Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Effects of two citrus-based commercial herbicides on giant reed, Arundo donax L. (Poaceae).

Abstract

The giant reed, Arundo donax L. (Poaceae), is an invasive weed pest in the United States and other parts of the world, particularly in riparian habitats where it can hinder the flow of water and choke out indigenous vegetation. Conventional approaches to controlling A. donax have not been particularly effective, including burning, mowing, synthetic herbicides, bulldozing, and introduction of exotic biological control agents. One of the most commonly used botanically-based herbicidal compounds is d-limonene from citrus oil, but such natural, or organic, herbicides have not been assessed for their effects on A. donax. We tested two commercial citrus-based organic herbicides, BurnOut II (also contains eugenol) and Worry Free Weed and Grass Killer using topical applications at the recommended rates on mature (woody) plants, culms (lateral shoots on mature stalks that can propagate vegetatively), immature (<1 year-old) stalks, and in soil and water for effects on culm shoot and root production. Although application to mature stalks and culms growing from the stalks resulted in rapid tissue injury, the plants recovered by producing more culms at internodes and a new dominant apical meristem. Different concentrations mixed into soil and water growing substrates where culms were planted caused stunting and delays in shoot and root production. Topical application to immature stalks were effective at killing the treated stalk, but the rhizome from which multiple stalks can grow was likely not affected by the local contact action of the organic herbicides.