1. Interaction of Trifloxysulfuron (Envoke) and Mepiquat Chloride on Growth and Lint Yield of Cotton Guy Collins, Alan York, Keith Edmisten, Rick Seagroves, Ranjit Riar, Jamie Hinton, James Lanier, Gary Hamm, and Andrew Hunt N.C. State University

2. Introduction Trifloxysulfuron (Envoke ® ) is a broad-spectrum herbicide used to control broadleaf weeds and sedges in cotton (Gossypium hirsutum L.) Postemergence (over-the-top) applications at rates of 5.25 to 7.9 g a.i./ha (0.1 to 0.15 oz/A) beginning at the 5-leaf stage Post-directed applications at rates of 7.9 to 13.1 g/ha (0.15 to 0.25 oz/A)

3. Introduction Postemergence applications are typically delayed until the 7- to 8-leaf stage, due to the greater tolerance of larger plants Trifloxysulfuron typically causes injury, reduces height, and shortens internodes on cotton (Casteel et al., 2004) End-results of trifloxysulfuron applications appear to be similar to the effects of mepiquat chloride

4. Trifloxysulfuron Injury Wilting Discoloration Stunting (York, 2005)

5. Trifloxysulfuron Effects on Plant Height Shortened internodes and reduced height (York, 2005)

6. Mepiquat Chloride Effects on Plant Height Shortened internodes (Edmisten, 2004) Reduced height (Edmisten, 2006)

7. Introduction Can these products be tank-mixed? Should growers reduce rates of mepiquat chloride on cotton receiving trifloxysulfuron? Could mepiquat chloride be eliminated if trifloxysulfuron is used?

8. Previous Work Casteel et al., 2004 – found that trifloxysulfuron and mepiquat chloride had similar effects on plant growth, and suggests that tank-mixing may not be feasible Griffith et al., 2004 – found that 2x rates of trifloxysulfuron decreased the no. of nodes, delayed maturity, and decreased lint yields Norton and Borrego, 2006 – found decreased lint yield by combining mepiquat chloride with trifloxysulfuron, but minor effects on plant growth

9. Objectives To determine if mepiquat chloride rates can be reduced or eliminated if trifloxysulfuron is used To determine if trifloxysulfuron can be tank-mixed with mepiquat chloride, while maintaining adequate plant growth and yields To determine if delaying trifloxysulfuron or mepiquat chloride applications could offset the risks of excessively inhibiting plant growth and compromising yields

10. Hypothesis We hypothesized that mepiquat chloride rates could be reduced if trifloxysulfuron was previously applied, and that delaying applications of trifloxysulfuron may allow plants to form adequate fruiting sites, therefore avoiding yield losses.

11. Materials and Methods Replicated field experiments were conducted in 2005 and 2006 at: Upper Coastal Plains Research Station (Rocky Mount, N.C. – 2005 and 2006) Central Crops Research Station (Clayton, N.C. - 2006) ST 5599 BR cottonseed was planted at a rate of 3 seeds/foot on May 12, 2005 (Rocky Mount, 2005)

12. Materials and Methods ST 5599 BR cottonseed was planted at a rate of 3.5 seeds/foot on May 2, 2006 (Rocky Mount, 2006) ST 5007 B2RF cottonseed was planted at a rate of 3 seeds/foot on May 3, 2006 (Clayton, 2006) Weed control: Glyphosate (Roundup Weathermax) 1.61 L/ha (22 oz/A) at the 1-leaf and 4-leaf stages S-Metolachlor (Dual Magnum) 1.4 L/ha (1 pt/A) at the 4-leaf stage

13. Experimental Design and Treatments Experimental Design = RCBD Treatments: - 2 Trifloxysulfuron rates - 5 Mepiquat chloride regimes Treatments were arranged in a 2 x 5 factorial design

14. Treatments Trifloxysulfuron rates: None 5.25 g/ha (0.1 oz/A) at 7 DAPHS (days after pin-head square)

15. Treatments Mepiquat chloride regimes: 14 DAPHS21 DAPHS31 DAPHS none--- 1 app.--- 25 g/ha (8 oz/A) --- 1 app. --- 49 g/ha (16 oz/A) --- 2 app. --- 25 g/ha (8 oz/A) 37 g/ha (12 oz/A) 3 app. 18 g/ha (6 oz/A) 25 g/ha (8 oz/A) 37 g/ha (12 oz/A)

16. Treatments Additional treatments: 14 DAPHS21 DAPHS31 DAPHS 1Trifloxysulfuron 5.25 g/ha (0.1 oz/A) --- 2 Trifloxysulfuron 5.25 g/ha (0.1 oz/A) --- Mepiquat Chloride 18 g/ha (6 oz/A) 25 g/ha (8 oz/A) 37 g/ha (12 oz/A)

17. Materials and Methods All treatments were applied using a CO 2 -pressurized backpack sprayer calibrated to deliver 140.3 L/ha (15 GPA) All other agronomic practices were conducted according to North Carolina Cotton Extension recommendations

18. Data Collection Plant heights at 36 and 48 DAA (Days after trifloxysulfuron application) Percent open bolls in mid September Plant heights and plant mapping in mid September Seed cotton yields Lint percentage and HVI fiber quality

19. Statistical Analysis SAS version 9.1.3 General Linear Model (Proc GLM) Means separated using Fisher’s Protected LSD at α = 0.05

