Evaluation of Mechanisms of Spread and Control Strategies for Elephantgrass (Pennisetum purpureum).

Florida is widely considered to have great potential for biomass production because of long, mild growing seasons and abundant rainfall. Leading candidates for lignocellulose-based energy include perennial grasses, most of which are not native to Florida and some have demonstrated potential to be invasive. Elephantgrass (Pennisetum purpureum Schum.) is of major interest because it yields more biomass than other candidate grasses. Despite high yields, elephantgrass is not recommended in Florida because of its invasive potential. Studies were conducted to determine if cultivated elephantgrass types (CT) selected for use as dedicated energy crops have similar or different mechanisms of spread and response to control strategies than naturalized populations (NP) that occur as weeds. Among 10 NP and six CT, range in date of first flower was 60 d, with CT generally flowering later than NT. There was variation among CT as the earliest entry (N13) flowered 27 October while the latest (UF-1) flowered 6 December. Elephantgrass has poor seedling vigor, but all entries that set seed before frost produced seedlings in the greenhouse and field. Subsequent studies evaluated harvesting at first flower vs. at first freeze on biomass production and spread and the effect of boundary vegetation on plant growth and spread by seed. Early-flowering types yielded most if harvested at flowering vs. at first freeze, but yield of intermediate- and late-flowering types was not affected by harvest date. Plots bounded by sod yielded less than those bounded by clean-tilled soil. These data show that within P. purpureum there is potential to select late-flowering types, extending the growing season and reducing invasive potential by decreasing the likelihood of seed set before first freeze. Currently there is no evidence that harvesting at first flower reduces biomass yield, so this appears to be an effective management strategy to reduce invasive potential.