Cotton (Gossypium hirsutum) Defoliation As Affected By Droplet Size and Carrier Volume

A field experiment was conducted to evaluate the effect of carrier volume and spray droplet size on the efficacy of cotton (Gossypium hirsutum) harvest aid applications.  This experiment was conducted at the R.R. Foil Plant Science and Research Center in Starkville, Mississippi and at the Black Belt Branch and Experiment Station in Brooksville, Mississippi.  Four row plots were planted to DP 1646 B2XF. Plot dimensions at each location were were 3.9m x 12.2m.  Harvest aid applications were initiated at a threshold of 60% open bolls.

Applications were made with a Capstan® Pinpoint Pulse-Width Modulation (PWM) sprayer on a high-clearance Bowman Mudmaster at a ground speed of 14.5 km hour^-1.  This experiment utilized two carrier volumes: 47 and 187 L ha^-1, three droplet sizes: 200, 500, and 800 µm, and multiple application scenarios: single vs multiple applications.  Harvest aid applications for single (A) applications included: [1] thidiazuron + ethephon and [2] thidiazuron + ethephon + tribufos.  Experimental plots receiving a second application (B) included [A1] + pyraflufen-ethyl + ethephon and [A2] pyraflufen-ethyl + ethephon

Visual ratings were taken at 3, 7, and 10 days after application A (DAA) and B (DAB) and included percent open bolls, percent green leaves, percent defoliation, percent desiccation, terminal regrowth and basal regrowth.  Seed cotton yield data were also collected.  Ratings were taken as a percent (%) relative to the untreated control.  Seed cotton for each plot was sent to the University of Tennessee in Jackson, TN for ginning, and fiber quality was determined by the USA classing office in Memphis, TN. 

Results indicate lower carrier volumes may have utility in cotton harvest aid programs.  In such cases, efficacy may vary due to concentration of active ingredient within the spray droplet.