LAUSR

Leucanthemum vulgare, a perennial forb native to Eurasia, has become invasive in several other parts of the world. Since there is a lack of methods suitable for sustainable management of this plant across invaded landscapes, a biological control project has been initiated in North America and Australia. We evaluated the potential of the root‐feeding weevil Cyphocleonus trisulcatus as a biological control agent for L. vulgare in North America by investigating its impact on L. vulgare and studying its larval host range under no‐choice, multiple‐choice cage and open‐field conditions. Our impact experiment revealed that larval feeding by C. trisulcatus can severely damage and even kill plants. No‐choice tests conducted with 41 non‐target species showed that C. trisulcatus can develop on five closely related species. In a multiple‐choice cage test established with three of these species, the medicinal plant Matricaria chamomilla and the native North American M. occidentalis were also attacked, but to a lower degree than L. vulgare. An open‐field test conducted with four varieties of the ornamental Shasta daisy (Leucanthemum × superbum and L. × maximum) revealed similar attack on Shasta daisy as on L. vulgare. Due to the popularity of Shasta daisies, we suggest that C. trisulcatus, despite its potential to suppress L. vulgare populations, is not a suitable biological control agent for North America. However, C. trisulcatus may still be a potential biological control agent for L. vulgare in regions where Shasta daisy is less popular, such as Australia. Further host‐range tests with species native to Australia as well as with additional species important for the horticultural industry in Australia are currently under way.