20. Statistical Analysis Due to power of the factorial arrangement, analysis of factorial treatments are reported separately from the additional treatments Additional treatments were analyzed in a separate 2 x 3 factorial arrangement to compare the effects of trifloxysulfuron application timing (7 and 14 DAPHS) and the non-treated control A mean separation was used to determine if mepiquat chloride rates can be reduced if trifloxysulfuron was previously used Due to strong interactions between some factors and locations, and consideration of F-tests, some data will be presented with locations 1 & 2 combined, and location 3 separately

21. Results Factorial treatments (no interactions between mepiquat chloride and trifloxysulfuron were significant) - Data are pooled over all locations unless otherwise specified

22. Plant Height – Mepiquat main effect 1 A LSD = 2.65 cm 1 Data pooled over all locations LSD = 3.6LSD = 4.06 BC AB C C C C C C C A B A B

23. Bolls/Plant – Mepiquat main effect 1 A LSD = 0.92 No. 1 Data pooled over all locations LSD = 1.08 AB B B A B

24. Aborts/Plant and Retention– Mepiquat main effect 1 LSD = 1.32 No. 1 Data pooled over all locations *Denotes significance at p<0.05 % LSD = 2.65 A B B B B * * * *

25. Total Nodes and H/N Ratio– Mepiquat main effect 1 A LSD = 0.49 No. 1 Data pooled over all locations LSD = 0.27 B B B B A B BC C

26. Position 1 Bolls – Mepiquat main effect 1 A AB A B LSD = 0.699 No. 1 Data pooled over RM2005 and RM2006

27. Lint % - Mepiquat main effect 1 A BC B B C LSD = 0.677 Lint % 1 Data pooled over RM2005 and RM2006

28. Plant Height – Trifloxysulfuron main effect 1 1 Data pooled over all locations *Denotes significance at p<0.05 * * * LSD = 1.67LSD = 2.27 LSD = 2.57 cm

29. Retention, Nodes, and H/N Ratio – Trifloxysulfuron main effect 1 1 Data pooled over all locations Trif. Rate Sympodial Retention Nodes Height/Node Ratio _____ % __________ no. _____ none52.1 A16.8 B4.8 A 5.35 g/ha 7 DAPHS 49.9 B17.3 A4.3 B LSD1.70.30.2

30. Boll Distribution – Trifloxysulfuron main effect 1 1 Data pooled over all locations Node ZoneNone 5.25 g/ha 7 DAPHS LSD _________ no. _________ 4-74.134.00ns 8-104.023.720.26 11-132.222.28ns 14-160.720.950.18 >160.030.00ns

31. Lint Yields – Trifloxysulfuron main effect 1 A B A A RM05 & RM06 LSD = 68.9 Kg/ha 1 Data pooled over RM2005 and RM2006, CL06 separately CL06 LSD = ns

32. Sympodial Bolls/Plant and Nodes – Trifloxysulfuron main effect 1 1 Data for CL06 only Trifloxysulfuron Rate Sympodial bolls Total nodes ___________ no. __________ none6.8 B16 B 5.35 g/ha 7 DAPHS 7.4 A16.5 A LSD0.550.44

33. Results Additional treatments (2 x 3 factorial used to determine the effect of application timing of trifloxysulfuron - no interactions between mepiquat chloride and trifloxysulfuron were significant) - Data is pooled over all locations unless otherwise specified

34. Plant Height 1 1 Data pooled over all locations *Denotes significance at t<0.05 between the NTC and other treatments * * * LSD = 2.34LSD = 2.21 LSD = 4.14 cm

35. Total Nodes and H/N Ratio 1 1 Data pooled over all locations TreatmentTotal NodesH/N ratio _____ cm __________ no. _____ NTC16.9 B4.96 A Trifloxysulfuron 7 DAPHS 17.6 A4.58 B Trifloxysulfuron 14 DAPHS 17.5 A4.46 B LSD0.50.27

36. Bolls/Plant by Node Zone 1 LSD = ns No. 1 Data pooled over all locations LSD = ns

37. Total Bolls/Plant 1 LSD = ns No. 1 Data pooled over all locations

38. Lint Yield 1 LSD = ns Kg/ha 1 Data pooled over all locations

39. Results Mean separation (to determine if mepiquat chloride rates can be reduced if prior trifloxysulfuron was used) - Data is pooled over all locations

40. Plant Height 1 cm 1 Data pooled over all locations LSD = 5.77 A AB C DE D DEF DE DEF EF Trif. 14 Trif. 14 + MC B F

41. Lint Yield 1 Kg/ha 1 Data pooled over all locations LSD = 111.6 A ABC A BC A C ABC AB A ABC C Trif. 14 Trif. 14 + MC

42. Conclusions The behavior of trifloxysulfuron and mepiquat chloride are independent from each other Trifloxysulfuron and mepiquat chloride have similar effects on plant growth and fruiting characteristics – yield response is variable No evidence suggests that delaying the application of trifloxysulfuron helps avoid risks associated with stunting Some evidence suggests that mepiquat chloride rates can be reduced if trifloxysulfuron is used Growers should avoid using trifloxysulfuron on cotton that is stressed or in fields that have a history of early season stress

43. References Norton, E.R., and H.J. Borrego. 2006. Evaluation of Envoke by Pix Interaction in Arizona Cotton Production Systems. Arizona Cotton Report (P-145). Casteel, S.N., K.L. Edmisten, R. Wells, J. Wilcut, J. Spears, and J. Burton. 2004. Cotton’s Response to Mepiquat Chloride, Pyrithiobac, and CGA 362622. N.C. State University Masters thesis. Griffith, G.M., J.L. Barrentine, M.R. McClelland, and O.C. Sparks. 2004. Effect of Planting Date on Response of Cotton to Envoke. Summaries of Arkansas Cotton Research. pp. 200-203.

44. Questions ??