Phytotoxicity of Glyphosate to Italian Ryegrass (Lolium multiflorum) and Red Clover (Trifolium pratense)

The phytotoxicity of glyphosate [N-(phosphonomethyl) glycine] on seeds (protected or non-protected with soil) and seedlings of Italian ryegrass (Lolium multiflorum Lam.) and red clover (Trifolium pratense L.) was studied in the greenhouse. Percent germination of Italian ryegrass seeds covered with soil was significantly reduced with glyphosate applied at 4 kg/ha. The direct treatment over the seeds on the soil surface was more toxic, reducing the number of established seedlings at dosages of 3 and 4 kg/ha. In the two red clover seed treatments, germination was significantly reduced with 2 kg/ha of herbicide. Even though germination was reduced at intermediate rates of glyphosate, shoot growth and tillering were improved and yields of dry weight were equivalent to that of untreated plants. Postemergence applications of glyphosate were phytotoxic to both species with the effects becoming more pronounced at increasing dosages. However, at equal dosage, red clover was less susceptible than Italian ryegrass. The patterns of foliar absorption and translocation of 14C from 14C-glyphosate was similar in Italian ryegrass and red clover. 14C was translocated throughout the plants and exhibited apoplastic and symplastic movement.