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Boll openers in cotton: effectiveness and environmental influences
Field Crops Research 67 (2000) 83±90
Boll openers in cotton: effectiveness and environmental in¯uences Alexander M. Stewart*, Keith L. Edmisten, Randy Wells Department of Crop Science, North Carolina State University, Box 7620, NCSU, Raleigh, NC 27695-7620, USA Received 6 September 1999; received in revised form 29 March 2000; accepted 29 March 2000
Abstract The indeterminate growth of cotton (Gossypium hirsutum L.) often results in a boll population at various stages of maturity when the crop is harvested. Boll opening compounds can be used to facilitate harvest by accelerating the opening of green bolls. Field trials were conducted at two locations in 1996 and 1997 to test the ef®cacy of four commercially available boll openers that stimulate ethylene production or desiccate the plant. Two of these boll openers are new to the marketplace: FinishTM, ethephoncyclanilide (2-chloroethyl phosphonic acid1-(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid), and CottonQuickTM, ethephonAMADS (2-chloroethyl phosphonic acid1-aminomethanamide dihydrogen tetraoxosulfate). Open bolls were hand harvested at 3±7 days intervals after application of the boll openers, and environmental conditions in conjunction with these harvests were recorded. The desiccant, paraquat (1,10 -dimethyl-4,40 -bipyridinium dichloride), was found to have erratic boll opening activity. Two products that contain ethephon plus the synergists cyclanilide or AMADS were found to have equal or higher rates of boll opening than ethephon alone. The rate of boll opening of all compounds was in¯uenced more by the accumulation of heat units than by the amount of time following the application of boll openers. Although erratic, boll opening activity from paraquat application can be signi®cant. Moreover, the reliability of ethephon based products, which are consistent boll openers, may be enhanced by formulations that contain a synergist. Heat unit accumulation may be used to predict and model the ef®cacy of boll opening with these harvest aides. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Boll openers; Cotton; Ethephon; Paraquat
1. Introduction Environmental conditions and cultural practices, particularly in the northern region of the upland cotton-producing areas of USA, can result in the
* Corresponding author. Tel.: 1-919-515-4061; fax: 1-919-515-7959. E-mail address: [email protected] (A.M. Stewart)
continued growth and delayed maturity of cotton. Cotton, being both perennial and indeterminate, continues to produce squares and ¯owers until an environmental factor such as temperature or limited assimilate supply causes a cessation of growth (Gipson and Joham, 1968; Smith et al., 1986). Consequently, the boll population at harvest is at various stages of maturity. To facilitate boll opening and the potential for once-over harvest of the crop, boll opening chemicals can be used to enhance the opening of green bolls on the plant (Cathey et al., 1982).
0378-4290/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 4 2 9 0 ( 0 0 ) 0 0 0 9 3 - 9
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The process of boll dehiscence is related to the vascular structure of the carpel, requires dehydration of the entire boll, and is in¯uenced by the plant growth hormone ethylene (Morgan, 1968; Morgan et al., 1971; Simpson and Marsh, 1977). Simpson and Marsh (1977) found that just prior to boll opening, the vascular elements form a corky layer at the base of the pedicel, impeding water movement into the boll. At the same time, inner layers of the vascular elements become tangentially arranged to the carpel, with subsequent dehydration causing the boll to dehisce instead of merely shrinking. Ethylene levels increase in bolls prior to dehiscence and signi®cant drying (Morgan et al., 1971; Abeles et al., 1992). Applications, therefore, of ethylene promoting or delivering compounds, as well as desiccating chemicals should hasten boll opening in cotton. Paraquat is a desiccant shown to have some use as a boll opener (Kirby and Stelzer, 1968), particularly as a follow-up treatment after defoliation (Cathey et al., 1982). Cathey (1979) found that when drying conditions were not good, dehiscence of bolls could be hastened after application of a desiccant such as paraquat. Ethephon, an ethylene precursor, is a widely used harvest aid and its effect on increasing the percentage of open bolls following application has been reported in a number of ®eld studies (Cathey et al., 1982; Garcia and Malm, 1985; Smith et al., 1986; Whitwell et al., 1987; Bariola, 1988). Boll development from anthesis to dehiscence is related to temperature and generally requires 910±950 growing degree days (DDs), based on 15.38C, which can require 40±80 days to accumulate depending on local environmental conditions (Cathey, 1986; Mauney, 1986). Due to decreased temperatures late in the growing season, bolls set after August 20 in NC typically do not mature in time for harvest (Edmisten, 1998). Lef¯er (1976) reported that bolls developed under favorable conditions did not open until 2 weeks after they had reached their maximum dry weight, therefore, some bolls set prior to August 20 may mature but not dehisce in time for harvest. The effects of harvest aids over time have been reported by several investigators (Cathey et al., 1982; Snipes and Cathey, 1992; Snipes and Baskin, 1994; Gwathmey and Hayes, 1997) but the in¯uence of accumulated heat units on harvest aid performance has rarely been studied. The in¯uence of temperature
on boll development is well known and models have been developed to provide an accumulated DD threshold for applying defoliants and terminating the crop (Cathey, 1985; Zhang et al., 1993). Gwathmey and Hayes (1997) presented evidence that likely temperature regimes following application should be considered when using ethephon as a boll opener in conjunction with a defoliant. A model that addresses the impact of environmental conditions on an individual harvest aid's performance may enhance the prediction of defoliant and boll opener effectiveness and aid in the selection of a boll opener. Recently, two enhanced ethephon products have been introduced for boll opening: ethephonAMADS and ethephoncyclanilide. Both products contain a synergist reported to increase the effectiveness of ethephon (Pedersen et al., 1997). Our objective was to determine the ef®cacy of these new products as harvest aids and to compare them to paraquat and ethephon treatments, as well as relate the various boll opener's activities to environmental in¯uences. 2. Materials and methods Cotton was planted at the following three NC locations: (1) Lewiston (Peanut Belt Research Station) in 1996 on a Goldsboro sandy loam (®ne loamy, siliceous, thermic Aquic Paleudult); (2) Rocky Mount (Upper Coastal Plain Research Station) in 1996 and 1997 on a Norfolk loamy sand (®ne loamy, siliceous, thermic Typic Kandiudult); and (3) at Clayton (Central Crops Research Station) on a Gilead sandy loam (clayey, kaolinite, thermic Aquic Hapludult). All locations were planted to cv. `Sure Grow 125' except Clayton which was planted to `Paymaster 1330RR'. Row spacing was 91 cm at Lewiston and Rocky Mount and 97 cm at Clayton. Plots were of four rows wide and 15.25 m long. Standard extension service guidelines for cotton production were followed in all tests. Experimental design was a randomized complete block with four replications. Treatments consisted of ethephon at 1.12 and 1.40 kg haÿ1, paraquat at 0.16, 0.29, 0.42, and 0.63 kg haÿ1, ethephonAMADS at 1.144.14 and 1.716.22 kg haÿ1, and ethephoncyclanilide at 1.120.56 and 1.680.84 kg haÿ1 at all locations. At Rocky Mount in 1996, tribufos (S,S,S-tributyl
A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
85
dividing the accumulated yield to date into the total yield for each 3 m section of row in each plot. Data were analyzed using SAS GLM procedures and mean separation was achieved using Fisher's protected LSD where applicable (SAS Institute, 1987). Wherever possible, data are presented combined over locations. Regressions for predicting responses of each treatment at each location over time and accumulated heat units were achieved using SAS NLIN procedures (SAS Institute, 1987). The predicted values for95%harvestableyieldwerethensubjectedtoanalysis of variance with the four locations as replications. In¯uences of solar radiation and relative humidity on boll opening were investigated, but no clear association was seen (data not shown). Daily maximum and minimum temperatures, and rainfall were collected by the experimental stations. Historical weather data were assessed at the Southeast Regional Climate Center's CIRRUS database. Cumulative DDs were calculated using the formula DD[maximum temperature (8C)ÿ15.38C]2/[2(maximum temperature (8C)ÿminimum temp (8C)] as described by Fry (1983).
