A review of recent research on the microbial control of Californian thistle and other pasture weeds using the fungus Sclerotinia sclerotiorum as a biological herbicide.

In this paper we review the research findings research to date indicate that S. sclerotiorum has published to date on the development of a plant pathogenic fungus, Sclerotinia sclerotiorum, as a mycoherbicide for Californian thistle, Cirsium arvense, and other weeds of pastures. A strain of the fungus isolated from Californian thistle was virulent also on Scotch thistle (Cirsium vu&are), nodding thistle (Cur&us nutans) and ragwort (Senecio jacobaea) when applied as a myceliumon- wheat formulation to the foliage of these weeds under glasshouse conditions. In field trials in which this formulation of the mycoherbicide was applied to the new spring foliage of Californian thistle in Canterbury sheep pastures, the thistle was controlled, to a high level both in the season of application and during the following growing season. Debilitation of root systems of the thistle occurs through reductions in photosynthetic capacity through death of treated shoots, and by invasion and rotting of roots by the pathogen. The strain of the fungus used in the field trials did note infect either grasses or clovers. The results of research to date indicate that S, sclerotiorum has considerable potential as a mycoherbicide for use in pastures against Californian thistle and some other species of weeds. Keywords: biological weed control, Carduus nutans, Cirsium arvense, Cirsium vulgare, mycoherbicide, Sclerotinia sclerotiorum, Senecio jacobaea