Chemical defoliation is a necessary pre-harvest practice in Pima cotton (Gossypium barbadense L.) production in the San Joaquin Valley of California. Cotton growers are advised to begin defoliation as early as possible with both Pima and Upland cotton, but not so early that it results in yield and quality loss Potentially harvestable bolls often fail to reach full maturity due to the recommended defoliation timing. Applying harvest aids before the recommended maturity can advance the start of harvest, avoiding late-season pests and adverse weather that can damage lint quality. The objective of this research was to compare different rates of Ginstar® (thidiazuron/diuron, Research Triangle Park, NC) or Ginstar plus Finish® (ethephon/cyclanilide, Research Triangle Park, NC) on defoliation, yield, and fiber quality of Pima cotton when applications began at an earlier timing, six to seven NACB (nodes above cracked boll), versus the common four to five NACB timing. ‘Delta Pine DP-340’ (Monsanto Company, St. Louis, MO) was treated with harvest aid materials in field trials and was analyzed as a factorial split-plot design with four replications. Starting the defoliation of Pima at six to seven NACB rather than four to five NACB brought about a potential seven to ten day earlier harvest and did not significantly affect yield or cotton fiber quality characteristics except for micronaire in one year of the study. These data indicate that earlier defoliation could be beneficial when later-maturing crops or worsening harvest-season weather necessitate the initiation of an earlier harvest.
