Effect of Sunlight on the Phytotoxicity of Some Phenylurea and Triazine Herbicides on a Soil Surface

Abstract

Toxicity to oats of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), monuron (3-(p-chlorophenyl)-1,1-dimethylurea), and fenuron (3-phenyl-1,1-dimethylurea), exposed to sunlight on soil surface for 25 days was significantly decreased even when surface soil temperatures did not exceed 120 F. Only atrazine and monuron exhibited significantly less phytotoxicity after 60 days exposure than after 25 days. Simazine phytotoxicity also was significantly reduced when held on soil in the dark for 60 days. With the exception of fenuron, there was no difference between treatments within compounds when soil temperatures reached maximums as high as 180 F. Under these conditions, phytotoxicity of the herbicides was reduced 65 to 97 percent by all exposures.