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 sclerotiorum for the biological control of Cirsium arvense. At each site, the experimental mycoherbicide was applied to a previously untreated plot in each 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 December significantly reduced the ground cover of C. arvense for 67, 67 and 44%, respectively of these applications Reduced ground covers ranged from 38 to 81% of the cover on untreated plots. Applications in late summer and autumn were less effective. Correlations of ground cover by C. arvense with climate parameters suggested that free moisture promoted treatment efficacy, but that intense rainfall after, treatment reduced efficacy through wash off The importance of leaf wetness for the efficacy of the mycoherbicide was confirmed by comparing disease development and mortality in C. arvense shoots with and without enhanced moisture levels under field conditions. A water miscible formulation applied as a slurry was less dependent upon leaf wetness than the dry granule formulation.