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

Authors: Showler, Allan; BARCO, MARGARITA - Texas State University; GOMEZ, ELIZABETH - Texas State University; SILLER, KARLA - Texas State University; Osbrink, Weste

Submitted to: Biopesticides International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2016
Publication Date: 2/2/2016
Citation: Showler, A., Barco, M., Gomez, E.L., Siller, K.M., Osbrink, W.L. 2016. Effects of two citrus-based commercial herbicides on giant reed, Arundo donax L. (Poaceae). Biopesticides International . 11:79-88.

Interpretive Summary: Interpretive Summary: The giant reed, Arundo donax L. (Poaceae), is an exotic pest of riparian and other habitats in the United States and elsewhere. Conventional tactics have not been particularly effective, including burning, mowing, synthetic herbicides, and bulldozing. A commonly used organic herbicide is d-limonene from citrus oil. We tested two commercial limonene-based organic herbicides, BurnOut II (also contains eugenol) and Worry Free Weed and Grass Killer, on mature arundo plants, lateral shoots, immature (<1 yr old) stalks, and in soil and water for effects on shoot propagation. Although the organic herbicides caused rapid tissue injury, the plants survived and continued to grow by producing new lateral shoots. Mixed into soil and water growing substrates, limonene-based herbicides caused stunting and delayed shoot and root growth. Application to immature stalks killed the stalk, but the underlying rhizome was apparently unaffected by the localized contact action of the organic herbicides.

Technical 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, and bulldozing. 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 limonene-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 yr 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.