phosphotrithioate) was applied alone and in a tankmix with all other treatments at 1.26 kg haÿ1. At all other locations, tribufos was applied alone and in a tankmix with other treatments at 0.42 kg haÿ1. Additionally, a treatment of ethephoncyclanilide alone at 1.680.84 kg haÿ1 was applied in 1997. An untreated check was maintained at all locations. To evaluate the maximum amount of boll opening possible, all treatments were applied when visual ratings revealed 25± 35% open bolls. Treatments were applied to all four rows of a plot with a CO2-pressurized backpack or high-clearance sprayer modi®ed for plot use delivering 150 haÿ1 through two hollow-cone nozzles per row at 207 kPa. Prior to treatment, a 3 m section of an inside row in each plot was marked. Starting from the day of application, seedcotton was hand-harvested from this section every 3±7 days until all bolls were open, or frost terminated the crop. A boll was considered harvestable if one or more locks were suf®ciently ¯uffed to be potentially removed by a spindle picker. Harvestable yield for each date was determined by
Table 1 Harvestable yield (%) of boll openers for 1, 2, and 3 weeks after treatment in 1996a Treatment
ai (kg haÿ1)
Harvestable yield (%) Rocky Mount
Lewiston
7 days
14 days
0.42
83.1 d 82.8 d
93.0 e 93.3 e
Ethephonb
1.12 1.40
83.6 d 91.5 abc
96.4 bcd 99.3 a
Paraquatb
0.16 0.29 0.42 0.63
84.5 84.5 85.8 86.2
96.1 94.0 97.3 97.0
EthephonAMADSb
1.14c 1.71d
88.0 bcd 94.3 a
99.3 99.1 ab
Ethephoncyclanilideb
1.12e 1.68f
91.7 ab 91.8 ab 5.4 4.3
98.4 abc 98.4 abc 2.7 1.9
Check Tribufos
LSD0.05 C.V. (%) a
d d d cd
cd de abc abc
21 days
7 days
14 days
21 days
34.9 53.0
45.8 c 66.2 ab
73.1 e 87.1 bcd
99.5 a 100.0 a
42.6 39.5
65.8 ab 66.2 ab
93.0 abcd 92.9 abcd
99.0 97.9 99.7 100.0
51.9 37.0 51.1 47.7
67.7 56.8 76.1 64.3
93.2 84.2 92.8 85.9
100.0 a 100.0 a
33.6 39.7
71.7 ab 79.7 a
94.4 abc 96.9 a
99.8 a 99.8 a 1.1 0.8
48.2 45.8 NS 29.5
75.8 a 80.9 a 17.2 17.6
95.6 ab 96.6 a 9.0 6.9
98.0 bc 98.2 bc
ab c a a
Figures followed by the same letter do not differ signi®cantly (P0.05). Tank mixed with 1.26 kg haÿ1 tribufos at Rocky Mount and 0.42 kg haÿ1 tribufos at Lewiston. c Indicates kg haÿ1 ethephon. Contains 4.14 kg haÿ1 AMADS. d Indicates kg haÿ1 ethephon. Contains 6.22 kg haÿ1 AMADS. e Indicates kg haÿ1 ethephon. Contains 0.56 kg haÿ1 cyclanilide. f Indicates kg haÿ1 ethephon. Contains 0.84 kg haÿ1 cyclanilide. b
ab bc a ab
abc d abcd cd
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A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
Table 2 Harvestable yield (%) of boll openers for 1, 2, and 3 weeks after treatment in 1997a Treatment
ai (kg haÿ1)
Harvestable yield (%) Rocky Mount (%)
Clayton (%)
7 days
14 days
21 days
7 days
14 days
21 days
0.42
79.1 83.3
93.5 d 94.5 d
98.5 97.5
64.3 60.7
90.2 bcd 87.9 d
90.6 bcd 88.6 d
Ethephonb
1.12 1.40
84.7 82.9
96.4 bcd 97.9 abc
96.5 99.6
59.4 62.4
94.6 ab 94.2 abc
94.6 abc 94.8 abc
Paraquatb
0.16 0.29 0.42 0.63
80.3 81.6 80.8 86.2
93.4 95.8 96.2 96.2
d cd bcd bcd
96.5 98.1 98.4 97.9
69.4 71.0 65.0 72.0
88.9 89.5 87.6 90.3
88.9 90.3 88.4 90.6
EthephonAMADSb
1.14c 1.71d
86.2 85.7
98.1 abc 99.3 ab
99.4 99.9
63.1 68.9
96.8 a 97.4 a
97.1 a 97.8 a
Ethephoncyclanilideb
1.12e 1.68f 1.68f
90.6 87.3 93.3 NS 7.1
99.1 ab 99.2 ab 99.7 a 3.1 2.2
99.9 99.8 100.0 NS 1.4
68.5 62.0 56.5 NS 14.0
96.0 a 96.0 a 87.6 a 5.5 4.2
96.1 ab 96.3 a 97.9 a 5.5 4.1
Check Tribufos
Ethephoncyclanilide LSD0.05 C.V. (%)
cd bcd d bcd
d cd d bcd
a
Figures followed by the same letter do not differ signi®cantly (P0.05). Tank mixed with 0.42 kg haÿ1 tribufos. c Indicates kg haÿ1 ethephon. Contains 4.14 kg haÿ1 AMADS. d Indicates kg haÿ1 ethephon. Contains 6.22 kg haÿ1 AMADS. e Indicates kg haÿ1 ethephon. Contains 0.56 kg haÿ1 cyclanilide. f Indicates kg haÿ1 ethephon. Contains 0.84 kg haÿ1 cyclanilide. b
3. Results and discussion Tables 1 and 2 show weekly percent harvestable yield of each treatment at each location. With the exception of the 1.40 kg haÿ1 rate of ethephon at Rocky Mount in 1997, ethephonAMADS and ethephoncyclanilide showed a numeric trend to consistently open bolls at a faster rate than ethephon alone or paraquat. Except for the 7 days measurement at Rocky Mount in 1996, no rate response was observed within the ethephon plus synergist treatments. Ethephon showed a rate response at 7 and 14 days at Rocky Mount in 1996 (Table 1), but no response at the other locations and dates of harvest. At least one rate of ethephon was statistically comparable to the ethephon plus synergist treatments for percent harvestable yield at all locations. Paraquat response in 1996 was inconsistent with the 0.29 kg haÿ1 treatment slower than all other boll openers (Table 1). At Rocky Mount in 1996 and 1997, paraquat at 0.16, 0.42, and 0.63 kg haÿ1 provided 95%
