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Does Stem Injection of Glyphosate Control Invasive Knotweeds (Polygonum spp.)? A Comparison of Four Methods

Published online by Cambridge University Press:  20 January 2017

Erin N. Hagen
Affiliation:
College of Forest Resources, University of Washington, Box 352100, Seattle, WA 98195
Peter W. Dunwiddie*
Affiliation:
The Nature Conservancy, 1917 1st Ave., Seattle, WA 98101
*
Corresponding author's E-mail: [email protected]

Abstract

Japanese knotweed, Sakhalin knotweed, and their hybrid, Bohemian knotweed, are invasive across much of the United States. Monocultures formed by these species threaten natural riparian areas, and effective methods of control are being sought. Injection of herbicide is a relatively new control technique with no known published results. Bohemian knotweed was injected with four treatment dosages: 1 ml (0.03 oz) (0.48 g ae) (0.017 oz ae), 3 ml (0.10 oz) (1.44 g ae) (0.05 oz ae), or 5 ml (0.17 oz) (2.4 g ae) (0.08 oz ae) of undiluted glyphosate (suggested application), and 5 ml (0.17 oz) of a glyphosate : water mix (1 : 1, by vol) (1.2 g ae) (0.04 oz ae). Injections were tested at two heights on the plants: low node, 0.2 m (0.66 ft) (L) or chest height node, 1.0 to 1.3 m (3.3 to 4.3 ft) (M). After 1 mo, average percent injury was greater than 90%, and analysis showed no effect of injection location on the stem and no difference between the suggested 5-ml (0.17 oz) glyphosate application and 3-ml (0.10 oz) application. Nine months after treatment there was a reduction in knotweed height and density, though vigorous regrowth was evident within plots. Although the injection method results in the short-term dieback of injected stems, drawbacks to its use in certain scenarios should be considered when developing an integrated management plan for knotweed control.

Type
Research Articles
Copyright
Copyright © Weed Science Society of America 

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