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.

A nonionic surfactant with the appropriate structure and concentration increased rimsulfuron activity 10-fold. Surfactants sharply increased rimsulfuron activity as concentration increased up to 0.05% (w/w) with slightly more enhancement up to 0.1% (w/w). Surfactants with a wide range of 14 chemical, physical, and surface properties were evaluated on giant foxtail, velvetleaf, and corn. Two properties, HLB (hydrophilic-lipophilic balance) and the physical form of the spray deposit, explained the biological variation. The most active surfactants had an HLB from 12 to 17 and formed a moist gel spray deposit on the leaf on all three species. A separate study with 13 chemically pure linear alcohol ethoxylates supported these conclusions and additionally showed that increasing molecular size increases activity. Because crop injury correlates with weed control, the best surfactant strategy is to maximize weed control at the lowest rimsulfuron rate.

Field experiments were conducted to examine the influence of spray volume on glyphosate efficacy in relation to glyphosate rate, formulation, ammonium sulfate addition, and type of sprayer nozzle. Using several grass species it was shown that glyphosate efficacy increased as spray volume decreased from 190 to 23 L/ha. To obtain equal efficacy, glyphosate rates can be reduced by at least one-third when glyphosate is applied in 23 or 47 L/ha spray volume compared with 94 or 190 L/ha. The amount of surfactant in formulated glyphosate at 35 to 140 g ae/ha rates was insufficient when glyphosate was applied in 94 or 190 L/ha spray volumes. Additional surfactant enhanced glyphosate efficacy at these rates when applied in 94 or 190 L/ha spray volume, but efficacy was still less than when applied in 23 or 47 L/ha without additional surfactant. Thus, low spray volumes maximized glyphosate efficacy primarily through high herbicide concentration in the spray deposit and reduced salts from the carrier to antagonize efficacy. Glyphosate applied in 23 L/ha spray volume with drift-reducing nozzles provided control equal to that provided by glyphosate applied with standard flat-fan nozzles. Grass control also was equal from several glyphosate formulations that contained surfactants, regardless of spray volume.

Laboratory and greenhouse experiments were conducted to determine quinclorac efficacy as influenced by surfactants, methylated seed oil (MSO), basic pH compounds, and salts in the spray carrier water. Quinclorac efficacy for green foxtail control generally increased with an increase in linear alcohol ethoxylate (LAE) surfactant carbon-chain length and percentage of ethoxylation. With LAE surfactants, quinclorac phytotoxicity to green foxtail was nearly doubled (average from 44 to 81%) when triethanolamine (TEA) was included in the spray mixture. Combination of LAE surfactants with TEA also enhanced quinclorac absorption. Enhancement of quinclorac absorption and phytotoxicity by LAE surfactants and TEA was related to spray deposits that had close contact with the cuticle and without apparent quinclorac crystals. Sodium and calcium ions strongly antagonized quinclorac efficacy when applied with a block copolymer surfactant or MSO. Ammonium sulfate or ammonium nitrate adjuvants were more effective than urea–ammonium nitrate liquid fertilizer in overcoming antagonism from salts in spray carrier waters. These results demonstrate the potential for maximizing quinclorac efficacy by careful selection of surfactants, nitrogen fertilizer, and basic pH additives.