Cotton harvest aid efficacy and cotton fiber quality as influenced by application timing

Abstract

Harvest aid chemicals are used to terminate cotton growth and promote boll opening, with optimal application timing recommended at four nodes between the uppermost first position cracked boll and the uppermost first position harvestable boll (4 NACB). However, recommendations rely on data from the southeast and mid-south regions of the Cotton Belt, which may not reflect conditions in much of the southwestern region. Producers in Oklahoma may delay harvest-aid applications until the crop is nearly mature potentially sacrificing fiber quality to weathering, or be in a situation where triggering applications early could allow for optimal harvest aid activity prior to a freeze event. The objectives of this study were to quantify, (1) the relationship between cotton maturity, as determined by the NACB method and the percent of open bolls, (2) the efficacy of boll opening from harvest aid applications made at various maturity levels, as well the amount and response of undersized bolls present at each application timing, and (3) impact of harvest aid application timing on cotton fiber quality. A standard harvest aid mix of tribufos and ethephon was applied at four-to-five-day intervals for three site- years from 2019 to 2020. A non-treated control was included at both locations and site- years. Across all site-years there was a strong relationship between NACB and percentage of open bolls (R2 = 0.85), agreeing with previous findings that 4 NACB generally occurs when approximately 60% of bolls are open. By seven days after application, approximately 80% of harvestable-sized bolls were open regardless of application timing, with no impact on fiber quality. Early application may prevent yield and fiber quality losses if inclement weather is encountered prior to the crop reaching maturity.