Golf Course Management

FEB 2016

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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98 GOLF COURSE MANAGEMENT 02.16 Annual sedge resistance to halosulfuron and other ALS inhibitors in turfgrass Confrmation of resistant sedges adds to the growing problem of herbicide-resistant weeds in turf. Patrick McCullough, Ph.D. Jialin Yu, Ph.D. Scott McElroy, Ph.D. The introduction of halosulfuron to the turf industry in the 1990s provided a highly ef - fcacious post-emergence herbicide for control- ling annual and perennial sedge species. This herbicide provided more consistent control than bentazon (Basagran, BASF) and offered better selectivity than MSMA (monosodium acid methanearsonate). Halosulfuron is an ac - etolactate synthase (ALS) inhibitor with low use rates and limited injury potential to toler - ant turfgrasses. Other ALS inhibitors intro- duced more recently for sedge control in turf- grass are fazasulfuron (Katana, PBI-Gordon), sulfosulfuron (Certainty, Monsanto) and tri - foxysulfuron (Monument, Syngenta). These herbicides are highly effcacious for sedge con - trol but are injurious to cool-season grasses. Halosulfuron is the only ALS inhibitor labeled for sedge control in all major warm- and cool- season turfgrasses. Resistance to ALS inhibitors Resistance to ALS inhibitors has increased exponentially during the past decade in various cropping systems. Resistance in weeds to these herbicides is attributed to either target-site al - teration or enhanced herbicide degradation (3). Of the two, target-site alteration occurs more frequently and results in greater levels of ALS resistance (2). There are currently fve sedge species with ALS resistance reported, includ - ing shortleaf spike sedge [Cyperus brevifolius (Rottb.) Endl. Ex Hassk], smallfower um - brella sedge (C. difformis L.), yellow nutsedge (C. esculentus L.), rice fatsedge (C. iria L.) and fragrant fatsedge (C. odoratus L.) (1). Fragrant fatsedge, rice fatsedge and smallfower um - brella sedge are annuals that reproduce from seed, while the others are perennials that repro - duce from seed and tubers. An annual sedge (C. compressus L.) biotype with suspected resistance to ALS inhibitors was identifed in a bermudagrass turf in Geor - gia. The turfgrass manager noted reductions in annual sedge control after using halosulfuron exclusively for more than a decade. Research was conducted to evaluate (1) the level of re - sistance of this biotype to halosulfuron, (2) ef- fcacy of various herbicides for control, and (3) molecular and physiological mechanisms asso - ciated with resistance. Evaluation of annual sedge resistance to halosulfuron and other herbicides Green ouse experiment 1 Annual sedge plants were collected from a Tifway bermudagrass feld in Georgia on Sedges are troublesome weeds, and several species have been reported to be resistant to the herbicides known as ALS inhibitors. This paper is the frst report of a sedge in turfgrass that has shown resistance to ALS inhibitors. Photos by Patrick McCullough

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