Extension Cotton Specialists Working Group Presenting: Darrin Dodds

1. Efficacy and Agronomic Impacts of Commercially Available Plant Growth Regulators Across the Cotton Belt Extension Cotton Specialists Working Group Presenting: Darrin Dodds

2. Extension Cotton Specialists Working Group • Clemson University • Mike Jones • University of Tennessee • Chris Main • Texas AgriLife Extension Service • Randy Boman • Robert Lemon • Virginia Tech • Joel Faircloth • University of Arizona • Randy Norton • Mississippi State University • Darrin Dodds • Kansas State University • Stewart Duncan • Auburn University • Charles Burmester • Dale Monks • University of Arkansas • Tom Barber • University of Georgia • Steve Brown • University of Florida • David Wright • University of California – Davis • Bob Hutmacher • Louisiana State University • Sandy Stewart • North Carolina State University • Keith Edmisten • Oklahoma State University • J.C. Banks

3. Cotton Growth Habit • Vegetative and reproductive development occur simultaneously • Vegetative growth necessary to support reproductive growth • Excessive vegetative growth can be detrimental • Excessive vegetative growth: • Increased fruit abortion • Delayed crop maturity • Yield reduction Jost et al. 2006

4. Fruit Abortion • Fruit initiates at bottom of plant and progresses upward and outward (Ritchie et al. 2004) • Excessive vegetative growth can shade the lower canopy and lead to abscission of early fruit (Oosterhuis 2001) • Other factors can contribute to abscission of early fruit

5. Delayed Maturity and Yield • Loss of early fruit may be compensated for when favorable conditions exist • Compensatory growth can result in delayed maturity (Silvertooth et al. 1999) • Yield reductions may occur due to reduced boll size (Jones and Wells 1998)

6. Boll size (g/boll) Main Stem Node

7. Shading of the Lower Canopy • Excessive shading can decrease micronaire of lower bolls (Eaton and Ergle 1954) • Boll rot • Penetration of pesticides

8. What is a Plant Growth Regulator? • Chemicals used to alter the growth of a plant or plant part • Agricultural research with PGRs began in the 1930’s • Acetlyene and ethylene • Enhanced flower production in pineapple Fishel 2006

9. How Do PGR’s Work? • Three types of hormones are affected by foliar applied PGR’s • Gibberellins, Cytokinins, and Auxin Taiz and Zeigler 1998 • Mepiquat reduces the concentration of gibberellic acid in the plant Hake et al. 1991 • Mepiquat only affects new growth

10. Effects of PGR Application • Reduction on total number of mainstem nodes • Reduction in internode length Reddy et al. 1992 • Reduction in leaf area • Shift in boll location

12. PGR Applications and Cotton Yield • Yield response to mepiquat has always been inconsistent Biles and Cothren 2000 • Positive yield effects are more likely to occur when fruit retention is reduced and vegetative growth is excessive Cook and Kennedy 2000 • Yield reductions more likely to occur when excessive rates of mepiquat are applied to stressed cotton

13. Objectives • Examine several commercially available PGRs • Quantify effect of PGR application on height, yield, and fiber quality • Use these data to further refine PGR application recommendations

14. Agronomic Information • Studies were conducted in 19 locations over two years across the cotton belt • Planting date, seeding rate, fertility, insect management, and harvest aid applications were based on extension recommendations for each state • Small plot research techniques were utilized at all locations

15. Varieties Planted

16. Mepex Mepiquat chloride 0.35 lb ai/gal Mepex Gin Out Mepiquat Chloride 0.35 lb ai/gal Kinetin – cytokinin analog Pentia Mepiquat pentaborate 0.82 lb ai/gal Same amount of mepiquat as Mepex Stance Mepiquat chloride Cyclanilide Auxin transport and synthesis inhibitor 0.736 lb mepiquat chloride/gal Plant Growth Regulators

17. *** All PGR treatments included Induce at 0.25 % v/v ***

18. Data Collection • Data collected included: • Plant height prior to initial PGR application • Plant height prior to second PGR application • Plant height two weeks after second PGR application • Plant height at the end of the season • Total nodes • Nodes above cracked boll • Yield • Fiber quality (HVI)

19. Plant Height Prior to 1st App.

21. Plant Height Prior to 2nd App. LSD (0.05) = 0.9 C C C B C C C A A

23. Plant Height 2 Wk After 2nd App. LSD (0.05) = 1.2 D BCD B B BC D A A

25. Final Plant Height LSD (0.05) = 1.5 B B B B B B A A

27. Total Nodes LSD (0.05) = 0.6 B B B B B B A A

29. Nodes Above Cracked Boll LSD (0.05) = NSD

31. Lint Yield LSD (0.05) = NSD

36. Conclusions • All PGR’s examined provided similar plant height reductions • PGR application did not enhance lint yield • Total number of nodes and NACB were similar regardless of PGR applied

37. Conclusions • Mic and uniformity were similar whether a PGR was applied or not • Minor differences in staple length and strength were observed • PGR product selection should be based on individual grower needs as opposed to a specific product • PGR application decisions should be made on a field-by-field basis each year

38. Questions