Spray deposits from nicosulfuron with salts that affect efficacy

Nicosulfuron efficacy varies with surfactant, natural salts in the spray wa ter carrier and added nitrogen fertilizer salts. Scanning electron microgra phs (SEM) were taken of nicosulfuron spray droplet residue on large crabgra ss in the greenhouse. Spray residue characteristics differ for nicosulfuron applied with surfactants alone and with specific salts. Uniform deposits w ith close contact to the leaf epicuticular surface generally related positi vely to nicosulfuron efficacy. Ammonium salt enhancement of nicosulfuron ph ytotoxicity when with surfactant X-77(R) related to a change from a ring to a uniform deposit. Spray mixtures containing Tween 20 or Atplus 300F surfa ctants that gave distinct dark amorphous deposits over anticlinal cell wall s generally related to effective nicosulfuron treatments. Salts that were a ntagonistic to nicosulfuron phytotoxicity left a large amorphous deposit, i ncluding ammonium nitrate antagonism of nicosulfuron applied with Pluronic( R) P85 surfactant and general antagonism from sodium bicarbonate. The SEM i nformation indicates that the effect of surfactants and salts on spray depo sit characteristics influence nicosulfuron efficacy.