Abstract: Four species of grassy weeds, Digitaria sanguinalis, Eleusine indica, Setaria viridis, and Chloris virgata, are the main grassy weeds in the northern maize region and Huang-Huai-Hai maize region in our country affecting maize yield and quality. In our study, the whole plant bioassay was used to determine the sensitivity baseline of these four species of weeds to glyphosate, which may provide support for future weed control in fields planted with transgenic glyphosate-tolerant maize in China. The results showed that GR₅₀ values of 55 populations of D. sanguinalis ranged from 13.36 to 550.28 g a.i./ha, with an average of 120.02 g a.i./ha. The GR₅₀ values of 69 populations of S. viridis ranged from 7.22 to 201.96 g a.i./ha, with an average of 50.45 g a.i./ha. The range of GR₅₀values in 50 populations of E. indica was 25.19―808.54 g a.i./ha, with an average of 218.78 g a.i./ha. All the GR₅₀ values of D. sanguinalis, E. indica, and S. viridis were below 900 g a.i./ha (the recommended medium dose in the field), indicating that these 3 weed species were sensitive to glyphosate. The GR₅₀ values of 34 populations of C. virgata ranged from 37.79―1309.21 g a.i./ha, with an average of 358.33 g a.i./ha. There was only one population of C. virgata with GR₅₀ value over 900 g a.i./ha, indicating that 97% of C. virgata populations were sensitive to glyphosate and only a few population were tolerant to glyphosate.

Key words: glyphosate, grassy weeds, sensitivity