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CROP ECOLOGY, MANAGEMENT & QUALITY

Timing Defoliation Applications for Maximum Yields and Optimum Quality in Cotton Containing a Fruiting Gap

^a LSU AgCenter, Northeast Region, 212-B Macon Ridge Rd., Winnsboro, LA 71295
^b North Carolina State University, P.O. Box 7620, Raleigh, NC 27695
^c North Carolina State University, P.O. Box 7620, Raleigh, NC 27695, Department of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7620
^d LSU AgCenter, Dean Lee Research Station, 8305 East Campus Avenue, Alexandria, LA 71302-9306

^* Corresponding author (jfaircloth{at}agcenter.lsu.edu).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Stresses during cotton (Gossypium hirsutum L.) square and boll formation can result in fruit abscission from several continuous nodes, resulting in a fruiting gap on the plant. This gap may cause a shift in benchmarks for timing various agronomic practices aimed at maximizing cotton yield and optimizing quality. A cotton defoliation timing study was performed in 1999, 2000, and 2001 to (i) see if the creation of a fruiting gap would influence defoliation timing and to (ii) compare the use of the open boll percentage at defoliation (OBPD), nodes above cracked boll (NACB), and micronaire readings at defoliation as tools for timing defoliation. In late July or early August each year, a fruiting gap was created by physically removing fruit from several continuous nodes on plants. Plots were defoliated on the basis of various OBPD values. Upon defoliation, OBPD and NACB were taken and lint was retained to determine the micronaire at defoliation. In both 1999 and 2000, there was a yield advantage to delaying defoliation beyond 60 OBPD in treatments containing a gap. However, in 2001 there was no yield advantage to delaying defoliation. This may have been due to optimal late-season growing conditions experienced in 2001. In years when micronaire readings are high, data suggested cotton not containing a fruiting gap is more likely to be above discount levels for high micronaire and should not be defoliated past 60 OBPD. In both 1999 and 2000, trends confirmed a direct relationship between OBPD and both yield and micronaire. Overall, these studies demonstrated that in some years, where no fruiting gaps exist, it might be possible to terminate cotton before the 60% open boll recommendation without sacrificing yields. These results would allow farmers to shift defoliation, and hence harvest, to a time when there are fewer risks of quality-based discounts. While a significant interaction prohibited the examination of the use of micronaire at defoliation as a technique for timing defoliation, there did not appear to be a significant advantage to using either NACB or OBPD for timing defoliation.

Abbreviations: NACB, nodes above cracked boll • OBPD, open boll percentage at defoliation • UHM, staple length • UI, uniformity index

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
MOST COTTON PRODUCERS routinely terminate cotton development with the aid of defoliants in preparation for harvest. Properly timing defoliation involves balancing the value of potential increases in yield with the value of changes in fiber quality. Barker et al. (1976) found yield decreases resulting from defoliation offset the value of grade improvements and suggested that not defoliating might be an option in some regions. However, the necessity of defoliating cotton varies annually and is determined by numerous factors including growing season, location, cotton market value, and various input costs (Jones et al., 1996; Whitwell et al., 1987). Proper defoliation timing can be critical to yield maximization because delaying defoliation increases risks of yield loss due to damaging early frosts and late season inclement weather, both of which are possible in the North Carolina cotton-growing region. However, delaying defoliation allows immature bolls to develop, thus enhancing yields (Snipes and Baskin, 1994). Defoliation timing also affects various cotton quality characteristics. Eliminating defoliation could result in unacceptable micronaire readings (Kelley and Boman, 1999, 2000) and length and length uniformity can be significantly reduced as a result of either premature (10% open) or normal (60% open) defoliation timing (Laferney et al., 1963).

Numerous stresses (i.e., insect pressure, drought, shading, fertility problems) during square and boll formation can result in fruit abscission (Guinn, 1982). Because a stress frequently occurs over an extended time period, fruit is abscised from several continuous nodes and the result is a fruiting gap. The average boll age and maturity on a plant containing a fruiting gap is at least temporarily reduced. This may ultimately result in reduced yields and inferior quality cotton (Jones et al., 1996; Sheng and Hopper, 1988; Pettigrew, 1994). However, if the growing season is long enough or if fruit abortion occurs early enough in the growing season, cotton has the ability to compensate for the aborted fruit through production of additional mainstem nodes, production of additional fruit in outer positions of fruiting branches and vegetative branches, and the concentration of more resources into remaining reproductive structures (Moss and Bednarz, 1999; Sheng and Hopper, 1988). Thus, yield reductions may not be realized if either abortion occurs early in the season or if the growing season is long enough to allow for adequate boll compensation (Jones et al., 1996; Pettigrew et al., 1992). While the literature is sparse regarding effects of a late season fruiting gap on quality, Jones et al. (1996) reported increases in micronaire readings in cotton containing a late season fruiting gap. The presence of a late season fruiting gap in cotton may require growers to deviate from usual defoliation timing methods.

