1 Lincoln University, PO Box 84, Lincoln, 7647, NZ
2 CABI Switzerland, Rue des Grillons 1, CH-2800 Delemont, Switzerland
3 Landcare Research, PO box 40, Lincoln, 7640, NZ
4 AgResearch Limited, Private Bag 4749, Christchurch, 8140, NZ
5 McClay Ecoscience, Canada
Cirsium arvense (L.) Scop. is a perennial herb indigenous to Eurasia that is now present throughout temperate regions of the world where it is considered one of the worst weeds of pastoral and agricultural systems. Classical biological control has been attempted in both North America (NA) and New Zealand (NZ). However, nearly 50 years after the first agent releases there are no indications of successful control. We retrospectively evaluate C. arvense as a target weed, critique the agents selected for release, and contrast the different situations in NA and NZ. The failure of the programme in NA is attributed to non-target impacts, and the fact that some agents either failed to establish, or had no impact on the weed. In contrast, there is a unique situation in NZ, where there are no related native thistles (Cardueae), and thus little chance of non-target impacts. In the past, the same agents that were released in NA were subsequently released in NZ, without considering whether or not these were the best choices. Thus, the past failure in NZ might be due to the previous lack of a NZ-specific approach to biocontrol of thistles in general and C. arvense in particular. A new approach taking into consideration the absence of native Cardueae has resulted in the release of agents more likely to be effective, and has potentially set NZ on track towards successful biological control of C. arvense, and other thistles.