Effect of Temperature and Relative Humidity on Translocation of¹⁴C-Metriflufen in Johnsongrass (Sorghum halepense) and Soybean (Glycine max)

Absorption and translocation of 14 C-metriflufen {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} in johnsongrass [ Sorghum halepense (L.) Pers.] and soybean [ Glycine max (L.) Merr. ‘Lee 68’] were evaluated under different environmental conditions. At 40% relative humidity (RH), an increase in air temperature from 18 to 35 C increased translocation of the 14 C in johnsongrass more than four-fold following application of 14 C-metriflufen to an area on the third leaf. At 100% RH, translocation of the 14 C was twice as great at 27 C as at 18 C, but translocation at 35 C was intermediate. In the combined analysis, translocation in johnsongrass was no better at 100% RH than at 40% RH. Regardless of level of RH, most translocation in johnsongrass at 18 and 27 C was toward the distal half of the treated leaf, but at 35 C most translocation was toward the proximal half of the treated leaf. Translocation of 14 C in soybeans increased more than four-fold as air temperature was increased from 18 C to 35 C, and more translocation occurred at 100% RH than at 40% RH at 18, 27, and 35 C. More than 80% of the 14 C-metriflufen remained in the treated leaf or on the surface of treated soybean leaves 48 h after application. More of the applied radioactivity was recovered from soybean plants than from johnsongrass plants.