +
paraquat, I pt.-. 72a 73b 70 b
DEF, 1 pt. +
pyriclor, 2 pt... 87 a 90 a 95 a
DEF, 1pt. +
pyriclor, 3 pt. 77 a 85 ab 93 a
1When values within columns are fol-
lowed by the same letter there is no differ-
ence because of treatment, as figured by
standard statistical methods; those followed
by different letters differ significantly.
acre of DEF had dropped 93 per cent
of its leaves, Table 2.
When either 2 or 3 pints per acre of
pyriclor was applied with DEF, defolia-
tion remained about the same. With
paraquat in the spray solution there was
a slight reduction in leaf drop at the 1/2
pint per acre rate ind a substantial re-
duction when 1 pint per acre was used.
The reduced leaf drop at the higher rate
of paraquat was caused by "leaf freez-
ing."
TABLE 3. EFFECT OF PARAQUAT AND
PYRICLOR IN COMBINATION WITH DEF
ON BURN OF UNOPENED BOLLS,
MARVYN RESEARCH'UNIT, 1967
Unopened 
bolls
Chemical and having some burn'
per acre rate
Oct. 2 Oct. 10
Pct. Pct.
DEF, 11/
2
pt. Oa 0 a
DEF, 1 pt. +
paraquat, 1/ pt. 80 b 80 b
DEF, 1 pt. +
paraquat, 1 pt. 83 b 82 b
DEF, 1 pt. +
pyriclor, 2 pt. a 4a
DEF, 1 pt. +
pyriclor, 3 pt.O 0a 
4 a
1 When values within columns are fol-
lowed by the same letter there is no differ-
ence because of treatment, as figured by
standard statistical methods; those followed
by different letters differ significantly.
No injury to immature unopened bolls
was observed in plots treated with DEF
alone at 1 pints per acre, Table 3. Ad-
dition of pyriclor at rates up to 3 pints
per acre caused no significant injury.
Few of the immature bolls showed any
detectable burn. The addition of para-
quat at 1/2 pint per acre to DEF caused
severe burn to as high as 80 per cent of
the unopened bolls. Type of burn ob-
served on unopened bolls is shown in the
title photograph.
The number of cotton plants initiating
regrowth was not affected by addition
of paraquat to the spray solution, Table
4. However, regrowth on plots treated
with 1 pint DEF and 2 or 3 pints pyri-
[8]
TABLE 4. EFFECT OF PARAQUAT AND
PYRICLOR IN COMBINATION WITH DEF
ON REGROWTH OF COTTON, MARVYN
RESEARCH UNIT, 1967
Chemical and
per acre rate
Plants initiating Regrowth
regrowth' per acre,
1
Oct. 2 Oct. 
10 Oct. 24
Pct. Pct. Lb.
DEF, 1/
2
pt.. 15 a 18 a 29 a
DEF, 1 pt. +-
paraquat, 1/2 pt. 8 ab 13 a 25 a
DEF, 1 pt. +
paraquat, 1 pt.__ 6 ab 18 a 28 a
DEF, 1 pt. +
pyriclor, 2 pt--. Ob 2 b 6 b
DEF, 1 pt. ?
pyriclor,.3 pt.-- 0 b 2b 6b
1 When values within columns are fol-
lowed by the same letter there is no differ-
ence because of treatment, as figured by
standard statistical methods; those followed
by different letters differ significantly.
clor per acre made only approximately
25 per cent as much regrowth as did cot-
ton treated with 1 /2pints per acre DEF.
Although only slight regrowth occurred
in this experiment, the potential was evi-
dent and could be substantial under high
moisture and fertility conditions.
Yield of cotton was not significantly
reduced in any treatment, Table 5. There
was, however, a significant increase in
amount of cotton remaining in unopened
bolls when treated with DEF + para-
quat (1 pint each per acre). Picking ef-
ficiency was reduced slightly. Adding
pyriclor to the spray solution did not re-
duce yields or decrease picking efficiency
when compared with DEF treatment
alone. Amount of cotton remaining in
unopened bolls when treated with pyri-
clor was comparable to that in cotton
treated with DEF alone.
