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Chuck Ingels and John Roncoroni

Dune sedge (Carex pansa) can be used as either a groundcover or mowed turf. It is planted as plugs or small pots, but at 9-inch spacing, it may take over 1 year to completely fill in as turf, allowing weeds to grow between plants. This research was conducted to evaluate control of annual weeds and crop phytotoxicity with several conventional and reduced-risk herbicides in newly transplanted dune sedge. Three experiments were conducted on the same planting over a 5-month period, with dune sedge plants and weeds recovering well to permit subsequent evaluations. In Expt. 1, four preemergent and four reduced-risk postemergent herbicides and shredded fir bark mulch were compared shortly after planting. The use of oryzalin, dithiopyr, an experimental fatty acid herbicide (experimental FA), and mulch led to good control of the young weeds; all others resulted in less than 50% control. The experimental FA and ammoniated soap of fatty acids caused phytotoxicity to the dune sedge. In Expt. 2, four postemergent conventional herbicides, the same four reduced-risk postemergent herbicides (including two at increased rates) and the continued mulch treatment were tested. Most reduced-risk herbicides severely burned back the weeds initially, but regrowth ensued. In Expt. 3, a grass herbicide, a broadleaf herbicide combination, and a mix of the two were compared on the remaining plots with healthy dune sedge and actively growing weeds. Fluazifop provided good control of wild oat, carfentrazone + 2,4-D + mecoprop + dicamba largely controlled broadleaf weeds, and the combination controlled most weeds; no phytotoxicity occurred to the dune sedge. The results of the three experiments suggest that an application of dithiopyr, oryzalin, or a 2-inch layer of mulch shortly after planting, followed if necessary by hand weeding or treating weeds with carfentrazone + 2,4-D + mecoprop + dicamba tank-mixed with fluazifop would be an ideal strategy for management of annual weeds during the establishment of dune sedge. For organic or reduced-risk management, bark or wood chip mulch followed by hand weeding would be the best approach.