Californian thistle and its variable response to the biological control agent, Sclerotinia sclerotiorum

Abstract

Californian thistle (Cirsium arvense) is a problematic weed, particularly in permanent pastures. The fungus, Sclerotinia sclerotiorum, has potential as a bioherbicide to control this weed, but its variable efficacy in historical field trials suggest that there are differences in susceptibility to S. sclerotiorum within the species. To test this hypothesis, the responses of 32 New Zealand provenances of C. arvense to a foliage-applied mycelium-on-barley preparation of S. sclerotiorum were compared under common conditions. Significant differences between provenances were found, supporting the hypothesis that there is variation within C. arvense in New Zealand in its susceptibility to S. sclerotiorum. Further work will examine differences in the efficacy of fungal isolates against different C. arvense provenances.