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New Zealand Plant Protection 66 (2013): 99-104

Sleeper thistles in New Zealand: status and biocontrol potential

M.G. Cripps, G.W. Bourd˘t and S.V. Fowler


Globally, the thistle tribe, Cardueae (Asteraceae), contains approximately 2,500 species, of which at least 339 have weed status. In New Zealand, 63 of these are present, but only nine are recognised problems, with the remainder being potential threats or "sleeper weeds". To evaluate these potential threats, the 339 global thistle weeds were ranked from most to least important, based on an assigned Index of Weed Importance, and grouped into five weed importance categories: Extreme, High, Moderate, Low and Minor. Of the global species in these categories, 94%, 56%, 28%, 19% and 7%, respectively, are present in New Zealand, and mitigating the most serious potential threats would be prudent. An option is the novel use of classical biological control agents that specialise on the thistle tribe, rather than specific target species. This is feasible for New Zealand because in the tribe Cardueae there are no natives and few economically-valued exotic species.

Keywords: Cardueae, thistles, biological control, weed management.

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