Glasshouse and growth chamber experiments were conducted to determine chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} phytotoxicity to kochia [Kochia scoparia(L.) Schrad. ♯ KCHSC] and green foxtail [Setaria viridis(L.) Beauv. ♯ SETVI] as influenced by temperature and humidity for 1 week after treatment, and by soil moisture and nitrogen. Chlorsulfuron was more phytotoxic to both kochia and green foxtail at 95 to 100% than at 45 to 50% relative humidity for 1 week after treatment whether at 10, 20, or 30 C. Chlorsulfuron phytotoxicity was similar with all posttreatment temperatures at each humidity, except that phytotoxicity was lower at 30 C than at 10 or 20 C at 90 to 100% humidity. Surfactant added to chlorsulfuron exhanced control of kochia more than that of green foxtail and overcame temperature and humidity effects on chlorsulfuron phytotoxicity. A simulated rainfall of 2 mm after chlorsulfuron application reduced toxicity of chlorsulfuron to green foxtail more than to kochia. Chlorsulfuron was more phytotoxic to green foxtail growing with a high than a low soil nitrogen level. High soil moisture following chlorsulfuron application enhanced phytotoxicity to kochia and green foxtail compared to high soil moisture before treatment.

2,4-D diethanolamine control of kochia was influenced by the source of water used as the spray carrier. Sodium bicarbonate in one water source related to the reduced kochia control. Sodium bicarbonate in a water spray carrier antagonized 2,4-D control of all plant species evaluated. Antagonism increased with the tolerance of a species to 2,4-D, concentration of sodium bicarbonate, and spray volume. Sodium bicarbonate antagonism of 2,4-D phytotoxicity was greatest with low temperature and relative humidity.

Research was conducted to determine the influence of salts on 2,4-D toxicity to kochia. Calcium, magnesium, sodium, potassium, and iron salts except for sulfate and phosphate salts of calcium and sodium were antagonistic to 2,4-D diethanolamine. None of the ammonium salts antagonized 2,4-D control of kochia. Effects of individual ions generally antagonistic to 2,4-D were additive when in mixture. 2,4-D generally controlled kochia better when mixed with various acids than with their ammonium salts in distilled, sodium bicarbonate, or ferric sulfate water carriers, relating to the lower pH with the acids. However, low pH was not essential in overcoming salt antagonism of 2,4-D for kochia control, nor was 2,4-D always effective with low pH. Sulfate and monobasic phosphate anions were most effective in overcoming sodium bicarbonate and calcium chloride antagonism of 2,4-D. The concentration of diammonium sulfate needed to overcome sodium bicarbonate antagonism of 2,4-D increased with sodium bicarbonate concentration. Diammonium sulfate at 2% (w/v) overcame 1200 mg L–1sodium as sodium bicarbonate. Nonionic surfactants and oil adjuvants also overcame antagonism of 2,4-D caused by water from several sources.

Adjuvants enhanced DPX-V9360 control of green foxtail in the greenhouse and field as follows: methylated sunflower oil > petroleum oil > nonionic surfactant WK > nonionic surfactant X-77. DPX-V9360 applied at rates that controlled weeds did not injure corn. Green foxtail control with DPX-V9360 decreased as the amount of simulated rainfall after application increased from 0 to 4 mm and control increased as a 2 mm simulated rainfall was delayed up to 24 h. The influence of simulated rainfall differed with adjuvants, but adjuvants did not overcome the lower green foxtail control with simulated rainfall. DPX-V9360 was more phytotoxic to green foxtail and redroot pigweed at 95 to 100% than 45 to 50% relative humidity and at 20 or 30 C than 10 C after treatment.

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.