Cotton Fruiting Modification with Mepiquat Chloride1

Fruiting of cotton (Gossypium hirsutumL.) was evaluated by main stem node and branch position in 11 experiments over a 4‐yr period to determine if mepiquat chloride (MC) (1,1‐dimethylpiperidinium chloride) altered fruiting position development or retention. Fruiting events were monitored for main stem nodes 7 to 20 for first fruiting position on sympodial branches (SB1), secondary fruiting positions on sympodial branches (SB>1), and fruiting positions on monopodial branches (MB). Ten consecutive plants were plant mapped from each of four replications in each experiment and combined as a 40‐plant total for analysis of treatment and node effects using experiments as replications. Mepiquat chloride was applied at 49 g ha−1when average plant height was 0.57 m and plants averaged 0.9 white blooms m−2. Summed across nodes, plant zones SB1, SB>1, and MB accounted for 60, 26, and 13% of all harvestable bolls, produced 37, 46, and 17% of all fruiting positions, and set 45, 16, and 23% of all fruiting positions as harvestable bolls, respectively. Application of MC did not increase total number of bolls. The interaction of MC treatment and nodes was significant for SB1 and SB>1, with MC treated plants setting more bolls at lower nodes but fewer at upper nodes. The maximum cumulative benefit occurred at node 12 where MC treated plants had 15% more bolls matured than control plants (58.3 and 50.6 bolls m−2, respectively). This advantage from MC treatment was not maintained as upper nodes matured fewer bolls than control plants. Plants treated with MC produced 3.1% fewer (P = 0.07) fruiting positions than control plants (288 and 279 m−2respectively). Treatment by node interactions were significant for SB1 and SB>1, with MC increasing fruiting positions up to node 15 at SB1 and up to node 9 for SB>1, but having fewer at the remaining nodes. Early boll load was stimulated by MC. Late season boll load was decreased, apparently not by limited initiation of fruiting positions, but rather by increased abortion of fruiting forms. Use of MC according to the rate and timing of these tests would be of benefit when length of the season is a primary constraint to yield potential. In full‐season, non‐rank cotton, however, the early benefit in boll load is lost.