harvestable yield within 14 or 21 days (Tables 1 and 2). Cathey (1979) found boll opening performance of paraquat at 0.14 kg haÿ1 to be sensitive to evapotranspiration rates. Because paraquat is a desiccant, its overall boll opening activity may be more sensitive to rainfall and humidity compared to the hormone delivering ethephon products, possibly explaining its erratic response, although no relation to relative humidity could be established (data not shown). A signi®cant (P<0.05) location by treatment effect for percent harvestable yield is partially explained by environmental differences over locations (Fig. 1). In 1996, accumulation of DDs was slower at Lewiston than Rocky Mount, and the Lewiston location had more signi®cant rainfall in the ®rst 12 days after treatment. The number of days prior to 95% harvestable yield, averaged for all boll openers, was much greater at Lewiston than Rocky Mount in 1996 (Fig. 2). The two 1996 locations were very similar, however, in the heat units required to reach the 95% level, suggesting that the effect of DD accumulation on boll opening
A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
Fig. 1. Rainfall and DD (15.38C base) accumulation at Rocky Mount in 1996 and 1997, Lewiston in 1996, and Clayton in 1997.
Fig. 2. Harvestable yield (%) for test average at four environments in response to DD (15.38C base) accumulation and time.
87
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A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
is greater than the effect of amount of time after treatment. Cooler, wetter conditions soon after treatment at Lewiston help explain the delayed response time to 95% harvestable yield at that location. Despite the similar accumulation of DDs at Rocky Mount and Clayton in 1997, boll opening was delayed at Clayton (Figs. 1 and 2). Because `Sure Grow 125' and `Paymaster 1330RR' are similar cultivars in terms of maturity, it is unlikely that cultivar differences account for the slower response at Clayton. A number of small rainfall events occurred 15±21 days after treatment at Clayton (Fig. 1), and little boll opening occurred during this time span (Fig. 2). The Clayton location also required more accumulated DDs to reach 95% harvestable yield (Fig. 2). Cathey (1986) stated that defoliation is reduced under conditions of low temperatures and suggested 168C as a minimum; extended overcast also reduces defoliation (Brown and Hyer, 1954). Delayed boll opening at Clayton was possibly due to the combination of higher humidity, lower temperature, and lower light intensity over the 15 to 21-day period. With the exception of Clayton in 1997, the amount of accumulated DDs required to reach 95% harvestable yield was very similar for three of the four locations, although Lewiston required fewer DDs (Fig. 2). All test sites, except Clayton in 1997, required about 120 heat units from treatment to reach 95% harvestable yield, suggesting that the accumulation of heat units is the main factor in determining how quickly boll openers act (Fig. 2). Data from Clayton in 1997 and Lewiston in 1996 suggest that a combination of DDs and time in¯uence boll opening (Fig. 2). Further evidence of the in¯uence of accumulated heat units and amount of time after application on the activity of these boll openers is shown in Table 3. The number of DDs required to attain 95% harvestable yield was smallest for ethephonAMADS and ethephoncyclanilide compared to all other treatments except for ethephon at the 1.40 kg haÿ1 rate. This is consistent with weekly results from Tables 1 and 2, and is shown also in the number of days required for 95% harvestable yield in Table 3. Although the results shown in Table 3 show a consistent response to accumulated heat units and time among all boll openers, the data reported in Fig. 2 indicate that accumulated heat units may be a more consistent predictor of the rate of boll opening than time. Although the effect
Table 3 Number of DDs (15.38C base) and actual days predicted to reach 95% harvestable yield averaged across four environments in 2 yearsa Compound
ai (kg haÿ1)
DDs
Days
Check Tribufos
0.42
146.1 c 149.1 c
21.0 e 20.0 de
Ethephonb
1.12 1.40
132.5 bc 119.7 ab
17.3 bcd 16.0 abc
Paraquatb
0.16 0.29 0.42 0.63
143.3 133.7 136.1 134.0
18.3 18.1 17.6 17.9
EthephonAMADSb
1.14c 1.71d
117.7 ab 104.4 a
15.5 abc 13.8 a
Ethephoncyclanilideb
1.12e 1.68f
108.8 a 109.7 a 20.2 11.0
14.5 ab 14.3 a 2.9 12.0
LSD0.05 C.V. (%)
c bc bc bc
cde cde cd cd
a
Figures followed by the same letter do not differ signi®cantly (P0.05). b Tank mixed with 1.26 kg haÿ1 tribufos at Rocky Mount, 1996. All other locations tank mixed with 0.42 kg haÿ1 tribufos. c Indicates kg haÿ1 ethephon. Contains 4.14 kg haÿ1 AMADS. d Indicates kg haÿ1 ethephon. Contains 6.22 kg haÿ1 AMADS. e Indicates kg haÿ1 ethephon. Contains 0.56 kg haÿ1 cyclanilide. f Indicates kg haÿ1 ethephon. Contains 0.84 kg haÿ1 cyclanilide.
