Choice of Adjuvant with Halosulfuron Affects Purple Nutsedge Control and Nursery Crop Tolerance

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  • 1 Department of Ornamental Horticulture and Landscape Design, University of Tennessee, Knoxville, TN 37996-4500

One-half (18 g·ha-1 a.i.) and three-fourths (27 g·ha-1 a.i.) rates of halosulfuron (Manage®, MON 12051) were combined with adjuvants and evaluated for effectiveness in controlling purple nutsedge (Cyperus rotundus L.) and for phytotoxic responses exhibited by two kinds of container-grown ornamental plants. Adjuvants included X-77®, Scoil®, Sun-It II®, Action “99”®, and Agri-Dex®. By 8 weeks after treatment (WAT), halosulfuron combined with X-77®, Agri-Dex®, or Action “99”® at the lower halosulfuron rate provided <90% purple nutsedge suppression. In contrast, Sun-It II® provided 100% control when combined with the higher halosulfuron rate. Nutsedge control persisted into the following growing season and halosulfuron combined with either Scoil® or Sun-It II® provided >97% suppression of nutsedge tuber production. Growth of liriope [Liriope muscari (Decne.) Bailey `Big Blue'] was not inhibited by Scoil® or Sun-It II® adjuvants in combination with the low rate of halosulfuron. However, regardless of the rate of halosulfuron or adjuvant used, initial foliar chlorosis was observed in both daylily (Hemerocallis sp. L. `Stella d'Oro') and liriope. All liriope receiving halosulfuron with X-77®, Scoil®, or Sun-It II® adjuvants recovered normal foliage by 8 WAT. By contrast, at 8 WAT some daylily still maintained a degree of foliar discoloration. In addition to chlorosis, all treatments reduced flower number in daylilies. The number of flower scapes produced by liriope was not affected by halosulfuron when in combination with either Sun-It II® or Scoil®. The high rate of halosulfuron combined with X-77® or Action “99”® improved control of purple nutsedge. However, this rate inhibited growth of both species, daylily flower numbers, and scape numbers of liriope, regardless of adjuvant. Chemical names used: halosulfuron (Manage®, MON 12051, methyl 5-{[(4,6-dimethyl-2-pyrimidinyl) amino] carbonyl-aminosulfonyl}-3-chloro-1-methyl-1-H-pyrozole-4-carboxylate); proprietary blends of 100% methylated seed oil (Scoil® and Sun-It II®); proprietary blend of 99% polyalkyleneoxide modified heptamethyl trisiloxane and nonionic surfactants (Action “99”®); alkylarylpolyoxyethylene, alkylpolyoxyethelene, fatty acids, glycols, dimethylpolysiloxane, and isopropanol (X-77®); proprietary blend of 83% paraffin-based petroleum oil, with 17% polyoxyethylate polyol fatty acid ester and polyol fatty ester as nonionic surfactants (Agri-Dex®)

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