Water Volume and Deposition Effects on Harvest-Aid Efficacy

Harvest aids provide cotton farmers with the ability to harvest in an efficient and timely manner. Harvest aids also assistant in preserving overall fiber quality by reducing fiber degradation and discoloration from exposure to weather and by the reduction of foreign matter. Many harvest-aid active ingredients do not translocate within the plant, thus adequate spray coverage is recommended to improve efficacy of these products. The widespread and rapid adoption of auxin-tolerant cotton varieties has increased the use of larger droplet size nozzles that are required for use with auxin herbicides. Subsequently, the use of larger droplet size nozzles for harvest-aid applications will likely increase. The objective of this study was to determine the impact of droplet size and carrier volume on defoliation, desiccation, boll opening, terminal and basal regrowth, and cotton leaf grade. Varying water volumes of 47, 93, 140, and 187 L ha-1, and nozzles that produced fine, medium, and ultra-coarse droplets were evaluated at 14 site years across the Cotton Belt in 2016 and 2017. Numeric trends indicate higher carrier volumes are more successful at defoliating and opening bolls than lower carrier volumes. Water volumes of 47 L ha-1 should be avoided when making cotton harvest-aid applications, as all defoliation, open boll, and regrowth values were consistently reduced at the lowest carrier volume. Treatments of various nozzle types had less impact on harvest-aid efficacy than carrier volume. Site interactions with harvest aids had a greater effect than nozzle type or water volume.