The Effects of Defoliation Timing and Ethephon Rate on Harvest Date, Lint Yield, and Fiber Quality of Cotton Guy Collins, Keith Edmisten, James Lanier, Gary Hamm, Andrew Hunt, Ranjit Riar, and Matt Schmidt North Carolina State University Raleigh, N.C.

Introduction Typically, cotton defoliation is initiated at approximately 60 % OB Crop with “compact” fruiting (fruit set over fewer nodes, or a shorter time period) can be defoliated earlier (20 - 40 % OB) Crop with “extended” fruiting (fruit set over several nodes, or a longer time period) may require delayed defoliated (70 - 90 % OB)

Previous Work Edmisten, 2007 Faircloth et al., 2004 The authors suggest that defoliation timing can be adjusted for various fruiting patterns and crop conditions Collins et al., 2007 found this to be true, however harvest date was influenced

Lint Yield* A BC CD kg ha-1 *Data pooled over cultivars

Lint Yield* AB BCD D kg ha-1 *Data pooled over cultivars

Lint Yield* A AB BC BCD CD D kg ha-1 *Data pooled over cultivars

Micronaire* A B Units *Data pooled over years, cultivars, and defoliation timings.

Regrowth 14 DAT 32 DAT

Weathering Effects

Fiber Strength* NS A B g tex -1 *Data pooled over cultivars and defoliation timings

Objectives To determine if increasing ethephon rate can promote an earlier harvest if cotton is defoliated early To determine if ethephon rate and/or harvest date has any effect on defoliation efficacy and fiber quality

MC applied according to the Modified Early Bloom strategy Materials and Methods Experiments conducted in 2006 and 2007 at Upper Coastal Plains Research Station near Rocky Mount, N.C. DP 454 BG/RR was planted in a 38-inch row configuration on May 3, 2006 and May 14, 2007 Fruiting pattern Treatment Compact MC applied according to the Modified Early Bloom strategy Extended No MC applied

Materials and Methods Standard defoliation treatment : Tribufos - 0.38 lbs a.i. / A {8 oz/A of product (6 lbs a.i. / gal)} Thidiazuron - 0.1 lbs a.i. / A {3 oz/A of product (4 lbs a.i. / gal)} Ethephon Rates : none 1.5 lbs a.i. / A {32 oz/A of product (6 lbs ai / gal)} 3 lbs a.i. / A {64 oz/A of product (6 lbs ai / gal)} Targeted defoliation timings include : Early = ~ 40 % OB Late = ~ 80 % OB Harvest Timings : Early Harvest = 14 + 2 days after defoliation Delayed Harvest = 28 + 2 days after defoliation Compact 2006 2007 Extended Early Def 38 34 45 39 Late Def 85 71 79 74

Materials and Methods All mepiquat chloride and defoliation treatments applied with a CO2 backpack sprayer with 110-02 flat-fan nozzles, calibrated to deliver 15 GPA Experimental design was a split block / split plot design containing 4 replications Data were subjected to ANOVA (mixed procedure) and means separated using Fisher’s Protected LSD at P < 0.05 Some data are presented by year

Results

Results – Lint Yield Harvest timing by ethephon rate interaction – years combined

Lint Yield* A A A A A B Lbs / A Normal rates of Ethephon promoted an early harvest, however high rates showed no advantage. Ethephon had no effect on yields if cotton was harvested late *Data pooled over years, defoliation timings, and fruiting patterns

Results – Lint Yield Harvest timing by ethephon rate interaction – years combined Ethephon rate by fruiting pattern interaction – years combined

Lint Yield* NS A A B Lbs / A Ethephon promoted higher yields for compact crops, although high rates were not necessary. Ethephon had no effect on yield of the extended fruiting crops *Data pooled over years, defoliation timings, and harvest timings

Lint Yield* NS NS A B Lbs / A When comparing fruiting characteristics, only the high rate of ethephon enhanced yields of the compact crop compared to the extended fruiting crop *Data pooled over years, defoliation timings, and harvest timings