NACB is a measurement used as a method of timing defoliation where only plants containing a first-position cracked boll are utilized (Kerby et al., 1992). Beginning with the node above the sympodial branch containing the highest first position cracked boll, nodes are counted upward to the node containing the highest harvestable boll. The number of nodes traversed equals the NACB. Kerby et al. (1992) remarked that using the OBPD measurement as a tool for timing defoliation requires knowledge of flowering period length. If the flowering period is short, the crop will be compact and defoliation could occur before 60% open. If the flowering period is extended, however, the bolls will be spread throughout the plant and the plant may need more time to fully develop all bolls, thus early defoliation will not be appropriate. Supak et al. (1993) supported the use of NACB as a means of timing defoliation, provided the crop is uniform in emergence and fruiting initiation and retention are normal. Both researchers report no yield or micronaire changes when cotton is terminated at NACB 3.

Snipes and Baskin (1994) conducted a study where treatments were defoliated after 20, 40, 60, and 80% of the bolls were open and report yield losses and decreases in micronaire resulting from early defoliation. These researchers recommend defoliants be applied after 60% of the bolls are open. Sassenrath-Cole and Hedin (1996) later reported boll opening may be more reflective of boll age rather than maturity, thus, using OBPD as a benchmark for timing defoliation may result in deviations from optimal fiber quality.

This study was designed to test the hypothesis that the existence of a fruiting gap influences optimum timing of defoliation on the basis of yield and fiber quality [micronaire, staple length (UHM), uniformity index (UI), and strength] responses. Additionally, this research was designed to compare NACB, OBPD, and micronaire readings as means of timing defoliation.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The following study was conducted in 1999, 2000, and 2001, on the Central Crops Research Station (CCRS) in Clayton, Johnston Co., NC. Treatments represented two fruiting patterns (presence of a man-made fruiting gap and a control containing no fruiting gap) defoliated at five maturity stages based on a targeted OBPD. These maturity stages were 15, 30, 45, 60, and 85% open. Stoneville 474 (Stoneville Pedigreed Seed, Memphis, TN) was planted on 6 May 1999, 9 May 2000, and 11 May 2001. Plots contained 4 rows spaced 1 m apart. In 1999 and 2000, rows were 15.2 m in length and in 2001 rows were 10.7 m in length. A randomized complete block design with a factorial arrangement of treatments replicated four times was used each year. North Carolina Cooperative Extension guidelines were followed regarding insect control, weed control, and fertility (2000 Cotton Information, 2000).

Temperature and rainfall data were obtained for each year from the Central Crops Research Station. Heat units were calculated by the following equation: [(daily mean high temperature °C + daily mean low temperature °C/2)] – 16°C. Any daily heat unit values less than 0 were treated as 0 for further calculations. Total heat unit accumulation from the time of planting until 1 October, total rainfall accumulation from the time of planting until 1 October, and total rainfall from the day of fruit removal until 1 October were calculated for each year the study was conducted.

Fruit removal was performed on 30 July 1999, 8 Aug. 2000, and 2 Aug. 2001 to mimic fruit loss due to stress (i.e., insect pressure, drought, shading, fertility, etc.). The mean highest position white flower for each plot was measured and sympodial branches 9 through 12 were located relative to this flower's position. Using the highest first position white flower as a guide, all fruit was removed from sympodial branches 9 through 12, leaving several nodes intact above and below the gap. This removal was performed on the third and fourth rows of four row plots. All data was taken from these two rows. Before harvest, standard plant mapping procedures were performed on 10 plants per plot to assess the adequacy of fruit removal and examine possible areas of boll compensation. Data reported include bolls per plant on sympodial nodes 10 and 11, vegetative bolls per plant, bolls per plant on outer positions (past position 2), and total number of bolls per plant in all years except 1999, when the number of vegetative bolls and outer position bolls was not recorded. Proc GLM (SAS Inst., 1997) was used to test for year interactions and treatment effects on all plant parameters measured with year, replicate, and gap type as class variables. All statistical analyses were conducted at the p 0.05 level.

