Switchgrass Establishment and Biomass Yield Response to Seeding Date and Herbicide Application.

Weed interference is a major challenge in the establishment of switchgrass. A field experiment was conducted in 2011-2012 and 2012-2013 growing seasons to study the influence of seeding date (November, May, June, and July) and herbicide application on switchgrass establishment, production, and weed suppression in the establishment year. Herbicide treatments were pre-emergence (PRE) application of atrazine (A) and quinclorac (Q), or PRE A+Q followed by post-emergence (POST) application of 2,4-D and dicamba. Switchgrass tiller density was increased with delaying the seeding date until July (194 tiller m^-2) in 2012; however, no significant differences in tiller density were observed among seeding dates in 2013. Switchgrass was more morphologically developed (plant height and adventitious root numbers) at earlier seeding dates (November and May) compared with later seeding dates (June and July). Weed biomass was reduced by 18% as a result of application of PRE A+Q followed by POST compared with PRE A+Q treatment. The highest weed biomass was recorded from May seeding date in both years. The highest switchgrass biomass yield was consistently obtained from May (0.87 and 1.38 Mg ha^-1 in 2012 and 2013 respectively) and June seeding dates (0.66 and 1.22 Mg ha^-1 in 2012 and 2013 respectively) whereas; July was the least productive seeding date. Our results suggested that although higher tiller density and lower weed biomass was observed with later planting date, switchgrass was more morphologically developed and produced higher biomass yield when seeded earlier. To ensure a successful long-term switchgrass establishment an early seeding date (May) and application of PRE A+Q followed by POST 2,4-D and dicamba could be a sustainable management practice.