Effect of Temperature on Phytotoxicity and Root Uptake of Several Herbicides

The phytotoxicity of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) to corn ( Zea mays L.) and soybean ( Glycine max (L.) Merr.) seedlings and 2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine (atrazine) to soybean seedlings increased with increasing temperature from 20 to 30 C. The phytotoxicity of α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine (trifluralin) did not change significantly between 20 and 30 C. Corn and soybean plants grown at 30 C translocated more 14 C from 14 C-atrazine and soybeans more 14 C from 14 C-linuron to the shoots during the 4-hr root uptake treatment period than plants grown at 20 C. There was less accumulation of 14 C from 14 C-atrazine in soybean roots and 14 C-linuron and 14 C-trifluralin in the roots of corn and soybean plants grown at 30 C compared to those grown at 20 C. Comparison of data at 30 C and 20 C during the 4-hr root uptake treatment period showed enhanced root to shoot movement of 14 C from 14 C-atrazine in corn and from 14 C-linuron in soybean at the higher uptake treatment temperature indicating a possible relationship between increased herbicide transport to the shoot at high temperature and increased phytotoxicity.