Cotton Cultivar Response to Mepiquat Chloride1

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Abstract
The effects of mepiquat chloride (1,1‐dimethylpiperidinium chloride) on cotton (Gossypium hirsutum L.) growth and yield have been widely studied but few studies have investigated cultivar response to this plant growth regulator. Since the response to a pesticide or a plant growth regulator may vary among cultivars, a knowledge of cultivar response to that chemical is an important consideration when developing recommendations for its use. A 3‐year study was conducted in eight environments to determine if 14 cultivars respond differently to mepiquat chloride. Cultivars evaluated were ‘Coker 304’, ‘Coker 310’, ‘Coker 315’, ‘Coker 420’, ‘Deltapine 41’, ‘Deltapine 55’, ‘Deltapine 70’, ‘McNair 220’, ‘McNair 235’, ‘Rex 713’, ‘SC 1’, ‘Stoneville 213’, ‘Stoneville 506’, and ‘Stoneville 825’. Mepiquat chloride at a rate of 49 g/ha increased lint yield 10 to 28% in three environments and decreased yield 5% in one environment. Earlier maturity was usually observed. Plant height was reduced 11 to 26%, and reductions in plant height were closely correlated with final height of the untreated cotton. Mepiquat chloride increased both boll weight and seed weight 3 to 10%, and slightly increased fiber length. The effect on micronaire was variable, but in most environments there was a small reduction. There was little to no effect on number of seed per boll, fiber strength, and fiber length uniformity. Lint percent was decreased 0.4 to 0.8% in most environments as a result of the increased seed weight. There were no mepiquat chloride by cultivar interactions for lint percent, fiber length, boll weight, seed weight, number of seed per boll, number of bolls produced, plant height, or maturity. Cultivar by mepiquat chloride interactions for yield, micronaire, fiber strength, and fiber length uniformity were observed in only one environment. All observed mepiquat chloride by cultivar interactions were small and, considering the infrequency of occurrence, were probably not of practical significance. This study indicated that cultivar selection should not be a consideration in deciding whether to apply mepiquat chloride.

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