Golf Course Management

FEB 2016

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100 GOLF COURSE MANAGEMENT 02.16 A nontreated check was included. The resistant biotype of annual sedge was not controlled by halosulfuron, imazapic, sulfosulfuron, or tri - foxysulfuron (Figure 1). Conversely, these her- bicides reduced biomass for the susceptible bio- type by 62% to 80%. Glufosinate, glyphosate and MSMA reduced biomass 77% to 97% for both biotypes, while sulfentrazone reduced bio - mass of both biotypes by ~50% relative to the nontreated control. Mesotrione caused initial visual injury on both biotypes (not shown), but biomass was only reduced 17% at eight weeks after treatment. Target-site inhibition differences in the re - sistant biotype were compared with the sus- ceptible biotype of annual sedge. The halosul- furon concentration required to inhibit ALS enzymes 50% (I 50 ) was more than 172 times greater in the resistant biotype than in the sus - ceptible biotype. The DNA was also sequenced programs with ALS inhibitors because of im- proved effcacy, turfgrass safety and the fewer applications required for controlling sedges. However, bentazon should be used alone or in tank mixtures with ALS inhibitors for man - aging herbicide resistance in annual sedge populations. These alternative mechanisms of action will be important for controlling ALS- resistant biotypes in turfgrass. Recommendations This is the frst report of resistance to ALS inhibitors in annual sedge, and the frst re - port of a herbicide-resistant sedge species from a turfgrass system. The repeated use of ALS inhibitors may select for resistant biotypes of annual sedge in turfgrass. This possibil - ity demonstrates the importance of rotating mechanisms of action. As new weed species are confrmed with resistance in turfgrass, su - perintendents should be educated about the importance of herbicide rotation for sustain - able management. Acknowledgments Data presented in this article was originally published in the journal Weed Science: Patrick E. McCullough, Jialin Yu, J. Scott McElroy, S. Chen, H. Zhang, Timothy L. Grey and Mark A. Czarnota. 2016. ALS-resistant an - nual sedge confrmed in turfgrass. Weed Sci- ence 64:33-41. Literature cited 1. Heap, I. 2015. The International Survey of Herbicide- Resistant Weeds. ( Accessed May 5, 2015. 2. Shaner, D.L. 1999. Resistance to acetolactate syn - thase (ALS) inhibitors in the United States: history, occurrence, detection, and management. Journal of Weed Science Technology 44:405-411. 3. Tranel, P.J., and T.R. Wright. 2002. Resistance of weeds to ALS-inhibiting herbicides: What have we learned? Weed Science 50:700-712. Patrick McCullough ( is an associate professor and Jialin Yu is a postdoctoral research associ - ate in the Department of Crop and Soil Sciences at the University of Georgia, Griffn, Ga. Scott McElroy, Ph.D., is a professor in the Department of Crop, Soil and Environmen - tal Sciences at Auburn University, Auburn, Ala. The RESEARCH SAYS • This is the first report of resistance to ALS inhibitors in annual sedge, and the first report of a herbicide-resistant sedge species from a turfgrass system. • Repeated use of ALS inhibitors may select for resistant biotypes of annual sedge in turfgrass. • Glufosinate, glyphosate, sulfentrazone and MSMA all controlled biotypes that were resistant to ALS inhibitors. • Superintendents should be educated about the importance of herbicide rotation for sustainable management. for the gene that encodes for the target-site en- zyme (ALS). We identifed a mutation in the resistant population that was caused by the substitution of a Ser amino acid for a Pro-197 amino acid. This mutation confers resistance to ALS inhibitors in the annual sedge biotype through a target-site alteration. Preventing resistance development in sedge populations The repeated use of halosulfuron or other ALS inhibitors will exacerbate the spread of resistant sedges. Superintendents need to de - velop integrated weed management programs that prevent the establishment and spread of ALS-resistant biotypes. Applications of pre- emergence herbicides in turfgrass will be critical for managing ALS-resistant annual sedge, especially for turfgrass species suscep - tible to injury from other post-emergence herbicides. Dinitroaniline herbicides used for pre-emergence control of annual grassy weeds in turfgrass generally have limited ef - fcacy on sedges. Superintendents may need to incorporate dimethenamid (Tower, BASF), oxadiazon (Ronstar, Bayer), sulfentrazone (Dismiss, FMC Professional Solutions) or S- metolachlor (Pennant Magnum, Syngenta) in pre-emergence control programs to effectively manage annual sedge populations. These her - bicides may have signifcant limitations for use, such as cost, turfgrass injury and restric - tions on labeled areas. Selecting the appropri- ate pre-emergence herbicide may be critical for controlling annual sedge and minimizing the spread of resistant biotypes. Sulfentrazone was less effective than MSMA, glufosinate and glyphosate for con - trolling ALS-resistant annual sedge in green- house experiments. However, feld experi- ments conducted in the summer of 2015 on ALS-resistant annual sedge revealed good (80% to 89%) to excellent (90% to 100%) control from single applications of Dismiss at 12 ounces/acre (420 grams ai/hectare). Sulfentrazone has residual activity and may be applied for pre- or post-emergence control of annual sedge. The potential loss of organic arsenical herbicides, including MSMA, could limit the mechanisms of action available to su - perintendents and further increase the occur- rence of ALS-resistant sedges. Bentazon (Ba- sagran, BASF) is a Photosystem II inhibitor that offers turf managers an alternative to ALS inhibitors for annual sedge control. Many su - perintendents have replaced bentazon in spray ALS-resistant annual sedge populations fourish in the feld.

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