Experiments were conducted with azadirachtin as the product Bollwhip™ against the silverleaf whitefly (SLWF). The effects of azadirachtin on beneficial arthropods and on Lygus plant bugs were studied also. In 1997, Deltapine^® 5415 was planted and furrow irrigated in plots 192.5 ft. in length and 6 rows across (40-in. rows). Two fallow skip rows and 8 ft. alleys separated plots of 0.09ac each. In 1998, Deltapine^® NuCOT 33^B was planted and furrow irrigated in plots 109 ft. in length and 12 rows across (40-in. rows). Four fallow skip rows and 20 ft. alleys separated plots of 0.1 ac each. Bollwhip™ was used in a 4.5% formulation. In 1997, it was used at 3 rates: 3, 6, and 9 oz product /ac The treatments were part of 16-treatment random block design that included a "best agricultural practice regime", a water-treated control, and an adjacent 1-ac block control. In 1998, Bollwhip™ was used at 6 oz product/ac These treatments were part of a 12-treatment random block design that included a "best agricultural practice regime", an embedded control, and an 1-ac block control. Eggs, small nymphs, and large nymphs were sampled from leaves taken from 5 plants per plot, from the fifth main-stem leaf down from the first expanded terminal leaf. Each sample was counted from a 1-in. disk taken between the main leave stem and the next lateral vein. Adults were sampled from 30 leaves/plot, same location using a binomial decision of counting a leaf as positive if 3 or more adults were present. Weekly sweeps were taken in all plots for predators, parasites, and Lygus. Applications were made by ground with 3 nozzles/row; 1 overhead, and 2 with swivel nozzles angled upward on drops. Sprays were applied at 80 psi and 30 gal./ac In 1997, Bollwhip™ was effective at controlling silverleaf whiteflies at all three levels used. The seasonal mean reduction for 8-weekly applications was better than 5-fold less eggs, 4-fold less small nymphs, and 3-fold less large nymphs, than for the block control (all significant at P<0.0001, ANOVA). Yield was excellent and large bolls with non-sticky cotton were produced. In 1998,cotton growth in central Arizona was atypical. The spring was wet, June temperatures were below average, cotton grew slowly (about three weeks late by July), and the SLWF populations increased very gradually. The SLWF action threshold was reached on Aug. 5. Bollwhip™ and Applaud™ (different treatment plots) were applied at that time. Immature SLWF populations peaked on August 9 and never recovered. Immature SLWF populations in Bollwhip™ plots were consistently lower than in the embedded control plots, but were significantly lower at P< 0.05 only for the mean number of eggs. In two years of study with the biorational pesticide, azadirachtin, cotton under treatment with Bollwhip™ had productive yields and was not sticky in a good production year. In a poor production year, we showed that a single application of Bollwhip™ or Applaud™ had similar efficacies against immature SLWF. Bollwhip™ is EPA registered and should have a place in IRM/IPM programs. Progress was also made with ground application technology by achieving spray pressures of 250 psi with spray components for booms that were "off-the-shelf " parts and readily available from spray equipment dealers.