Abstract: Nicosulfuron efficacy varies with surfactant, natural salts in the spray water carrier, and added nitrogen fertilizer salts. Scanning electron micrographs (SEM) were taken of nicosulfuron spray droplet residue on large crabgrass in the greenhouse. Spray residue characteristics differ for nicosulfuron applied with surfactants alone and with specific salts. Uniform deposits with close contact to the leaf epicuticular surface generally related positively to nicosulfuron efficacy. Ammonium salt enhancement of nicosulfuron phytotoxicity when with surfactant X-77® related to a change from a ring to a uniform deposit. Spray mixtures containing Tween 20 or Atplus 300F surfactants that gave distinct dark amorphous deposits over anticlinal cell walls generally related to effective nicosulfuron treatments. Salts that were antagonistic to nicosulfuron phytotoxicity left a large amorphous deposit, including ammonium nitrate antagonism of nicosulfuron applied with Pluronic® P85 surfactant and general antagonism from sodium bicarbonate. The SEM information indicates that the effect of surfactants and salts on spray deposit characteristics influence nicosulfuron efficacy.

Nomenclature: Nicosulfuron, 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; large crabgrass, Digitaria sanguinalis (L.) Scop.

Additional index words: Adjuvant, antagonism, ammonium nitrate, urea, sodium bicarbonate, spray technology.

Abbreviations: SEM, scanning electron micrographs; 28% N, liquid fertilizer containing ammonium nitrate and urea.