T he renewable fuel standard developed by the USEPA mandates volume requirements for renewable fuels, which will continue to increase through 2022 (USEPA, 2011). Currently, corn (Zea mays L.) is the primary feedstock for ethanol production; however, increasing human population and food demands will reduce corn available for ethanol production in the future. There is a need for alternative ethanol feedstocks from nonfood plant sources that are less competitive with human food production. Biomass is an alternative to food-plant sources and switchgrass is a viable biomass source for cellulosic ethanol production (McLaugh

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S witchgrass (Panicum virgatum L.) is a small-seeded warm-season perennial forage and potential biomass feedstock that is slow to establish (Aiken and Springer, 1995), which results in an increase of grass weeds that compete with switchgrass for nutrients and sunlight during establishment (Masters et al., 2004;Boydston et al., 2010;Mitchell et al., 2010). Controlling weeds during the establishment year can greatly improve establishment and increase biomass production in subsequent years (Schmer et al., 2006;Mitchell et al., 2010). Warm-season annual grass weeds have been shown to be detrimental to switchgrass establishment, unlike broadleaf weeds, which can easily be controlled with 2,4-d amine (2,4-dichlorophenoxyacetic acid) when switchgrass reaches the 4-leaf stage (Vogel, 2004;Anonymous, 2008b). Use of a preemergence herbicide is recommended to reduce grass weed competition while establishing warm-season perennial grasses. Application of metolachlor and/or atrazine was reported to improve biomass yield in big bluestem (Andropogon gerardii Vittman) during the second year (Masters, 1997). Little information is available documenting the effect of preemergence herbicides on the establishment of switchgrass and its control on grassy weeds. Further, it is unclear whether or not the application of a postemergence herbicide could ensure or sustain weed control while allowing successful establishment and continued switchgrass growth. Experimental design was a split-split-plot design with presence/ absence of preemergence herbicide cloransulam as main plot, weed species as subplot treatment, and postemergence herbicides as sub-subplot treatments. Herbicides foramsulfuron + pendimethalin + quinclorac was applied at the 1-to 2-and 2-to 3-leaf stage, whereas nicosulfuron was applied at 2-to 3-leaf stage and nicosulfuron combinations and MSMA were applied at 3-to 4-leaf stage. Using cloransulam as a preemergence herbicide resulted in lower switchgrass seedling numbers and generally did not improve establishment. Interseeding Johnsongrass allowed for the greatest number of switchgrass seedlings and was the least competitive weed, whereas interseeding large crabgrass resulted in the least amount of switchgrass and proved to be the most competitive weed. Foramsulfuron + pendimethalin + quinclorac resulted in effective weed control (>70%) for all four species evaluated and improved switchgrass establishment (13-26%) compared to the untreated control (0-3%); however, greater improvement in stand establishment is needed. Effect of Various Herbicides on

Switchgrass (Panicum virgatum L.) is typically slow and difficult to establish due to competition from weeds. Two experiments were conducted evaluating effectiveness of seed safeners and activated charcoal on prevention of herbicide injury of ‘Alamo’ switchgrass. In experiment I, a completely randomized greenhouse experiment with three replications evaluated a factorial arrangement of five (0, 0.64, 0.96, 1.28, and 1.92 fluid oz/100 lb seed) fluxofenin (Concep III) rates and four herbicide treatments: metolachlor, metolachlor plus atrazine, pendamethalin, and an untreated control. In experiment II, a randomized complete block field experiment with a split plot arrangement of treatments and four replications evaluated charcoal seed treatments. Main plot treatments consisted of uncoated seed plus 250 lb/acre charcoal slurry in a 2‐inch band over the seed row, charcoal coated seed at either 4:1, 6:1, or 8:1 charcoal weight:seed weight ratios, and non‐treated seed. Sub‐plot treatments consisted of five herbicide treatments: atrazine, metolachlor, metolachlor plus atrazine, imazapic, and an untreated control. In experiment I, fluxofenin did not safen switchgrass seeds from these herbicides. In experiment II, charcoal treatments safened switchgrass seed in 2 of 4 years, when precipitation was above normal, but failed to safen switchgrass seed when rainfall was below average. In addition, switchgrass ground cover at end of season was generally below the minimum 40% threshold; therefore improved establishment techniques are still needed for switchgrass.

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