of the individual boll openers has not been previously reported, this response in general would be expected given the established relationship between temperature and cotton growth and development (McMahon and Low, 1972; Mauney, 1986). 4. Conclusions Differences do exist between the ef®cacy of the boll openers tested in this study. Although paraquat possessed boll opening activity, results were inconsistent and inferior to those observed with ethephon under all but cooler conditions. Rate response to paraquat was inconsistent as well, suggesting that further research is needed to fully understand the interaction between environmental conditions and the rate response of paraquat. Because of paraquat's limitations as a defoliant, its use as a boll opener may be better suited to
A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
follow-up treatments after the crop has been defoliated. Paraquat is relatively inexpensive compared to the ethephon products; therefore additional research into its use is warranted. The bene®t of a synergist with ethephon was con®rmed by these studies. Under a wide variety of conditions, the ethephon plus synergist compounds were equal to or better than ethephon alone in boll opening activity. EthephonAMADS and ethephoncyclanilide were similar in terms of the rate of boll opening over time at all locations, and there was little rate response within these treatments. Future work should examine reduced rates of application consistent with high boll opening activity. The activity of all boll openers tested was greatly in¯uenced by the accumulation of heat units after application, an area in which little information is available. Future investigations should attempt to model boll opening response to heat units at additional stages of percent open bolls. The time needed to accumulate the required number of heat units for each compound to provide adequate boll opening would be expected to increase with the onset of progressively cooler fall temperatures. Additional research should investigate the feasibility of setting speci®c dates after which the application of a given boll opening compound would not be practical. Acknowledgements The authors wish to thank Edward Straughn for his technical assistance in conducting this study. References Abeles, F.B., Morgan, P.W., Saltveit, M.E., 1992. Ethylene in Plant Biology, 2nd Edition. Academic Press, New York. Bariola, L.A., 1988. Response of cotton varieties grown in a short season to ethephon and thidiazuron in the arid southwest. In: Brown, J.M., Richter, D.A. (Eds.), Proceedings of the Beltwide Cotton Production Research Conference, New Orleans, LA, January 3±8, 1988. National Cotton Council of America, Memphis, TN, pp. 302±303. Brown, L.C., Hyer, A.H., 1954. A preliminary report on the in¯uence varying periods of darkness on the defoliability of several varieties of cotton. In: Proceedings of the Beltwide Cotton Defoliation Conference, Vol. 8, p. 44. Cathey, G.W., 1979. Acceleration of boll dehiscence with desiccant chemicals. Agron. J. 71, 505±508.
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Cathey, G.W., 1985. Heat units and cotton development in the midsouth. In: Brown, J.M., Nelson, T.C. (Eds.), Proceedings of the Beltwide Cotton Production Research Conference, New Orleans, LA, January 6±11, 1985. National Cotton Council of America, Memphis, TN, p. 368. Cathey, G.W., 1986. Physiology of defoliation in cotton production. In: Mauney, J.R., Stewart, J.M. (Eds.), Cotton Physiology. The Cotton Foundation, Memphis, TN. Cathey, G.W., Luckett, K.E., Rayburn, S.T., 1982. Accelerated boll dehiscence with growth regulator and desiccant chemicals. Field Crop Res. 5, 113±120. Edmisten, K.L., 1998. The cotton plant. In: 1998 Cotton Information. North Carolina Cooperative Extension Service, Pub. AG-417. Fry, K.E., 1983. Heat unit calculations in cotton crop and insect models. USDA, ARS, Adv. Agric. Tech. AAT-W-23. Garcia, O., Malm, N.R., 1985. Effect of ethephon and Pix growth regulators on yield and maturity of upland cotton. In: Brown, J.M., Nelson, T.C. (Eds.), Proceedings of the Beltwide Cotton Production Research Conference, New Orleans, LA, January 6±11, 1985. National Cotton Council of America, Memphis, TN, pp. 38±40. Gipson, J.R., Joham, H.E., 1968. In¯uence of night temperature on growth and development of cotton (Gossypium hirsutum L.). II. Fruiting and boll development. Agron. J. 60, 292± 295. Gwathmey, C.O., Hayes, R.M., 1997. Harvest aid interactions under different temperature regimes in ®eld grown cotton. J. Cotton Sci. 1, 1±10. Kirby, B.W., Stelzer, L.R., 1968. Paraquat as a cotton harvest aid chemical: Effect on lint and seed quality. In: Proceedings of Beltwide Cotton Production Research Conference. Hot Springs, AR, January 9±10, 1968. National Cotton Council of America, Memphis, TN, pp. 68±72. Lef¯er, H.R., 1976. Development of cotton fruit. I. Accumulation and distribution of dry matter. Agron. J. 68, 855±857. Mauney, J.R., 1986. Vegetative growth and development of fruiting sites. In: Mauney, J.R., Stewart, J.M. (Eds.), Cotton Physiology. The Cotton Foundation, Memphis, TN. McMahon, J., Low, A., 1972. Growing degree days as a measure of temperature effects on cotton. Cotton Growth Rev. 49, 39±49. Morgan, P.W., 1968. Effect of Amchem 66±329 on defoliation and ethylene production by cotton. In: Proceedings of the Beltwide Cotton Production Research Conference, Hot Springs, AR, January 9±10, 1968. National Cotton Council of America, Memphis, TN, pp. 72±78. Morgan, P.W., Beyer, E.M., Lipe, J.A., McAfee, J.A., 1971. Ethylene, a regulator in cotton leaf shed and boll opening. In: Proceedings of the Beltwide Cotton Production Research Conference, Atlanta, GA, January 12±13, 1971. National Cotton Council of America, Memphis, TN, pp. 42±43. Pedersen, M.K., Burton, J.D., Coble, H.D., 1997. Ef®cacy of Finish and its mode of action. In: Dugger, P., Richter, D.A. (Eds.), Proceedings of the Beltwide Cotton Conference, New Orleans, LA, January 7±10, 1997. National Cotton Council of America, Memphis, TN, pp. 1363±1365.
