Sundance Farms of Coolidge, AZ was the primary study site with DPL 5415 cotton. For the furrow irrigation test, a field was divided into two 15-acre halves. Beauveria bassiana (as Naturalis-L^®) was applied to one half of the field (15 sub-sampling plots, 3 X 5). The synthetic pyrethroids bifenthrin (as Capture^®) and zeta-cypermethrin (as Mustang^®) were applied to the second half (5 and 10 ac, subplots of 1 X 5 and 2 X 5, respectively) as a standard for comparison. For the sub-drip irrigated test, 2 fields were used. In field one, 15 ac were treated with B. bassiana and in the second field, bifenthrin was applied to 5 and zeta-cypermethrin to 10 ac. Sub-plot divisions were similar to the furrow irrigation test.

Label application were used at 25-30 gal/ac applied with a ground sprayer (JD 6000 HI CYCLE) with inverted Y drops on the boom at 70-90 psi. Five applications were made by ground in August and September. All life stages of sweetpotato whitefly (SPWF) Bemisia tabaci were sampled.

For SPWF egg counts in drip-irrigated cotton, mean number/cm² were 0.07, 0.04, and 0.10 for B. bassiana, bifenthrin, and zeta-cypermethrin treatments, respectively. Differences among means were not significant. For SPWF egg counts in furrow-irrigated cotton, mean number/cm² were 4.60, 1.24, and 1.50 for B. bassiana, bifenthrin, and zeta-cypermethrin, respectively; differences between means for drip versus furrow irrigation were significant at P < 0.05. By 2-way ANOVA, the B. bassiana egg mean in furrow irrigation (4.60) was significantly different from all other means at P < 0.001 - interaction.

For SPWF large immature counts in drip-irrigated cotton, mean number/cm² were 0.02, 0.03, and 0.04 for B. bassiana, bifenthrin, and zeta-cypermethrin, respectively; differences among means were not significant. For SPWF large immature counts in furrow-irrigated cotton, mean number/cm² were 0.45, 0.40, and 0.45 for B. bassiana, bifenthrin, and zeta-cypermethrin, respectively; differences between means for drip versus furrow irrigation were significant at P < 0.05. There was no interaction.

For furrow irrigation, mean counts per cm² of large immatures at the end of the season were 6.6, 5.9, 6.9, and 5.9 for B. bassiana, bifenthrin, and zeta-cypermethrin, and a "best agricultural practices field", respectively; differences among means were not significant. However, for an untreated field (received one insecticide treatment-late season) the mean was 41.3 and was significantly different from the other means at P < 0.001. The yields, in bales, for the treated fields were all > 2.8 and was < 2.1 for the untreated field; these differences were significant at P < 0.05.

None of the cotton, neither leaves nor lint showed signs of stickiness in treated plots.

An additional experiment was conducted in small plots at the USDA, ARS Western Cotton Research Laboratory, also with DPL 5415. A split plot design (3 rows X 16 ft) with 5 plots and 4 replicates per treatment received three 5-7 day interval applications of B. bassiana for one treatment and the other was the control. This test was done in September to present a "worst case scenario" in terms of SPWF numbers. For B. bassiana treated plots, mean number of eggs /cm² were 39.11 versus 46.67 for the control plots; means were not significantly different. However, for the mean number of large immatures, 1.33 for B. bassiana treated plots and 3.64, the difference was highly significant at P < 0.001 and represented a percent reduction of 63%.

This work also showed that sub-drip irrigated cotton supported significantly lower populations of SPWF than did furrow-irrigated cotton.