Terbutryn resistance in Vaucheria dichotoma

Abstract

Infestations of Vaucheria dichotoma have been reported to become resistant to the herbicide terbutryn after successful control by annual or biennial applications for 11 years. V. dichotoma was isolated from a site where terbutryn treatment gave good control and from a site where terbutryn treatment had failed. The isolate from the latter was resistant to terbutryn in laboratory toxicity tests. The resistant strain was not killed until the dose of terbutryn was increased to more than double the concentration approved for use in British waters. The shape of the resistance curve indicated that the resistance mechanism was not by modification of the protein binding site, suggesting that differential uptake, translocation and/or degradation is involved.