Experiments were conducted using oat in the greenhouse to determine phytotoxicity and spray deposit characteristics of sethoxydim on oat as influenced by adjuvants, ultraviolet (UV) light, and temperature at and shortly after application. Petroleum oil of low viscosity was equal or more effective with sethoxydim when applied at 10 than at 25 C, but high-viscosity petroleum oil was more effective at 25 than at 10 C. UV light reduced sethoxydim efficacy more for high- than low-viscosity petroleum oil adjuvant at 25 C, but not at 10 C. Commercial vegetable oil adjuvant was less effective with sethoxydim at 10 than at 25 C, and UV light reduced efficacy at both temperatures. Commercial methylated vegetable oil was the most effective adjuvant and efficacy was only slightly reduced by UV light at 25 C. A secondary alcohol surfactant that is considered hydrophilic enhanced sethoxydim efficacy even when exposed to UV light. Adjuvants that gave discernible uniform spray deposits with close contact to the epicuticular surface, including over anticlinal walls, resulted in the most effective treatments. The results indicated that temperature at application is important to adjuvant efficacy, partly because of the effect on spray deposit characteristics.

Experiments were conducted in the greenhouse to determine the effects of adjuvant and herbicide concentrations on imazamox, imazethapyr, nicosulfuron, and ICIA 0604 phytotoxicity, independent of spray retention. Equal amounts of herbicide were applied to oat in a single 0.5-μl drop or four 0.5-μl drops. Changes in adjuvant concentration influenced herbicide phytotoxicity more with application in one concentrated drop rather than in four dilute drops. Overall, herbicide phytotoxicity was greater when low adjuvant concentrations were applied in four dilute drops compared with a single concentrated drop. But when the same total amount of adjuvant was applied in one or four drops, herbicide phytotoxicity in a single drop was generally equal to or greater than in four drops. These results suggest that high herbicide phytotoxicity with high herbicide and adjuvant concentrations in low spray volumes in the field was primarily because of increased herbicide absorption rather than spray retention.

Field experiments were conducted in 1999 and 2000 to evaluate reduced-rate split-applied treatments of imazamethabenz and ICIA 0604 for wild oat control in hard red spring wheat. Single herbicide treatments were applied at standard timing to wild oat at the two- to four-leaf stage. The first split-applied treatments were made when most of the wild oat had emerged but prior to the two-leaf stage. The second split-applied treatments were made after the surviving wild oat had visibly recovered and prior to the two-leaf stage of late-emerging wild oat. Split applications of imazamethabenz or ICIA 0604 allowed the herbicide rate to be reduced by half while maintaining or improving wild oat control. Both imazamethabenz and ICIA 0604 were most effective with methylated vegetable oil adjuvants. Wheat yield and net returns were greatest for half-rate split applications of imazamethabenz and ICIA 0604 in both years, likely because of less early-season wild oat competition and reduced wheat injury caused by ICIA 0604.

Herbicide efficacy, coverage, and retention were evaluated for spray applied through Drift Guard, Turbo TeeJet, AI TeeJet, and TurboDrop drift-reducing nozzles compared to a conventional flat-fan nozzle. Percentage spray coverage detected on water-sensitive cards was greater for conventional and Drift Guard nozzles than for Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. Spray without adjuvants was retained better by redroot pigweed for treatments applied with conventional and Drift Guard nozzles than Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. However, spray with adjuvants was retained similarly for all nozzle types when averaged over spray adjuvant and two weed species. The efficiency of spray retention was greater for spray applied in 47 than in 190 L/ha spray volume for all nozzles. Paraquat and glyphosate, representing contact and translocated herbicides, respectively, provided similar grass species control for all nozzle types, regardless of spray volume. Paraquat and glyphosate were also equally or more effective in 47 compared to 190 L/ha spray volume.