Hybrid bermudagrass [Cynodon dactylon (L.) Pers.] tolerance and broadleaf weed control using tank mix combinations of diflufenzopyr
Matocha, Matthew Edward
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Field studies were conducted during the 2003 and 2004 growing seasons to: 1) evaluate the control of silverleaf nightshade and western ragweed, and (2) assess the forage tolerance of Coastal and Tifton 85 bermudagrass hybrids using tank mix combinations of diflufenzopyr. Herbicides that were evaluated in each study included picloram, multiple rates of picloram with diflufenzopyr, triclopyr, triclopyr with diflufenzopyr, dicamba + diflufenzopyr, and diflufenzopyr alone. Visual ratings were taken on the weed control experiments approximately 30, 60 and 90 days after treatment. Phytotoxicity ratings were taken prior to each harvest of the Coastal and Tifton 85 varieties to determine influence of each herbicide treatment. Each bermudagrass variety was harvested twice during each growing season to determine dry matter yield and quality. Forage quality, including crude protein, acid detergent fiber, and neutral detergent fiber, was assessed using near infrared reflectance spectroscopy. Adding diflufenzopyr to triclopyr did not consistently increase control of silverleaf nightshade or western ragweed. In general, picloram + diflufenzopyr and picloram applied alone provided the greatest control of both species at the highest rate of picloram. Increased efficacy was more evident from the addition of diflufenzopyr to picloram in 2004 on western ragweed. By the final ratings in both experimental years, dicamba + diflufenzopyr provided no more than 76% control of either species. Both forage varieties showed significant variability in phytotoxicity between years. Although observed levels of growth reduction were relatively high at the first harvest in 2003, no treatment exceeded a 10% growth reduction by the second harvest for either forage variety. In addition, the only significant reduction in dry matter yield occurred at the first harvest of Coastal in 2003 from picloram + diflufenzopyr applied at the highest rate.