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SAS Institute Inc., 1987. SAS Language Guide for Personal Computers, Version 6.03. Sas Institute, Cary, NC. Simpson, M.E., Marsh, P.B., 1977. Vascular anatomy of cotton carpels as revealed by digestion in ruminal ¯uid. Crop Sci. 17, 819±821. Smith, C.W., Cothren, J.T., Varvil, J.J., 1986. Yield and ®ber quality of cotton following application of 2-chloroethyl phosphonic acid. Agron. J. 78, 814±818. Snipes, C.E., Baskin, C.C., 1994. In¯uence of early defoliation on cotton yield seed quality and ®ber properties. Field Crops Res. 37, 137±143.
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Boll openers in cotton: effectiveness and environmental in¯uences Alexander M. Stewart*, Keith L. Edmisten, Randy Wells Department of Crop Science, North Carolina State University, Box 7620, NCSU, Raleigh, NC 27695-7620, USA Received 6 September 1999; received in revised form 29 March 2000; accepted 29 March 2000
Abstract The indeterminate growth of cotton (Gossypium hirsutum L.) often results in a boll population at various stages of maturity when the crop is harvested. Boll opening compounds can be used to facilitate harvest by accelerating the opening of green bolls. Field trials were conducted at two locations in 1996 and 1997 to test the ef®cacy of four commercially available boll openers that stimulate ethylene production or desiccate the plant. Two of these boll openers are new to the marketplace: FinishTM, ethephoncyclanilide (2-chloroethyl phosphonic acid1-(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid), and CottonQuickTM, ethephonAMADS (2-chloroethyl phosphonic acid1-aminomethanamide dihydrogen tetraoxosulfate). Open bolls were hand harvested at 3±7 days intervals after application of the boll openers, and environmental conditions in conjunction with these harvests were recorded. The desiccant, paraquat (1,10 -dimethyl-4,40 -bipyridinium dichloride), was found to have erratic boll opening activity. Two products that contain ethephon plus the synergists cyclanilide or AMADS were found to have equal or higher rates of boll opening than ethephon alone. The rate of boll opening of all compounds was in¯uenced more by the accumulation of heat units than by the amount of time following the application of boll openers. Although erratic, boll opening activity from paraquat application can be signi®cant. Moreover, the reliability of ethephon based products, which are consistent boll openers, may be enhanced by formulations that contain a synergist. Heat unit accumulation may be used to predict and model the ef®cacy of boll opening with these harvest aides. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Boll openers; Cotton; Ethephon; Paraquat
1. Introduction Environmental conditions and cultural practices, particularly in the northern region of the upland cotton-producing areas of USA, can result in the
* Corresponding author. Tel.: 1-919-515-4061; fax: 1-919-515-7959. E-mail address: [email protected] (A.M. Stewart)
continued growth and delayed maturity of cotton. Cotton, being both perennial and indeterminate, continues to produce squares and ¯owers until an environmental factor such as temperature or limited assimilate supply causes a cessation of growth (Gipson and Joham, 1968; Smith et al., 1986). Consequently, the boll population at harvest is at various stages of maturity. To facilitate boll opening and the potential for once-over harvest of the crop, boll opening chemicals can be used to enhance the opening of green bolls on the plant (Cathey et al., 1982).
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The process of boll dehiscence is related to the vascular structure of the carpel, requires dehydration of the entire boll, and is in¯uenced by the plant growth hormone ethylene (Morgan, 1968; Morgan et al., 1971; Simpson and Marsh, 1977). Simpson and Marsh (1977) found that just prior to boll opening, the vascular elements form a corky layer at the base of the pedicel, impeding water movement into the boll. At the same time, inner layers of the vascular elements become tangentially arranged to the carpel, with subsequent dehydration causing the boll to dehisce instead of merely shrinking. Ethylene levels increase in bolls prior to dehiscence and signi®cant drying (Morgan et al., 1971; Abeles et al., 1992). Applications, therefore, of ethylene promoting or delivering compounds, as well as desiccating chemicals should hasten boll opening in cotton. Paraquat is a desiccant shown to have some use as a boll opener (Kirby and Stelzer, 1968), particularly as a follow-up treatment after defoliation (Cathey et al., 1982). Cathey (1979) found that when drying conditions were not good, dehiscence of bolls could be hastened after application of a desiccant such as paraquat. Ethephon, an ethylene precursor, is a widely used harvest aid and its effect on increasing the percentage of open bolls following application has been reported in a number of ®eld studies (Cathey et al., 1982; Garcia and Malm, 1985; Smith et al., 1986; Whitwell et al., 1987; Bariola, 1988). Boll development from anthesis to dehiscence is related to temperature and generally requires 910±950 growing degree days (DDs), based on 15.38C, which can require 40±80 days to accumulate depending on local environmental conditions (Cathey, 1986; Mauney, 1986). Due to decreased temperatures late in the growing season, bolls set after August 20 in NC typically do not mature in time for harvest (Edmisten, 1998). Lef¯er (1976) reported that bolls developed under favorable conditions did not open until 2 weeks after they had reached their maximum dry weight, therefore, some bolls set prior to August 20 may mature but not dehisce in time for harvest. The effects of harvest aids over time have been reported by several investigators (Cathey et al., 1982; Snipes and Cathey, 1992; Snipes and Baskin, 1994; Gwathmey and Hayes, 1997) but the in¯uence of accumulated heat units on harvest aid performance has rarely been studied. The in¯uence of temperature
on boll development is well known and models have been developed to provide an accumulated DD threshold for applying defoliants and terminating the crop (Cathey, 1985; Zhang et al., 1993). Gwathmey and Hayes (1997) presented evidence that likely temperature regimes following application should be considered when using ethephon as a boll opener in conjunction with a defoliant. A model that addresses the impact of environmental conditions on an individual harvest aid's performance may enhance the prediction of defoliant and boll opener effectiveness and aid in the selection of a boll opener. Recently, two enhanced ethephon products have been introduced for boll opening: ethephonAMADS and ethephoncyclanilide. Both products contain a synergist reported to increase the effectiveness of ethephon (Pedersen et al., 1997). Our objective was to determine the ef®cacy of these new products as harvest aids and to compare them to paraquat and ethephon treatments, as well as relate the various boll opener's activities to environmental in¯uences. 2. Materials and methods Cotton was planted at the following three NC locations: (1) Lewiston (Peanut Belt Research Station) in 1996 on a Goldsboro sandy loam (®ne loamy, siliceous, thermic Aquic Paleudult); (2) Rocky Mount (Upper Coastal Plain Research Station) in 1996 and 1997 on a Norfolk loamy sand (®ne loamy, siliceous, thermic Typic Kandiudult); and (3) at Clayton (Central Crops Research Station) on a Gilead sandy loam (clayey, kaolinite, thermic Aquic Hapludult). All locations were planted to cv. `Sure Grow 125' except Clayton which was planted to `Paymaster 1330RR'. Row spacing was 91 cm at Lewiston and Rocky Mount and 97 cm at Clayton. Plots were of four rows wide and 15.25 m long. Standard extension service guidelines for cotton production were followed in all tests. Experimental design was a randomized complete block with four replications. Treatments consisted of ethephon at 1.12 and 1.40 kg haÿ1, paraquat at 0.16, 0.29, 0.42, and 0.63 kg haÿ1, ethephonAMADS at 1.144.14 and 1.716.22 kg haÿ1, and ethephoncyclanilide at 1.120.56 and 1.680.84 kg haÿ1 at all locations. At Rocky Mount in 1996, tribufos (S,S,S-tributyl
A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
85
dividing the accumulated yield to date into the total yield for each 3 m section of row in each plot. Data were analyzed using SAS GLM procedures and mean separation was achieved using Fisher's protected LSD where applicable (SAS Institute, 1987). Wherever possible, data are presented combined over locations. Regressions for predicting responses of each treatment at each location over time and accumulated heat units were achieved using SAS NLIN procedures (SAS Institute, 1987). The predicted values for95%harvestableyieldwerethensubjectedtoanalysis of variance with the four locations as replications. In¯uences of solar radiation and relative humidity on boll opening were investigated, but no clear association was seen (data not shown). Daily maximum and minimum temperatures, and rainfall were collected by the experimental stations. Historical weather data were assessed at the Southeast Regional Climate Center's CIRRUS database. Cumulative DDs were calculated using the formula DD[maximum temperature (8C)ÿ15.38C]2/[2(maximum temperature (8C)ÿminimum temp (8C)] as described by Fry (1983).
