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

In 2018, 2019, and 2020, a field experiment was conducted to evaluate the impact of carrier volume and spray droplet size on the efficacy of cotton (Gossypium hirsutum) defoliation programs.  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.  Eight-row (7.7m x 12.1m) plots were planted to DP 1646 B2XF. Initial harvest aid applications were made at 60% open boll, and secondary applications to select plots occurred 10 days later.

Applications were made with a Capstan^® Pinpoint Pulse-Width Modulation (PWM) sprayer on a high-clearance Bowman Mudmaster at a speed of 14.5 km hour^-1.  This experiment utilized two carrier volumes: 47 and 187 L ha^-1, and three droplet sizes: 200 µm, 500 µm, and 800 µm.  Defoliation materials included: thidiazuron (TakeDown^® SC) applied at 0.15 kg ha^-1, ethephon (BollBuster^®) applied at 1.5 kg ha^-1, tribufos (Folex^® 6EC) applied at 0.37 kg ha^-1, and pyraflufen-ethyl (ET^®) applied at 0.105 kg ha^-1.  Defoliation programs included: [1A] thidiazuron + ethephon and [1B] thidiazuron + ethephon + tribufos, [2A] 1A + pyraflufen-ethyl + ethephon, and [2B] 1B + pyraflufen-ethyl + ethephon.

Visual ratings were taken at 3, 7, and 10 days after application (DAT) for both A and B applications, and included open bolls, green leaves, defoliation, desiccation, and terminal and basal regrowth.  All ratings were normalized to the non-treated control. The center two rows were mechanically using a spindle picker modified for plot research., and seed cotton samples for each plot (4.5 kg) were sent to the University of Tennessee in Jackson, TN for ginning.  Fiber quality was determined by the USA classing office in Memphis, TN.