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

During September of 2018, field experiments were conducted in Starkville and Brooksville, Mississippi to evaluate the effect of spray droplet size and carrier volume on the efficacy of cotton (Gossypium hirsutum) defoliation applications.  This experiment consisted of three field locations and a single cotton variety, Delta Pine 1646 B2XF, and was defoliated when a threshold of 60% open bolls was achieved.

The experimental design was a 2 x 3 x 4 factorial arrangement of treatments within a completely randomized block design. A single untreated check plot was added to each replication (4), yielding a total of 25 treatment combinations and 100 total plots.

Applications were made at 47 and 187 L ha^-1, and at droplet sizes of 200µm, 500µm, and 800µm.  Chemical treatments included: [1] thidiazuron + ethephon and [2] thidiazuron + ethephon + tribufos applied as an initial ‘A’ application.  A secondary ‘B’ application was made 10 days later and included treatments [3] (1) + pyraflufen-ethyl + ethephon + 1% crop oil and [4] (2) + pyraflufen-ethyl + ethephon + 1% crop oil.  As such, treatments [1] and [2] were applied initially to plots receiving an ‘A’ application only, and as the first application to plots that also received a ‘B’ application.

Ratings included percent green leaf, percent, open boll, percent defoliation, percent desiccation, percent terminal regrowth, percent basal regrowth, and seed cotton yield.  Visual ratings were taken at 0, 3, 7, and 10 days after application ‘A’ (DAA) and after application ‘B’ (DAB).

Additionally, 25 boll boll-samples were taken for ginned on a laboratory micro-gin for fiber quality analyses, and samples sent to the University of Tennessee in Jackson, Tennessee for leaf and color grade analyses.