In September of each year, OBPD measurements were taken several times weekly until all plots had been defoliated. Mean OBPD measurements for each plot were calculated by averaging three random samples. Each sample was recorded from five adjacent plants. Bolls on each plant (15 per plot) were examined and recorded as open or closed. These data were used to calculate the mean percentage open. In 1999 and 2001, plots were defoliated when OBPD in a treatment averaged across the four replicates approximated the targeted percent open. Because of field variation in 2000, plots were evaluated and sprayed on an individual basis. In all years, mixtures of Finish (ethephon + cyclanilide) at the 1.68 kg ai ha^–1 rate with Dropp (N-phenyl-N, 1, 2, 3-thiadiazol-5-ylurea) at the 0.08 kg a.i. ha^–1 rate were applied for defoliation while the minimum daily temperature was 13°C. These rates are recommended at these temperatures although the effectiveness declines with temperature. When daily temperatures fell below this point, a mixture of Finish (ethephon + cyclanilide) at the 1.68 kg ai ha^–1 rate, Harvade (2, 3-dihydro-5, 6-dimethyl 1,4 dithiin 1,1,4,4-tetraoxide) at the 0.38 kg ai ha^–1 rate, and Def (S, S, S-tributyl phosphorotrithioate) at the 0.70 kg a.i. ha^–1 rate was used for defoliation.

All defoliation applications were delivered using a CO₂ backpack sprayer with pressure set to 4.22 kg cm^–2. The boom sprayed 2 rows with hollow cone TX-6 nozzles. The sprayers were calibrated for a 4.82 km h^–1 walking speed before each application and chemicals mixed accordingly.

Methods described by Kerby et al. (1992) were followed to record NACB immediately before defoliation in 2000 and 2001. The highest, first position white flower and the highest harvestable boll on the same plant are identified and the number of nodes between these two is the NACB. This measurement was recorded for 10 plants per plot. Additionally, lint from ten bolls per plot was retained at defoliation for high volume instrumentation (HVI) analysis performed by Cotton Incorporated (Cotton Incorporated, Cary, NC). The bolls were randomly selected from open bolls at the time of defoliation. Micronaire readings and NACB values were used for comparison with OBPD as methods of timing defoliation. Rows 3 and 4 from all plots were harvested on 27 October 1999, 29 November 2000, and 7 November 2001 using a two-row, John Deere spindle picker. Approximately 300 g of seedcotton was retained and ginned using a twelve saw table top gin to obtain lint percent. Lint from harvest was also subjected to HVI analysis performed by Cotton Incorporated.

All harvests data including lint yield, micronaire, UHM, UI, and strength were analyzed by Proc GLM, with year, replicate, gap type, and target OBPD as class variables. Where interactions involving year were significant, Proc GLM was run by year with replicate and gap type as class variables and OBPD as a continuous variable, fitting linear and quadratic main effects for OBPD as well as interactions with gap type. Insignificant quadratic effects were eliminated and models were rerun. Additionally, Proc GLM was run by year with gap type as a class variable fitting for OBPD, gap type, and OBPD within gap type to generate regression equations relating yield and micronaire readings from cotton retained at harvest to OBPD for each gap type and compare slopes to 0.

In 2000 and 2001, data were used to compare the use of NACB, micronaire readings taken at defoliation, and OBPD for timing defoliation. Yield was analyzed by Proc GLM with year, replicate, gap type, and the target OBPD as class variables with the method of timing (NACB, micronaire readings taken at defoliation) as a continuous variable. Similar to the analyses with OBPD as a continuous variable, when interactions were significant, Proc GLM was run for each year with gap type and replicate as class variables and linear and quadratic terms for methods of timing defoliation.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Fruit Removal
Interactions with year were insignificant for all plant mapping parameters measured; therefore, these data were pooled over years. The number of bolls per plant on nodes 10 and 11 give statistical evidence that the removal treatments resulted in a fruiting gap (Table 1). As anticipated, the number of bolls on vegetative branches and sympodial branch outer positions was lower on plants without a fruiting gap, although this difference was only numerical. On plants without a fruiting gap, the total number of bolls was numerically higher.

