Cotton Response to Planting Date and Mepiquat Chloride

Few studies have documented the effect of planting date on cotton ( Gossypium hirsutum L.) response to mepiquat chloride (MC) ( N,N ‐dimethylpiperidinum chloride). Planting dates were mid‐April, early May, and mid‐May during 1982, 1983, and 1984, and consisted of five cultivars representing three general maturity types: early—‘DES 422’; intermediate—‘Coker 3131’, ‘Stoneville 825’, and ‘McNair 235’; and full season—‘Deltapine 90’. Mepiquat chloride was applied at a rate of 49 g a.i. ha −1 when the plants had about 0.7 white flowers per meter of row. More parameters were affected by chemical treatment and planting date than by cultivars. Plants were taller and produced fewer flowers, smaller bolls, and less lint as planting dates were delayed. In addition, most boll components were adversely affected by delayed planting dates. However, most of the adverse effects caused by delayed planting were mitigated by the MC treatment. Mepiquat chloride x planting date interactions occurred for plant height, flower production, lint yield, and seed index. Mepiquat chloride caused a 4.5% reduction in lint yield from the early planted plots, and 5.4 and 12.7% yield increases from the optimum and late plantings, respectively. Mepiquat chloride increased boll weight in all plantings, but affected (increased) flower production only in the late planting. Seed index was increased and lint percentage reduced in all MC‐treated plots from each of the three plantings. The MC early, intermediate‐, and late‐planting plots averaged 0.11, 0.25, and 0.30 less height, respectively, than the control plots. Statistical significance was achieved only for the latter two plantings. These studies indicate that MC application would be most beneficial in late‐planted cotton, which tends to produce more vegetative growth than earlier plantings.