Field studies were conducted during 1995 to determine the effect of various adjuvants and adjuvant mixtures on the efficacy of Dropp® (thidiazuron) defoliant at 0.1 lb ai/A applied with a conventional boom sprayer at the spray volume of 10 gallons per acre (gpa) and with an air-assist sprayer at the ultra-low volume of one-half gpa. Application was made to cotton plants at 70 to 80% boll opening in plots of four rows each, spaced 40 inches apart, 40 feet long and replicated four times. The adjuvants used were: Agri-Dex®, a non-phytotoxic oil mixed with a nonionic surfactant (83/17, v/v); Dyne-Amic®, an organo silicone based surfactant mixed with a methylated vegetable oil in undisclosed proportions both from Helena Chemical Co.; Impact®, a proprietary blend of polyalkyleneoxide modified heptamethyl trisiloxane and nonionic surfactants from Jay-Mar, Inc.; Silwet 560®, an alkyl modified trisiloxane; Silwet L-77®, a polyalkyleneoxide modified heptamethyltrisiloxane; OSi Blend #1, a blend of methyl soyate 90%, Triton N-57 5% and Silwet 560 5% each from OSi Specialties, Inc. ; and Sun-it II®, a methylated seed oil with proprietary emulsifiers from AGSCO, Inc. The percent defoliation was visually rated at 9 days after application whereby 0 = no defoliation and 100% = complete defoliation of the cotton plants. The least significant difference (LSD) between means as determined by Fisher's Protected LSD test at the 0.05 level was 5%.