In 1999, slopes fitting yield across OBPD for each gap type (Fig. 1) were different as the OBPD by fruiting gap type interaction was significant (Table 2). The OBPD main effect was also significant. Yield in the treatment containing a fruiting gap increased with OBPD and the slope was significantly different from 0, whereas the slope was not significantly different from 0 when no gap was present.

View larger version (28K): [in this window] [in a new window]   Fig. 1. Relationship between yield and time of defoliation based on various open boll percentages at defoliation (OBPD) for each gap type in 3 yr at Clayton, NC. Each data point represents yield at a particular OBPD in an individual plot. * Slope of the gap and no gap treatments for that year are significantly different from each other. Fisher's Protected LSD, p 0.05.

In 2001, OBPD was the only significant effect (Table 2). Thus, yields averaged over gap types were positively related to OBPD. As the gap type main effect and the OBPD by gap type interaction were both insignificant, there was no yield advantage to delaying defoliation on the basis of the presence of a fruiting gap (Table 2). There was a small range in yield values in 2001 relative to 1999 and 2000 and regressions revealed little concerning gaps on the plant (Fig. 1). However, the slope of the regression fitting yields across OBPD for gap treatments in 2001 was not significantly different from 0 and the slope of the regression fitting yields across OBPD for treatments not containing a fruiting gap was significantly different from 0.

Fiber Quality
Because of a significant year x gap type interaction in the model for micronaire, each year was analyzed separately. In 1999 and 2000, gap type and OBPD main effects were significant (Table 2) as overall micronaire values averaged across gap types increased with OBPD values and micronaire values in treatments containing a fruiting gap were lower than those in treatments not containing a fruiting gap (Fig. 2). Gap type x OBPD interactions was not significant in either year. In 1999, the slope of the relationship between micronaire and OBPD for gap and no gap treatments was significantly different from 0. In 2000, the slope of the relationship between micronaire and OBPD for treatments containing a gap was not significantly different from 0 and the slope for treatments not containing a gap was significantly different from 0 (Fig. 2).

View larger version (26K): [in this window] [in a new window]   Fig. 2. Relationship between micronaire and time of defoliation based on various open boll percentage at defoliation (OBPD) for each gap type over 3 yr at Clayton, NC. Each data point represents micronaire values from at a particular OBPD measured in an individual plot at harvest. * Slope of the gap and no gap treatments for that year are significantly different from each other. Fisher's Protected LSD, p 0.05.

The effect of fruiting gap on strength was significant in both 1999 and 2000 although results were inconsistent (data not shown). There were no differences in strength for any effects tested in 2001. Other than overall differences in UHM and UI values each year, there were no significant treatment effects (data not shown).

Methods of Timing Defoliation
Quantitatively, all methods of timing defoliation could not be compared because of a significant interaction between micronaire taken at defoliation and gap type in 2001 (Table 3). However, these data were used to compare NACB and OBPD methods of timing defoliation and there did not appear to be a significant advantage to using either technique.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Yield data from 2000 and 2001 suggest cotton containing a fruiting gap may require delaying defoliation until more bolls open to achieve yields similar to cotton not containing a fruiting gap. Additionally, delaying defoliation would allow an increase in micronaire value to an acceptable range in a year where overall micronaire is low. However, the discount penalty due to low micronaire currently is approximately half that for high micronaire and historically less common in North Carolina (Edmisten and Faircloth, 2001).

Overall yields in 1999 (grand mean of all plots = 776 kg lint ha^–1) were lower than 2000 and 2001 and the importance of delaying defoliation in treatments containing a fruiting gap was greater. Weather data suggest environment was an important contributor to reduced yields in 1999 (Table 4). Despite relatively high cumulative heat units and overall rainfall from planting until 1 Oct. 1999, North Carolina experienced Hurricane Floyd in September and rainfall accumulation from the time of fruit removal (30 July 1999) to 1 Oct. 1999 was 533- of the 686-mm accumulated throughout the season. In 26 d during September 1999, 432 mm of rainfall accumulated. Excessive rainfall resulted in substantial boll rot, particularly toward the base of the plant leaving plants containing the induced fruiting gap in the middle of the plant completely devoid of fruit with the exception of the uppermost portion of the plants. Thus, in cotton containing a fruiting gap in 1999, any additional yield produced late in the season represented a relatively high proportion of overall yields and increased the importance of delaying defoliation. In 2000 and 2001, both growing conditions and overall yields (1212 kg lint ha^–1 and 1340 kg lint ha^–1 in 2000 and 2001, respectively) were similar to each other. Because temperatures and rainfall from planting to 1 October were adequate in both years and late season weather was less harsh than 1999, overall yields were higher and timely defoliation was of less importance.

