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Title: Response of three switchgrass (Panicum Virgatum) cultivars to mesotrione, quinclorac, and pendimethalin

Author
item Boydston, Rick
item Collins, Harold
item FRANSEN, STEVE - Washington State University

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2010
Publication Date: 7/1/2010
Citation: Boydston, R.A., Collins, H.P., Fransen, S. 2010. Response of Three Switchgrass (Panicum virgatum) Cultivars to Mesotrione, Quinclorac, and Pendimethalin. Weed Technology. 24:336-341.

Interpretive Summary: Weed management is an important component of successful switchgrass stand establishment and failure to control weeds can result in poor stands and the need to replant. Annual grass weeds are often a problem do to the lack of effective herbicides available for grass control in new switchgrass plantings. Three herbicides were tested for annual grass weed control and switchgrass tolerance in 2005 and 2006 in both new planted and established switchgrass. Three switchgrass cultivars were included in each study. Pendimethalin applied to newly planted switchgrass severely injured and nearly eliminated switchgrass stands in both years. Mesotrione injured newly planted switchgrass, and reduced final switchgrass biomass by 54% both years. Kanlow cultivar was injured less by mesotrione than Cave-in-Rock and Shawnee cultivars. Quinclorac injured newly planted switchgrass the least, but reduced final switchgrass biomass by 33% both years. All three herbicide treatments controlled large crabgrass well in the year of establishment. Pendimethalin did not injure 1-year old established switchgrass or reduce switchgrass biomass. Quinclorac applied to established switchgrass reduced switchgrass biomass of the first harvest by 16% in one of two years, whereas mesotrione caused unacceptable injury to established switchgrass. Established switchgrass suppressed late emerging annual grass weeds sufficiently to not warrant a grass specific herbicide application.

Technical Abstract: Annual grass weed control and switchgrass cultivar response to preemergence (PRE) applied pendimethalin and postemergence (POST) applied mesotrione and quinclorac was evaluated in 2005 and 2006 near Paterson, WA in both newly seeded and established switchgrass. Pendimethalin applied to newly planted switchgrass at 1.1 kg/ha at the 1-leaf stage in 2005 or at 0.6 kg/ha PRE in 2006 severely injured and nearly eliminated switchgrass stands. Mesotrione applied POST at 0.07 kg/ha injured newly planted switchgrass, reduced switchgrass height for several weeks after treatment, and reduced final switchgrass biomass by 54% both years. Kanlow and Cave-in-Rock cultivars were injured less by mesotrione than Shawnee in 2005, while in 2006 Kanlow was injured less than Shawnee and Cave-in-Rock. Quinclorac applied POST at 0.56 kg/ha injured newly planted switchgrass less than mesotrione and pendimethalin, but reduced final switchgrass biomass by 33% both years compared to treatment with atrazine alone. All three herbicide treatments controlled large crabgrass well in the year of establishment. Green foxtail counts were reduced 93% or more by pendimethalin and quinclorac compared to nontreated controls, but mesotrione failed to control green foxtail. Pendimethalin applied PRE at 1.1 kg/ha did not injure 1-year old established switchgrass or reduce switchgrass biomass. Quinclorac applied POST at 0.56 kg/ha to established switchgrass reduced switchgrass biomass of the first harvest by 16% in one of two years. Mesotrione applied POST at 0.07 kg/ha injured established switchgrass and reduced biomass of the first harvest by 33 and 17% in 2005 and 2006, respectively. Kanlow cultivar was injured the least by mesotrione in both years. Established switchgrass suppressed late emerging annual grass weeds sufficiently to not warrant a grass specific herbicide application.