TABLE 5. EFFECT OF PARAQUAT AND PYRICLOR IN COMBINATION WITH DEF ON YIELD OF
PICKER-HARVESTED COTTON, UNOPENED BOLLS, AND PICKER EFFICIENCY,
MARVYN RESEARCH UNIT, 1967
Chemical and per acre rate
D E F , 11/2 pt. ....................
DEF, 1 pt. + paraquat, /2pt.....
DEF, 1 pt. + paraquat, 1 pt......
DEF, 1 pt. + pyriclor, 2 pt.......
DEF, 1 pt. + pyriclor, 3 pt..
Seed cotton per
acre harvested
by picker'
Pounds
2,456 a
2,442 a
1,933 a
2,398 a
2,224 a
Cotton per acre
left in
unopened bolls'
Pounds
119a
204 a
349 b
90 a
125 a
'When values within columns are followed by the same letter there is no difference be-
cause of treatment, as figured by standard statistical methods; those followed by different
letters differ significantly.
TABLE 6. EFFECT OF PARAQUAT AND PYRICLOR IN COMBINATION WITH DEF ON LEAF
DROP AND.BOLL BURN OF COTTON, MARVYN RESEARCH UNIT. 1967
Boll burn Leaf drop,
Chemical and per acre rate October 6 October 10 October 10'
Per cent Per cent Per cent
DEF, 1/2 pt. --------------------------- G---.0a 0 a 76 a
DEF, 1 pt. + paraquat, 1/4 pt. 16 a 53 b 78 a
DEF, 1 pt. + paraquat, / pt. -65 b 92 b 55 b
DEF, 1 pt. + pyriclor, 2 pt. -- 0 a 3 a 85 a
DEF, 1 pt. + pyriclor, 3 pt. -0a 5 a' 80 a
When values within columns are followed by the same letter there is no difference be-
cause of treatment, as figured by standard statistical methods; those followed by different
letters differ significantly.
[4]
Harvesting
efficiency
Per cent
95.1
93.7
92.0
94.8
95.1
I ~ ,iriir
nr
TABLE 7. EFFECT OF PARAQUAT, PYRICLOR, AND ENDOTHALL IN COMBINATION WITH DEF
ON LEAF DROP OF COTTON, AGRONOMY FARM, AUBURN, 1967
Chemical and per acre rate 
Leaf drop' Regrowth,
Sept. 21 Sept. 27 Oct. 11 
Oct. 11
DEF, 1 pt. + paraquat, 1/2 pt...
DEF, 1 pt. + pyriclor, 2 pt.....
DEF, 1 pt. + endothall, 11/2 pt.
Untreated check-- - -
Per cent
75 a
70 a
65 a
0 b
Per cent
88 a
95 a
95 a
30 b
Per cent
95 a
95 a
95 a
40 b
Per cent
80 b
20c
85 b
90 a
1 When values within columns are followed by the same letter there is no difference be-
cause of treatment, as figured by standard statistical methods; those followed by different
letters differ significantly.
In the second experiment at the Mar-
vyn Research Unit treatments were ap-
plied when only 40 to 50 per cent of
bolls were open. Boll burn occurred on
53 and 92 per cent of unopened bolls
when 1/4 and 1/2 pint per acre paraquat
was applied with DEF. Leaf drop was
not delayed by 1/4 pint paraquat, but was
decreased slightly by the 1/2 pint per acre
rate, Table 6. No significant boll burn
was observed on plots treated with pyri-
clor. Leaf drop was the same as with
DEF alone.
RESULTS AT AGRONOMY FARM
The addition of either /2 pint para-
quat, 2 pints pyriclor, or 1/ pints endo-
thall to 1 pint DEF per acre gave com-
parable leaf drop. Practically all cotton
plants in all treatments except DEF +
pyriclor initiated regrowth, Table 7.
SUMMARY AND CONCLUSIONS
Addition of 1/ pint paraquat or more
to 1 pint per acre of DEF caused sub-
stantial burn to unoponed bolls. Obser-
vations of field scale application of para-
quat revealed that severity of burn was
decreased as level of maturity increased.
Immature bolls that received substantial
burn did not open sufficiently to be har-
vested with a mechanical picker. Pyriclor
caused slight boll burn even at the high-
est rate. Regrowth was inhibited by pyri-
clor at rate of 2 pints per acre or more.
Endothall and paraquat did not prevent
regrowth.
[5 ]