1. 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.

2. 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 ( % OB)
Crop with “extended” fruiting (fruit set over several nodes, or a longer time period) may require delayed defoliated ( % OB)

3. 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

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

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

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

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

8. Regrowth
14 DAT
32 DAT

9. Weathering Effects

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

11. 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

12. 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

13. Materials and Methods Standard defoliation treatment :
Tribufos lbs a.i. / A {8 oz/A of product (6 lbs a.i. / gal)}
Thidiazuron 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 = days after defoliation
Delayed Harvest = days after defoliation
Compact
2006
2007
Extended
Early Def 38 34 45 39
Late Def 85 71 79 74

14. Materials and Methods
All mepiquat chloride and defoliation treatments applied with a CO2 backpack sprayer with 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

15. Results

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

17. 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

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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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)

33. Literature Cited
Collins, G.C, K.L. Edmisten, D.L. Jordan, R. Wells, J.E. Lanier, and G.S. Hamm 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 pp.
Edmisten, K.L Cotton defoliation. pp In: 2007 Cotton Information. NC Cooperative Extension Service. 227 pp.
Faircloth, J.C., K.L. Edmisten, R. Wells, and A.M. Stewart Timing defoliation applications for maximum yields and optimum quality in cotton containing a fruiting gap. Crop Science. 44:

34. 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

35. Questions ??