EFFECT OF GLYPHOSATE ON INTRODUCED AND NATIVE GRASSES

The effect of glyphosate applied alone and with 2,4-D as a commercial mixture on 30 native or introduced grass species was evaluated. Grass yield averaged 98 and 87% of the untreated controls when glyphosate was applied in the fall at 0.2 or 0.4 kg ae ha-1, respectively, alone or with 2,4-D at 0.35 or 0.7 kg ae ha-1. Western wheatgrass production decreased more than any other species present in a native rangeland site following either a spring or fall glyphosate application. In seeded plots, intermediate wheatgrass was the most and 'Fairway' crested wheatgrass the least susceptible to glyphosate plus 2,4-D with average yields of 57 and 97% compared with untreated controls of each species, respectively. Glyphosate reduced the yield of 'Nordan' standard crested wheatgrass more than that of Fairway crested wheatgrass or other diploid cultivars. The greater the spring precipitation following a fall application of glyphosate, the less effect of glyphosate on forage yield. Glyphosate plus 2,4-D can be used for weed control in pasture and rangeland provided some yield reduction is acceptable.