phosphotrithioate) was applied alone and in a tankmix with all other treatments at 1.26 kg haÿ1. At all other locations, tribufos was applied alone and in a tankmix with other treatments at 0.42 kg haÿ1. Additionally, a treatment of ethephoncyclanilide alone at 1.680.84 kg haÿ1 was applied in 1997. An untreated check was maintained at all locations. To evaluate the maximum amount of boll opening possible, all treatments were applied when visual ratings revealed 25± 35% open bolls. Treatments were applied to all four rows of a plot with a CO2-pressurized backpack or high-clearance sprayer modi®ed for plot use delivering 150 haÿ1 through two hollow-cone nozzles per row at 207 kPa. Prior to treatment, a 3 m section of an inside row in each plot was marked. Starting from the day of application, seedcotton was hand-harvested from this section every 3±7 days until all bolls were open, or frost terminated the crop. A boll was considered harvestable if one or more locks were suf®ciently ¯uffed to be potentially removed by a spindle picker. Harvestable yield for each date was determined by
Table 1 Harvestable yield (%) of boll openers for 1, 2, and 3 weeks after treatment in 1996a Treatment
ai (kg haÿ1)
Harvestable yield (%) Rocky Mount
Lewiston
7 days
14 days
0.42
83.1 d 82.8 d
93.0 e 93.3 e
Ethephonb
1.12 1.40
83.6 d 91.5 abc
96.4 bcd 99.3 a
Paraquatb
0.16 0.29 0.42 0.63
84.5 84.5 85.8 86.2
96.1 94.0 97.3 97.0
EthephonAMADSb
1.14c 1.71d
88.0 bcd 94.3 a
99.3 99.1 ab
Ethephoncyclanilideb
1.12e 1.68f
91.7 ab 91.8 ab 5.4 4.3
98.4 abc 98.4 abc 2.7 1.9
Check Tribufos
LSD0.05 C.V. (%) a
d d d cd
cd de abc abc
21 days
7 days
14 days
21 days
34.9 53.0
45.8 c 66.2 ab
73.1 e 87.1 bcd
99.5 a 100.0 a
42.6 39.5
65.8 ab 66.2 ab
93.0 abcd 92.9 abcd
99.0 97.9 99.7 100.0
51.9 37.0 51.1 47.7
67.7 56.8 76.1 64.3
93.2 84.2 92.8 85.9
100.0 a 100.0 a
33.6 39.7
71.7 ab 79.7 a
94.4 abc 96.9 a
99.8 a 99.8 a 1.1 0.8
48.2 45.8 NS 29.5
75.8 a 80.9 a 17.2 17.6
95.6 ab 96.6 a 9.0 6.9
98.0 bc 98.2 bc
ab c a a
Figures followed by the same letter do not differ signi®cantly (P0.05). Tank mixed with 1.26 kg haÿ1 tribufos at Rocky Mount and 0.42 kg haÿ1 tribufos at Lewiston. c Indicates kg haÿ1 ethephon. Contains 4.14 kg haÿ1 AMADS. d Indicates kg haÿ1 ethephon. Contains 6.22 kg haÿ1 AMADS. e Indicates kg haÿ1 ethephon. Contains 0.56 kg haÿ1 cyclanilide. f Indicates kg haÿ1 ethephon. Contains 0.84 kg haÿ1 cyclanilide. b
ab bc a ab
abc d abcd cd
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Table 2 Harvestable yield (%) of boll openers for 1, 2, and 3 weeks after treatment in 1997a Treatment
ai (kg haÿ1)
Harvestable yield (%) Rocky Mount (%)
Clayton (%)
7 days
14 days
21 days
7 days
14 days
21 days
0.42
79.1 83.3
93.5 d 94.5 d
98.5 97.5
64.3 60.7
90.2 bcd 87.9 d
90.6 bcd 88.6 d
Ethephonb
1.12 1.40
84.7 82.9
96.4 bcd 97.9 abc
96.5 99.6
59.4 62.4
94.6 ab 94.2 abc
94.6 abc 94.8 abc
Paraquatb
0.16 0.29 0.42 0.63
80.3 81.6 80.8 86.2
93.4 95.8 96.2 96.2
d cd bcd bcd
96.5 98.1 98.4 97.9
69.4 71.0 65.0 72.0
88.9 89.5 87.6 90.3
88.9 90.3 88.4 90.6
EthephonAMADSb
1.14c 1.71d
86.2 85.7
98.1 abc 99.3 ab
99.4 99.9
63.1 68.9
96.8 a 97.4 a
97.1 a 97.8 a
Ethephoncyclanilideb
1.12e 1.68f 1.68f
90.6 87.3 93.3 NS 7.1
99.1 ab 99.2 ab 99.7 a 3.1 2.2
99.9 99.8 100.0 NS 1.4
68.5 62.0 56.5 NS 14.0
96.0 a 96.0 a 87.6 a 5.5 4.2
96.1 ab 96.3 a 97.9 a 5.5 4.1
Check Tribufos
Ethephoncyclanilide LSD0.05 C.V. (%)
cd bcd d bcd
d cd d bcd
a
Figures followed by the same letter do not differ signi®cantly (P0.05). Tank mixed with 0.42 kg haÿ1 tribufos. c Indicates kg haÿ1 ethephon. Contains 4.14 kg haÿ1 AMADS. d Indicates kg haÿ1 ethephon. Contains 6.22 kg haÿ1 AMADS. e Indicates kg haÿ1 ethephon. Contains 0.56 kg haÿ1 cyclanilide. f Indicates kg haÿ1 ethephon. Contains 0.84 kg haÿ1 cyclanilide. b
3. Results and discussion Tables 1 and 2 show weekly percent harvestable yield of each treatment at each location. With the exception of the 1.40 kg haÿ1 rate of ethephon at Rocky Mount in 1997, ethephonAMADS and ethephoncyclanilide showed a numeric trend to consistently open bolls at a faster rate than ethephon alone or paraquat. Except for the 7 days measurement at Rocky Mount in 1996, no rate response was observed within the ethephon plus synergist treatments. Ethephon showed a rate response at 7 and 14 days at Rocky Mount in 1996 (Table 1), but no response at the other locations and dates of harvest. At least one rate of ethephon was statistically comparable to the ethephon plus synergist treatments for percent harvestable yield at all locations. Paraquat response in 1996 was inconsistent with the 0.29 kg haÿ1 treatment slower than all other boll openers (Table 1). At Rocky Mount in 1996 and 1997, paraquat at 0.16, 0.42, and 0.63 kg haÿ1 provided 95%
