Dates of Glyphosate Treatments on Weeds and Bermudagrass(Cynodon dactylon)

Glyphosate [N-(phosphonomethyl)glycine] consistently controls many winter annual weeds in dormant bermudagrass [Cynodon dactylon(L.) Pers.] but injures actively growing turf. Experiments were conducted to determine the effects of dates of glyphosate treatments on control of winter annuals in different stages of maturity and on the tolerance of bermudagrass when applied to the turf at different stages of greenness from dormant turf in the winter to actively growing turf in the spring. Glyphosate was applied at rates of 0, 0.3, 0.6, 1.1, and 2.2 kg/ha to different plots of winter annuals and bermudagrass at 3-week intervals from February 13 to May 3. Glyphosate at 0.3 kg/ha controlled at least 90% of annual bluegrass(Poa annuaL.), spur weed(Soliva sessilisP. & K.), and corn speedwell(Veronica arvensisL.) within a 6-week period regardless of the date of treatment. All glyphosate treatments injured bermudagrass when applied to semi-dormant or actively growing turf. Bermudagrass treated with glyphosate at 0.3 kg/ha was injured the least and the turf had essentially recovered by 6 weeks after treatment. However, the injury from higher rates (0.6 to 2.2 kg/ha) was too severe to be acceptable in turf areas. Glyphosate did not severely injure bermudagrass when applied to dormant turf.