Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha−1), nicosulfuron (0.07 kg ai ha−1) + metsulfuron (0.012 kg ai ha−1), and hexazinone (1.3 kg ai ha−1) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha−1) or pendimethalin (4.46 kg ai ha−1) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

Research was conducted in 2003 and 2004 to evaluate diflufenzopyr tank mixes for western ragweed control and injury to ‘Tifton 85′ bermudagrass. In 2003 at 94 DAT, picloram at 0.28 and 0.56 kg ae ha−1 with or without diflufenzopyr provided greater than 95% control of western ragweed, whereas triclopyr + dilfufenzopyr, dicamba + diflufenzopyr, triclopyr alone, and diflufenzopyr alone provided < 77% control. In 2004 at 95 DAT, only the highest rate of picloram alone provided 96% control, and the two highest rates of picloram + diflufenzopyr provided at least 95% control. Tifton 85 bermudagrass growth reduction increased with the addition of diflufenzopyr to picloram in 2003, but not in 2004. However, forage dry-matter yield was not reduced by any herbicide treatment compared to the nontreated control. Results of these studies indicate that picloram alone and picloram + diflufenzopyr provide excellent control of western ragweed. The tank mixture of picloram + diflufenzopyr can improve control over picloram alone. However, dicamba + diflufenzopyr, triclopyr + diflufenzopyr, triclopyr alone, and diflufenzopyr alone did not provide adequate control.