Salt and Temperature Effects on Sethoxydim Spray Deposit and Efficacy

Abstract

Certain salts in the spray carrier can antagonize sethoxydim, while other salts overcome the antagonism or increase the herbicide's efficacy. Sethoxydim responses to salts have not been consistent, and the inconsistency is not completely understood. Experiments were conducted in the greenhouse to determine sethoxydim phytotoxicity to oat as influenced by salts in the spray carrier and by air temperature at and immediately after application as they alter the spray deposit characteristics. Thick amorphous spray deposits were related to ineffective sethoxydim-petroleum oil adjuvant treatments applied alone at 10 C or with bentazon at 10 or 25 C. Also, thin deposits with salt residues were related to ineffective sethoxydim treatments, as when sodium bicarbonate was present. Ammonium sulfate reduced or overcame antagonism of sethoxydim phytotoxicity caused by low temperature, bentazon, and sodium bicarbonate and gave thin deposits having close contact with the leaf epicuticular surface but without obvious salt deposits. UV light antagonism of sethoxydim phytotoxicity was different depending on temperature at and shortly after application and depending on salts in the spray mixture. The results indicate that salts in a bentazon spray carrier are in part antagonistic because of their effect on final spray deposit.