harvestable yield within 14 or 21 days (Tables 1 and 2). Cathey (1979) found boll opening performance of paraquat at 0.14 kg haÿ1 to be sensitive to evapotranspiration rates. Because paraquat is a desiccant, its overall boll opening activity may be more sensitive to rainfall and humidity compared to the hormone delivering ethephon products, possibly explaining its erratic response, although no relation to relative humidity could be established (data not shown). A signi®cant (P<0.05) location by treatment effect for percent harvestable yield is partially explained by environmental differences over locations (Fig. 1). In 1996, accumulation of DDs was slower at Lewiston than Rocky Mount, and the Lewiston location had more signi®cant rainfall in the ®rst 12 days after treatment. The number of days prior to 95% harvestable yield, averaged for all boll openers, was much greater at Lewiston than Rocky Mount in 1996 (Fig. 2). The two 1996 locations were very similar, however, in the heat units required to reach the 95% level, suggesting that the effect of DD accumulation on boll opening
A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
Fig. 1. Rainfall and DD (15.38C base) accumulation at Rocky Mount in 1996 and 1997, Lewiston in 1996, and Clayton in 1997.
Fig. 2. Harvestable yield (%) for test average at four environments in response to DD (15.38C base) accumulation and time.
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is greater than the effect of amount of time after treatment. Cooler, wetter conditions soon after treatment at Lewiston help explain the delayed response time to 95% harvestable yield at that location. Despite the similar accumulation of DDs at Rocky Mount and Clayton in 1997, boll opening was delayed at Clayton (Figs. 1 and 2). Because `Sure Grow 125' and `Paymaster 1330RR' are similar cultivars in terms of maturity, it is unlikely that cultivar differences account for the slower response at Clayton. A number of small rainfall events occurred 15±21 days after treatment at Clayton (Fig. 1), and little boll opening occurred during this time span (Fig. 2). The Clayton location also required more accumulated DDs to reach 95% harvestable yield (Fig. 2). Cathey (1986) stated that defoliation is reduced under conditions of low temperatures and suggested 168C as a minimum; extended overcast also reduces defoliation (Brown and Hyer, 1954). Delayed boll opening at Clayton was possibly due to the combination of higher humidity, lower temperature, and lower light intensity over the 15 to 21-day period. With the exception of Clayton in 1997, the amount of accumulated DDs required to reach 95% harvestable yield was very similar for three of the four locations, although Lewiston required fewer DDs (Fig. 2). All test sites, except Clayton in 1997, required about 120 heat units from treatment to reach 95% harvestable yield, suggesting that the accumulation of heat units is the main factor in determining how quickly boll openers act (Fig. 2). Data from Clayton in 1997 and Lewiston in 1996 suggest that a combination of DDs and time in¯uence boll opening (Fig. 2). Further evidence of the in¯uence of accumulated heat units and amount of time after application on the activity of these boll openers is shown in Table 3. The number of DDs required to attain 95% harvestable yield was smallest for ethephonAMADS and ethephoncyclanilide compared to all other treatments except for ethephon at the 1.40 kg haÿ1 rate. This is consistent with weekly results from Tables 1 and 2, and is shown also in the number of days required for 95% harvestable yield in Table 3. Although the results shown in Table 3 show a consistent response to accumulated heat units and time among all boll openers, the data reported in Fig. 2 indicate that accumulated heat units may be a more consistent predictor of the rate of boll opening than time. Although the effect
Table 3 Number of DDs (15.38C base) and actual days predicted to reach 95% harvestable yield averaged across four environments in 2 yearsa Compound
ai (kg haÿ1)
DDs
Days
Check Tribufos
0.42
146.1 c 149.1 c
21.0 e 20.0 de
Ethephonb
1.12 1.40
132.5 bc 119.7 ab
17.3 bcd 16.0 abc
Paraquatb
0.16 0.29 0.42 0.63
143.3 133.7 136.1 134.0
18.3 18.1 17.6 17.9
EthephonAMADSb
1.14c 1.71d
117.7 ab 104.4 a
15.5 abc 13.8 a
Ethephoncyclanilideb
1.12e 1.68f
108.8 a 109.7 a 20.2 11.0
14.5 ab 14.3 a 2.9 12.0
LSD0.05 C.V. (%)
c bc bc bc
cde cde cd cd
a
Figures followed by the same letter do not differ signi®cantly (P0.05). b Tank mixed with 1.26 kg haÿ1 tribufos at Rocky Mount, 1996. All other locations tank mixed with 0.42 kg haÿ1 tribufos. c Indicates kg haÿ1 ethephon. Contains 4.14 kg haÿ1 AMADS. d Indicates kg haÿ1 ethephon. Contains 6.22 kg haÿ1 AMADS. e Indicates kg haÿ1 ethephon. Contains 0.56 kg haÿ1 cyclanilide. f Indicates kg haÿ1 ethephon. Contains 0.84 kg haÿ1 cyclanilide.
