Effect of application time on the efficacy of Sclerotinia sclerotiorum as a mycoherbicide for Cirsium arvense control in pasture

An experiment was conducted in sheep-glazed pasture in three legions of New Zealand over three years to evaluate the effect of application time on the efficacy of a day granule mycelium-on-wheat formulation of Sclerotinia scl erotiorum for the biological control of Cirsium arvense. At each site, the experimental mycoherbicide was applied to a previously untreated plot in ea ch month of the year for three years at a dose of 50 g m(-2). Applications made during the spring and early summer months of October; November and Dec ember significantly reduced the ground cover of C. arvense for 67, 67 and 4 4%, respectively of these applications Reduced ground covers ranged from 38 to 81% of the cover on untreated plots. Applications in late summer and au tumn were less effective. Correlations of ground cover by C. arvense with c limate parameters suggested that free moisture promoted treatment efficacy, but that intense rainfall after, treatment reduced efficacy through wash o ff The importance of leaf wetness for the efficacy of the mycoherbicide was confirmed by comparing disease development and mortality in C. arvense sho ots with and without enhanced moisture levels under field conditions. A wat er miscible formulation applied as a slurry was less dependent upon leaf we tness than the dry granule formulation.