Use of Selected Herbicides and Application Methods for Tolerance to Tifton 85 Bermudagrass [Cynodon dactylon (L.) Pers.]

Abstract

Aims: To evaluate forage tolerance of Tifton 85 bermudagrass to selected pasture herbicides using two application methods: broadcast (BRD) and individual plant treatments (IPT). Study Design: A randomized complete block design was employed with four replications. Place and Duration of Study: Trials were conducted during the 2006 and 2007 growing seasons near Thrall, Texas, (30.35o N, 97.17o W). Methodology: Two spray application methods (BRD and IPT) were compared when using selected herbicides for bermudagrass tolerance. Herbicides evaluated by BRD included picloram plus fluroxypyr, picloram plus fluroxypyr plus metsulfuron-methyl, triclopyr, triclopyr plus fluroxypyr, triclopyr plus metsulfuron-methyl, triclopyr plus fluroxypyr plus metsulfuron-methyl, and metsulfuron-methyl plus dicamba plus 2,4-D. Herbicides evaluated by IPT included triclopyr, triclopyr plus fluroxypyr, and picloram plus fluroxypyr. Bermudagrass injury, yield, and crude protein content were evaluated for application method and herbicide. Results: Rainfall after herbicide application in 2006 was 67% below normal while in 2007 rainfall was 350% above normal. No bermudagrass necrosis or growth reduction were noted in 2006. Triclopyr plus fluroxypyr applied IPT was the only treatment to decrease Tifton 85 dry matter yield at the first harvest, with no effect observed at the second. In 2007, necrosis was greatest with triclopyr plus fluroxypyr applied BRD while triclopyr plus fluroxypyr and triclopyr plus fluroxypyr plus metsulfuron-methyl applied BRD and triclopyr applied IPT caused the greatest growth reduction. Triclopyr and triclopyr plus fluroxypyr applied BRD or IPT and triclopyr plus fluroxypyr plus metsulfuron-methyl applied BRD decreased dry matter yield at the first harvest while only triclopyr alone applied IPT reduced yield at the second. Conclusions: The recurring bermudagrass stunting and yield reduction with triclopyr is consistent with previous forage tolerance research. Metsulfuron methyl plus dicamba plus 2,4-D was the only treatment that exhibited little or no injury, growth reduction, or yield reduction at any time. Producers need to be aware of potential injury issues with triclopyr.