Transgenic, herbicide-resistant cotton and recently commercialized equipment to spindle-pick 38-cm rows have renewed interest in narrow-row cotton production. Published research relative to mepiquat chloride (MC) use requirements for cotton in 38-cm rows is limited. An experiment was conducted at five locations in North Carolina during 2004 and 2005 to determine if MC application strategies currently recommended for wide-row cotton are valid for cotton planted in 38-cm rows. Cotton planted in 38- and 97-cm rows received MC in three application strategies. The low rate multiple (LRM) strategy consisted of MC at 12 g a.i. ha-1 applied three times at 2-wk intervals beginning at the first square stage. The modified early bloom (MEB) strategy consisted of MC at 24 g ha-1 applied 2 wk prior to early bloom (EB) and repeated at EB. The EB strategy consisted of MC at 24 g ha-1 applied at EB and repeated 2 wk later. Cotton in 38- and 97-cm rows responded similarly to MC, as indicated by lack of a significant MC application strategy by row spacing interaction for plant height, fruiting characteristics, fruit retention, lint yield, and fiber quality. Cotton in 38-cm rows was shorter, produced more bolls per unit area, had greater boll retention on first position sympodial sites, and produced 10% more yield than cotton in wide rows. Except for plant height, which was reduced more by MC in the LRM and MEB strategies than in the EB strategy, cotton response was similar with each MC application strategy. Averaged across row spacings, MC increased lint yield 5%. Minor increases in fiber length were noted in cotton treated with MC, but MC did not affect micronaire, fiber strength, or fiber length uniformity. The results indicate current MC recommendations for wide-row cotton in North Carolina are appropriate for cotton in 38-cm rows. The LRM or MEB strategies would be preferred.