Results – Lint Yield Harvest timing by ethephon rate interaction – years combined Ethephon rate by fruiting pattern interaction – years combined Harvest timing by ethephon rate by fruiting pattern interaction -years combined

Lint Yield* Compact Fruiting A A A AB B B Lbs / A For compact fruiting crops, ethephon promoted an early harvest, although high rates were not necessary. However, high rates of ethephon increased yields if a compact crop was harvested late. *Data pooled over years and defoliation timings

Lint Yield* Compact Fruiting NS NS A B Lbs / A In comparing yields of harvest dates within each ethephon rate, you can see that when no ethephon was used, yields of compact crops increased as harvest was delayed, however both rates of ethephon promoted an earlier harvest for a compact crop *Data pooled over years and defoliation timings

Lint Yield* Extended Fruiting A AB AB AB AB B Lbs / A For extended fruiting crops, higher rates of ethephon decreased yields if harvest was delayed *Data pooled over years and defoliation timings

Results – Micronaire Defoliation timing by ethephon rate interaction – 2007 only

Micronaire* 2007 NS A B B Units In one year of this study, ethephon decreased MIC values if cotton was defoliated early, however ethephon had no effect on MIC if defoliation occurred later *Data pooled over fruiting patterns and harvest timings

Micronaire* 2007 A NS NS B Units Mic was only reduced by later defoliation timings when no ethephon was used *Data pooled over fruiting patterns and harvest timings

Defoliation Efficacy - 2007 7 DAT 14 DAT Defoliation percent increased as ethephon rate increased at 7 days after defoliation, whereas only the high rate showed any substantial advantage at 14 days after defoliation

Plant Mapping – years combined MC treatment Height H N-1 ratio Sympodia Node of 1st Sympodia Sympodial Retention No MC 32.0 A 1.59 A 8.9 A 5.6 B 37.1 B MC applied 26.6 B 1.37 B 7.6 B 6.0 A 49.4 A In both years of this study, there were distinct differences between the MC treatment and the NTC in terms of height, hnr, the number of sympodia, node of 1st sympodia, and sympodial retention

Plant Mapping - 2006 MC treatment Bolls on nodes 4-7 No MC 1.8 B 2.02 1.04 0.58 MC applied 2.5 A 2.17 0.67 0.19 --- NS However, there were few differences in fruiting characteristics between MC treatments. The only difference observed occurred in the number of bolls on nodes 4-7 in 2006, and all other node zones were not affected. There was no effect of MC on fruiting characteristics in 2007

Conclusions Ethephon can promote an earlier harvest, although high rates are not necessary Ethephon may enhance yield for compact crops more so than extended fruiting crops, especially at higher rates If harvest is delayed, higher ethephon rates may increase yields for compact crops and decrease yields for extended fruiting crops Normal ethephon rates may decrease micronaire values if cotton is defoliated early….if defoliation is delayed, ethephon has no effect on micronaire Higher rates of ethephon may slightly improve defoliation efficacy

Future Research Conduct a similar experiment with various cultivars or in environments that respond better to MC treatment Conduct a similar experiment in various environmental conditions (cooler temperatures during the defoliation and harvest season)

Literature Cited Collins, G.C, K.L. Edmisten, D.L. Jordan, R. Wells, J.E. Lanier, and G.S. Hamm. 2007. Defining optimal defoliation timing and harvest timing for compact, normal, and extended fruiting patterns of cotton (Gossypium hirsutum L.) achieved by cultivar maturity groups. Submitted for publication in the World Cotton Research Conference 4. 19 pp. Edmisten, K.L. 2007. Cotton defoliation. pp. 161-180 In: 2007 Cotton Information. NC Cooperative Extension Service. 227 pp. Faircloth, J.C., K.L. Edmisten, R. Wells, and A.M. Stewart. 2004. Timing defoliation applications for maximum yields and optimum quality in cotton containing a fruiting gap. Crop Science. 44:158-164.

Acknowledgements Dr. K.L. Edmisten J.E. Lanier, G.S. Hamm, A.D. Hunt, R.S. Riar, M.C. Schmidt Dr. C. Arellano Cotton Incorporated and the NC Cotton Producers Association

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