Effect of turfgrass mowing height on biocontrol of dandelion with Sclerotinia minor

The fungus, Sclerotinia minor Jagger is under development as a bioherbicide for control of dandelion and many broadleaf weeds in turfgrass environments. The effect of S. minor on dandelion survival was evaluated under different mowing heights and compared with a commonly used herbicide Killex™. In the greenhouse, the onset of symptoms was more rapid, foliar damage was more severe, and the reduction of aboveground biomass and root biomass was greater for the bioherbicide than the herbicide. The bioherbicide reduced root biomass ≥10-fold compared with untreated plants. Under high weed infestation levels in the field, S. minor caused a greater initial reduction of dandelion density than did the herbicide during the 2-week post-application period, although reductions were greater in herbicide treated plots by 6 weeks after application. Over the growing season, S. minor and the herbicide had similar suppressive effects on dandelion density except under the closest mowing height (3-5 cm). After treatment, close mowing favored dandelion seedling recruitment and the biocontrol had no residual activity. Survival of dandelion roots was significantly less after spring than fall treatment of S. minor and season long mowing at the close height significantly reduce root survival. Close mowing may be detrimental for S. minor applications on heavily infested domestic lawns and amenity grassland areas.