Enhancing the Biological Activity of Nicosulfuron with pH Adjusters1

Abstract

Adjuvants that increase the pH of the spray mixture and solubilize nicosulfuron can enhance biological activity under specific conditions. These conditions include high nicosulfuron rates, difficult-to-control weeds, low spray volumes, and initially acidic spray conditions. The most effective pH adjusters are tribasic potassium phosphate, sodium carbonate, and triethanolamine. In low spray volumes, these adjusters make the spray mixture alkaline and often enhance the activity of nicosulfuron on common cocklebur and large crabgrass. Alkaline conditions rapidly dissolve the sulfonylurea particles and enhance activity with crop oil concentrate, modified seed oil, and hydrophilic nonionic surfactants. pH adjusters did not enhance activity with lipophilic surfactants. Ammonium sulfate slightly increases the pH of spray mixtures and increases nicosulfuron activity depending on species, adjuvant type, and pH adjuster. These results generally support the concept that herbicide solubilization is necessary to maximize the foliar activity.Nomenclature: Nicosulfuron; common cocklebur, Xanthium strumarium L. #3 XANST; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA.Additional index words: Adjuvant, basic blend, buffer, crop oil concentrate, fertilizer, formulation, hydrophilic–lipophilic balance, methylated seed oil, modified seed oil, nonionic surfactant, potassium phosphate, soda ash, sulfonylurea, triethanolamine, water-dispersible granule.Abbreviations: AMS, ammonium sulfate; COC, crop oil concentrate; HLB, hydrophilic–lipophilic balance; MSO, modified seed oil; NIS, nonionic surfactant; NPE, nonylphenol ethoxylate; TEA, triethanolamine; WDG, water-dispersible granule.