Experiments were conducted in the greenhouse to determine nicosulfuron activity on large crabgrass as influenced by surfactant, ammonium salt adjuvants, and various calcium, sodium, and magnesium salts in the spray carrier. Nicosulfuron activity varied with surfactant. Ammonium salt adjuvants at 0.2 M (ammonia) and sodium, calcium, or magnesium salts at 0.02 M (cation) increased or decreased nicosulfuron activity dependent on the specific salt and surfactant. Spray carrier surface tension or pH of the spray solution did not relate to nicosulfuron activity. The specific ammonium component influenced nicosulfuron activity differently depending on the surfactant. Increases in ammonium nitrate concentration decreased, nicosulfuron activity with Pluronic® P85 surfactant and increased activity with X-77® surfactant. The response to ammonium nitrate was less pronounced at high surfactant concentrations. Sodium bicarbonate antagonism of nicosulfuron activity was overcome by ammonium sulfate and 28% aqueous nitrogen fertilizer in the presence of several oil and surfactant adjuvants. The results indicate the importance of surfactant selection for use with nicosulfuron when applied with nitrogen salts.

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.

Spray carrier pH affects the solubility of sulfonylurea herbicides and, therefore, could affect absorption and subsequent translocation of these compounds in weeds. Trifloxysulfuron is a sulfonylurea herbicide developed for POST weed control in cotton, sugarcane, and turfgrass with a pKa of 4.81. The objective of this study was to evaluate the absorption and translocation of foliar-applied 14C-trifloxysulfuron in Palmer amaranth and Texasweed at pH 5, 7, and 9 over a period of 4 to 72 h after treatment (HAT). For absorption, effects of time, species, and pH were significant. Absorption averaged over species and pH increased logarithmically from 4 to 72 HAT. Absorption was greater for Palmer amaranth (88%) than for Texasweed (29%) when averaged over time and pH. Absorption averaged over species and time increased in the order of pH 5 (52%) < pH 9 (60%) = pH 7 (61%). Consequently, this translated into greater translocation of 14C-trifloxysulfuron in Texasweed when sprayed with the higher pH spray solutions. These data indicate that absorption and translocation of trifloxysulfuron in some weed species may be enhanced by increasing the pH of the spray solution by 2 pH units above the pKa.