Plant Growth Regulator Programs in Arizona Cotton Erin L. Taylor and Patrick A. Clay University of Arizona Cooperative Extension

Introduction Agronomic practices in Arizona cotton production can cause a vegetative growth habit rather than a reproductive one which can lead to decreased yield (Norton et. al., 2006). To control excessive vegetative growth and help maintain a balance between vegetative and reproductive growth PGR’s are often used (Silvertooth, 2001 ).

Control of Vegetative Growth To help maintain a vegetative:reproductive balance mepiquat chloride or mepiquat pentaborate are two common PGR’s used in today’s Arizona cotton production.

Use of Cotton PGR’s Arizona usage 1080 (Arizona Department of Agriculture, Ag. Statistics, University of Arizona) Year Total acreage

Problems with Excessive Vegetation Fruit abortion Decrease in lower boll quality (micronaire) Delayed Maturity –Late boll set Low Yield –Smaller bolls

Feedback vs. Scheduled Feedback –Plant mapping Height:Node ratio (Silvertooth, 2001) Fruit Retention (Silvertooth, 2001) Scheduled –Number of leaves (4-6 leaf stage) –Fruiting Stage Pin head square 1 st bloom

Objectives Evaluate Feedback vs. Scheduled Applications Evaluate New Formulations and Products Evaluate Yield and Lint Quality

Materials and Methods U of A Maricopa Ag Center Dry planted on 20 April 2006 DP 449 BG/RR at 11 lbs/acre Plot size 13.33’ (4-40” rows) by 25’ or 30’ Randomized complete block design with 4 replications Applications made with CO 2 backpack sprayer calibrated to deliver 15 GPA Harvested on 8 November 2006

Materials and Methods PGR I –Mepex 8 oz/A fb16 oz/A (pin head) 16 oz/A (as needed) –Mepex GinOut 4 oz/A fb 8 oz/A fb16 oz/A (4-6) 8 oz/A fb16 oz/A (pin head) 16 oz/A (as needed) –Pentia 8 oz/A fb16 oz/A (pin head) 16 oz/A (as needed) –Stance 2 oz/A fb 2 oz/A (pin head) 3 oz/A (as needed) –Untreated Feedback vs. Scheduled PGR II –Mepex 8 oz/a 14 oz/a –Mepex and DC oz/a & 1 qt/a 14 oz/a & 1 qt/a –DC qt/a –Untreated Check One Application vs. Two Applications Scheduled –First bloom

Data Collected Height Node 1st Fruiting branch Aborts Nodes Above White Flower (NAWF) Nodes Above Cracked Boll (NACB) Yield Lint Quality

PGR I - Plant Heights

PGR I – Lint and Quality Treatment% Lint 1 MicronaireStrength (g/tex) Scheduled Mepex32.02 de b32.70 ab Mepex GinOut31.63 e4.70 ab35.55 ab Mepex GinOut fb Mepex32.43 cde4.70 ab31.70 abc Mepex GinOut31.86 de4.68 ab32.78 a Penita31.81 de4.60 b32.38 ab Stance32.49 cde4.85 ab31.93 abc As Needed Mepex33.47 abc4.75 ab32.28 ab Mepex GinOut33.45 abc4.78 ab32.03 ab Penita33.70 ab4.73 ab32.70 ab Stance33.80 ab4.83 ab30.63 c Untreated check34.28 a4.93 a31.95 abc 1 Yield, fiber length, staple length, and uniformity did not significantly differ. 2 Means followed by the same letter are not significantly different (P=.05, Duncan's New MRT)

PGR II –End of Season Heights

PGR II – Yield and Fiber Characteristics No differences were observed for Yield, % Lint, Micronaire, Fiber Length, Staple Length, or Uniformity

Discussion PGR I In the PGR I trial the only differences observed were % lint, micronaire and strength. % lint showed to be greater in the feedback approach and the untreated control.

Discussion PGR II Height differences were seen throughout the season with no differences in yield. The additive provided no added benefit to the Mepex. The Mepex 16 oz/A rate had an effect on plant height only. No differences were seen in yield and fiber quality.

Acknowledgements Bayer Crop Science DuPont Dune Company Maricopa Ag. Center