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

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)

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

Trifloxysulfuron Injury Wilting Discoloration Stunting (York, 2005)

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

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

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?

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

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

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.

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 ) ST 5599 BR cottonseed was planted at a rate of 3 seeds/foot on May 12, 2005 (Rocky Mount, 2005)

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

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

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

Treatments Mepiquat chloride regimes: 14 DAPHS21 DAPHS31 DAPHS none--- 1 app g/ha (8 oz/A) app g/ha (16 oz/A) app 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)

Treatments Additional treatments: 14 DAPHS21 DAPHS31 DAPHS 1Trifloxysulfuron 5.25 g/ha (0.1 oz/A) 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)

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

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

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

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

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

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

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

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 * * * *

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

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

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

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

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 LSD

Boll Distribution – Trifloxysulfuron main effect 1 1 Data pooled over all locations Node ZoneNone 5.25 g/ha 7 DAPHS LSD _________ no. _________ ns ns > ns

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

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 LSD

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

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

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 LSD

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

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

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

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

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 MC B F

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

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

References Norton, E.R., and H.J. Borrego 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 Cotton’s Response to Mepiquat Chloride, Pyrithiobac, and CGA N.C. State University Masters thesis. Griffith, G.M., J.L. Barrentine, M.R. McClelland, and O.C. Sparks Effect of Planting Date on Response of Cotton to Envoke. Summaries of Arkansas Cotton Research. pp

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