Field experiments were conducted to determine the influence of growth stage on tolerance of seeded tomatoes (Lycopersicon esculentum Mill.) and of eastern black nightshade (Solanum ptycanthum Dun. #3 SOLPT) to the sodium salt of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} at low use rates. Tomatoes as young as the 2 true-leaf stage exhibited some tolerance to acifluorfen at rates of 0.14 kg ae/ha and less. Rates of 0.28 and 0.56 kg/ha caused increased phytotoxicity; however, yield was not greatly reduced. At the 8-leaf stage, foliar injury was slight and existed only at the highest rates tested; however, tomato yields were reduced. Control of black nightshade at the 2-leaf stage was acceptable at rates as low as 0.14 kg/ha. When nightshade was at the 5-leaf stage, 0.28 and 0.56 kg/ha rates provided acceptable control − 87% and 96%, respectively. Nightshade in the 10-leaf stage was not controlled effectively at rates below 0.56 kg/ha.

Carryover potential of imazaquin (0.14 kg ai ha−1), chlorimuron plus metribuzin (0.06 + 0.36 kg ha−1), and fomesafen (0.28 kg ha−1) to snap bean, watermelon, cucumber, mustard, and sunflower was evaluated in Arkansas in 1987 to 1989. Crops were direct-seeded into treated plots at various times after application. Imazaquin and chlorimuron plus metribuzin injured sunflower, watermelon, cucumber, and mustard when planted 16 wk following application in one of two years. Fomesafen injured all crops initially but did not injure snap bean, sunflower, watermelon, and cucumber planted 16 wk after application. In experiments in which herbicides were applied to soybean, fall-planted spinach and mustard were injured in one of two years.

Penetration, translocation, and metabolism of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in soybean [Glycine max (L.) Merr. ‘Ransom’], common ragweed (Ambrosia artemisiifolia L.), and common cocklebur (Xanthium pensylvanicum Wallr.) were studied. Using liquid scintillation spectrometry and autoradiography, little movement of 14C-acifluorfen from the leaf surfaces of the two weed species could be detected in 24 h. After 48 h, less 14C was recovered from the leaf surface and more was found within the leaves of the two weed species. Autoradiographs of the weed showed limited acropetal movement of 14C from leaves 24 and 48 h after treatment. For soybean, most of the 14C still remained on the leaf surface after 48 h. Autoradiographs of soybean plants showed no movement from the treated leaflet. Studies using thin layer chromatography suggested that acifluorfen was metabolized within the plants. Rate of metabolism was inversely related to plant susceptibility (common ragweed and common cocklebur>soybean). The more rapid penetration and translocation, coupled with slower metabolism of acifluorfen by the weed species in comparison to soybean, may account for the difference in susceptibility of the weeds and soybean to 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.