On the basis of yields and micronaire, defoliation timing benchmarks can shift with the fruiting pattern of cotton. Producers have to balance the value of the additional yields with risks associated with delaying defoliation (i.e., high micronaire, yield losses due to adverse weather conditions).

Received for publication October 31, 2002.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

• Barker, G.L., C.S. Shaw, K.E. Luckett, and F.T. Cooke, Jr. 1976. Effects of defoliation, plant maturity, and ginning setup on cotton quality and value in the midsouth. United States Department of Agriculture, Agricultural Research Service. ARS-S-120.
• Edmisten, K.L., and J.C. Faircloth. 2001. The 2000 cotton crop. Carolina Cotton Notes 01–3a. http://www.cropsci.ncsu.edu/ccn/2001/ccn-01-1.htm.
• Edmisten, K.L., et al. (ed.) 2000. Cotton Information. North Carolina Cooperative Extension Service. North Carolina State University.
• Guinn, G. 1982. Causes of square and boll shedding in cotton. USDA Tech. Bull. 1672. p. 1–22. U.S. Gov. Print. Office, Washington, DC.
• Jones, M.A., R. Wells, and D.S. Guthrie. 1996. Cotton response to seasonal patterns of flower removal: I. Yield and fiber quality. Crop Sci. 36:633–638.[Abstract/Free Full Text]
• Kelley, M., and R. Boman. 1999. High plains harvest-aid application timing studies. p. 606–607. In Proceedings of the Cotton Beltwide Cotton Conference, Orlando, FL. 3–7 Jan. 1999. National Cotton Council of America, Memphis, TN.
• Kelley, M., and R. Boman. 2000. Harvest- aid combination and application timing effects on lint yield and quality of fiber and seed. p. 702. In Proceedings of the Cotton Beltwide Cotton Conference, San Antonio, TX. 6–9 Jan. 2000. National Cotton Council of America, Memphis, TN.
• Kerby, T.A., J. Supak, J.C. Banks, and C. Snipes. 1992. Timing defoliations using nodes above cracked boll. p. 155–156. In Proceedings of the Beltwide Cotton Conference. Nashville, TN. 6–10 Jan. 1992. National Cotton Council of America, Memphis, TN.
• Laferney, P.E., R.A. Mullikin, and W.E. Chapman. 1963. Effects of defoliation, harvesting, and ginning practices on micronaire reading, fiber properties, manufacturing performance, and product quality of El Paso area cotton, season 1960–1961. United States Department of Agriculture, Agricultural Research Service. Marketing Research Report No. 690.
• Moss, J.M., and C.W. Bednarz. 1999. Compensatory growth after early season fruit removal in cotton. p. 524. In Proceedings of the Beltwide Cotton Conference, Orlando, FL. 3–7 Jan. 1999. National Cotton Council of America, Memphis, TN.
• Pettigrew, W.T., J.J. Heitholt, and W.R. Meredith, Jr. 1992. Early season floral bud removal and cotton growth, yield, and fiber quality. Agron. J. 84:209–214.[Abstract/Free Full Text]
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• Sassenrath-Cole, G., and P.A. Hedin. 1996. Cotton fiber development: Growth and energy contents of developing cotton fruit. p. 1247–1251. In Proceedings of the Beltwide Cotton Conference, Nashville, TN. 9–12 Jan 1996. National Cotton Council of America, Memphis, TN.
• Sheng, S.F., and K.R. Hopper. 1988. Cotton development, yield, and quality after early square removal with ethephon. p. 121–123. In Proceedings of the Beltwide Cotton Conference, New Orleans, LA. 3–8 Jan. 1988. National Cotton Council of America, Memphis, TN.
• Snipes, C.E., and C.C. Baskin. 1994. Influence of early defoliation on cotton yield, seed quality, and fiber properties. Field Crops Res. 37:137–143.
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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Faircloth, J. C. Articles by Stewart, A. M. Search for Related Content PubMed Articles by Faircloth, J. C. Articles by Stewart, A. M. Agricola Articles by Faircloth, J. C. Articles by Stewart, A. M. Related Collections Cotton Other Fiber Crops Other Oil Crops Production Agriculture