The Potential Allelopathic Characteristics of Bitter Sneezeweed (Helenium amarum)

Abstract

Research was conducted to determine the potential for allelopathy to occur in pastures infested with bitter sneezeweed. Aqueous extracts of bitter sneezeweed leaves reduced alfalfa and Italian ryegrass seedling growth as much as 50% at concentrations of 0.5% (w/v). Leaf extracts were more phytotoxic than either stem or root extracts and seedling growth was reduced more than seed germination. Bitter sneezeweed tissue mixed in potting soil at concentrations as low as 0.3% w/w reduced alfalfa seedling numbers by 43%, plant height by 26%, and foliage dry matter production by 54% compared to plants cultured in soil without bitter sneezeweed leaf tissue. The potential concentration of bitter sneezeweed leaf material in soil in the pasture ecosystem was determined to be 0.5% w/v in the liquid phase and 0.2% w/w in the solid phase. Alfalfa seedling growth was reduced by 70% when germinating seed were placed under a bell jar with a potted mature bitter sneezeweed plant compared to control seedlings. A potential exists for bitter sneezeweed interference with developing alfalfa and Italian ryegrass seedlings following fall interseeding into pastures infested with bitter sneezeweed.