Influence of Temperature and Relative Humidity on the Activity of Acifluorfen

The influence of temperature and relative humidity on the activity of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} on common cocklebur ( Xanthium pensylvanicum Wallr.) and common ragweed ( Ambrosia artemisiifolia L.) was studied in growth chambers. Treatment at high relative humidity (85 ± 5%) resulted in a significant increase in acifluorfen phytotoxicity and decrease in plant dry weight as compared to treatment at a lower (50 ± 5%) relative humidity (RH). Temperature (32 C day, 22 C night or 26 C day, 16 C night) was not as critical as relative humidity in influencing acifluorfen phytotoxicity. Addition of a non-ionic surfactant to the herbicide solution resulted in increased phytotoxicity. Penetration and translocation of acifluorfen in common cocklebur were increased when applications were made at high relative humidity.