of the individual boll openers has not been previously reported, this response in general would be expected given the established relationship between temperature and cotton growth and development (McMahon and Low, 1972; Mauney, 1986). 4. Conclusions Differences do exist between the ef®cacy of the boll openers tested in this study. Although paraquat possessed boll opening activity, results were inconsistent and inferior to those observed with ethephon under all but cooler conditions. Rate response to paraquat was inconsistent as well, suggesting that further research is needed to fully understand the interaction between environmental conditions and the rate response of paraquat. Because of paraquat's limitations as a defoliant, its use as a boll opener may be better suited to
A.M. Stewart et al. / Field Crops Research 67 (2000) 83±90
follow-up treatments after the crop has been defoliated. Paraquat is relatively inexpensive compared to the ethephon products; therefore additional research into its use is warranted. The bene®t of a synergist with ethephon was con®rmed by these studies. Under a wide variety of conditions, the ethephon plus synergist compounds were equal to or better than ethephon alone in boll opening activity. EthephonAMADS and ethephoncyclanilide were similar in terms of the rate of boll opening over time at all locations, and there was little rate response within these treatments. Future work should examine reduced rates of application consistent with high boll opening activity. The activity of all boll openers tested was greatly in¯uenced by the accumulation of heat units after application, an area in which little information is available. Future investigations should attempt to model boll opening response to heat units at additional stages of percent open bolls. The time needed to accumulate the required number of heat units for each compound to provide adequate boll opening would be expected to increase with the onset of progressively cooler fall temperatures. Additional research should investigate the feasibility of setting speci®c dates after which the application of a given boll opening compound would not be practical. Acknowledgements The authors wish to thank Edward Straughn for his technical assistance in conducting this study. References Abeles, F.B., Morgan, P.W., Saltveit, M.E., 1992. Ethylene in Plant Biology, 2nd Edition. Academic Press, New York. Bariola, L.A., 1988. Response of cotton varieties grown in a short season to ethephon and thidiazuron in the arid southwest. In: Brown, J.M., Richter, D.A. (Eds.), Proceedings of the Beltwide Cotton Production Research Conference, New Orleans, LA, January 3±8, 1988. National Cotton Council of America, Memphis, TN, pp. 302±303. Brown, L.C., Hyer, A.H., 1954. A preliminary report on the in¯uence varying periods of darkness on the defoliability of several varieties of cotton. In: Proceedings of the Beltwide Cotton Defoliation Conference, Vol. 8, p. 44. Cathey, G.W., 1979. Acceleration of boll dehiscence with desiccant chemicals. Agron. J. 71, 505±508.
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Cathey, G.W., 1985. Heat units and cotton development in the midsouth. In: Brown, J.M., Nelson, T.C. (Eds.), Proceedings of the Beltwide Cotton Production Research Conference, New Orleans, LA, January 6±11, 1985. National Cotton Council of America, Memphis, TN, p. 368. Cathey, G.W., 1986. Physiology of defoliation in cotton production. In: Mauney, J.R., Stewart, J.M. (Eds.), Cotton Physiology. The Cotton Foundation, Memphis, TN. Cathey, G.W., Luckett, K.E., Rayburn, S.T., 1982. Accelerated boll dehiscence with growth regulator and desiccant chemicals. Field Crop Res. 5, 113±120. Edmisten, K.L., 1998. The cotton plant. In: 1998 Cotton Information. North Carolina Cooperative Extension Service, Pub. AG-417. Fry, K.E., 1983. Heat unit calculations in cotton crop and insect models. USDA, ARS, Adv. Agric. Tech. AAT-W-23. Garcia, O., Malm, N.R., 1985. Effect of ethephon and Pix growth regulators on yield and maturity of upland cotton. In: Brown, J.M., Nelson, T.C. (Eds.), Proceedings of the Beltwide Cotton Production Research Conference, New Orleans, LA, January 6±11, 1985. National Cotton Council of America, Memphis, TN, pp. 38±40. Gipson, J.R., Joham, H.E., 1968. In¯uence of night temperature on growth and development of cotton (Gossypium hirsutum L.). II. Fruiting and boll development. Agron. J. 60, 292± 295. Gwathmey, C.O., Hayes, R.M., 1997. Harvest aid interactions under different temperature regimes in ®eld grown cotton. J. Cotton Sci. 1, 1±10. Kirby, B.W., Stelzer, L.R., 1968. Paraquat as a cotton harvest aid chemical: Effect on lint and seed quality. In: Proceedings of Beltwide Cotton Production Research Conference. Hot Springs, AR, January 9±10, 1968. National Cotton Council of America, Memphis, TN, pp. 68±72. Lef¯er, H.R., 1976. Development of cotton fruit. I. Accumulation and distribution of dry matter. Agron. J. 68, 855±857. Mauney, J.R., 1986. Vegetative growth and development of fruiting sites. In: Mauney, J.R., Stewart, J.M. (Eds.), Cotton Physiology. The Cotton Foundation, Memphis, TN. McMahon, J., Low, A., 1972. Growing degree days as a measure of temperature effects on cotton. Cotton Growth Rev. 49, 39±49. Morgan, P.W., 1968. Effect of Amchem 66±329 on defoliation and ethylene production by cotton. In: Proceedings of the Beltwide Cotton Production Research Conference, Hot Springs, AR, January 9±10, 1968. National Cotton Council of America, Memphis, TN, pp. 72±78. Morgan, P.W., Beyer, E.M., Lipe, J.A., McAfee, J.A., 1971. Ethylene, a regulator in cotton leaf shed and boll opening. In: Proceedings of the Beltwide Cotton Production Research Conference, Atlanta, GA, January 12±13, 1971. National Cotton Council of America, Memphis, TN, pp. 42±43. Pedersen, M.K., Burton, J.D., Coble, H.D., 1997. Ef®cacy of Finish and its mode of action. In: Dugger, P., Richter, D.A. (Eds.), Proceedings of the Beltwide Cotton Conference, New Orleans, LA, January 7±10, 1997. National Cotton Council of America, Memphis, TN, pp. 1363±1365.
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