Effect of Environment on the Translocation and Toxicity of Acifluorfen to Showy Crotalaria (Crotalaria spectabilis)

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Abstract
Toxicity of non-radiolabeled and absorption and translocation of 14C-activity of applied 14C-acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in showy crotalaria (Crotalaria spectabilis Roth) were evaluated in the growth chamber at air temperatures of 18, 27, or 35 C and 40 or 100% relative humidity (RH). Four days after treatment, acifluorfen applied over-the-top at 0.1 kg/ha resulted in 64 to 95% injury, but did not kill showy crotalaria. Acifluorfen was more toxic at 100% than at 40% RH. At either 40 or 100% RH, acifluorfen was more toxic at 27 and 35 C than at 18 C. Plants were placed in the greenhouse 4 days after treatment. At 6 weeks after treatment, there was extensive regrowth, and injury to all plants was less than 32%, except for those plants initially treated at 18 C and 40% RH for 4 days. These plants showed 76% injury. Acifluorfen applied to a single leaf midway up the stem caused 80 to 100% injury to the immature leaves near the apex, but less than 30% injury to lower leaves. Absorption of 14C-activity from 14C-acifluorfen applied to a single leaf midway up the shoot varied from 8 to 76% after 2 days. At either 40 or 100% RH, absorption was approximately four-fold greater at 27 and 35 C than at 18 C. At all temperatures tested, absorption was three- to four-fold greater at 100% than at 40% RH.