Sleeper thistles in New Zealand status and biocontrol potential

Abstract

Globally the thistle tribe Cardueae (Asteraceae) contains approximately 2500 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 quot;sleeper weedsquot; 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 economicallyvalued exotic species