Grass overseeding and a fungus combine to control Taraxacum officinale.
Common dandelion (Taraxacum officinale) is the most abundant and frequent weed within turfgrass in temperate climates. With increasing legislation, banning herbicide and non-chemical means of control are needed to replace phenoxy herbicides. The weediness of T. officinale is mainly the result of high seed production, dispersal and germination potential. A successful long-term weed control strategy should suppress established plants, exert negative effects on seed production and prevent seedling establishment. The potential of Sclerotinia minor to cause T. officinale seed mortality and reduce seedling emergence without impact on turfgrass species was evaluated in greenhouse and field experiments. Two field studies were conducted during 2004 and 2005 in Quebec, Canada. A pre-emergence application of S. minor at the time of seeding and a post-emergence application at 10 days after seeding significantly reduced T. officinale emergence to 17% and 2%, respectively, compared with 70-80% germination in the untreated control. There were no adverse effects of direct S. minor contact on turfgrass seed germination, seedling emergence or seedling establishment. Grass oversowing alone did not improve grass quality or reduce T. officinale population densities in a low-maintained lawn environment. When S. minor was combined with grass oversowing, at application or 10 days after application, a 70-80% reduction of the T. officinale population occurred in the first year, increasing to 95% in the following year in the absence of further treatments. Turfgrass appearance and quality significantly and continuously improved up to 80%, compared with 10-20% in the control plots. Densities of other weeds, white clover Trifolium repens and field bindweed Convolvulus arvensis, were also significantly reduced when S. minor was applied with grass overseeding compared with the bioherbicide alone. We have demonstrated that S. minor reduces seed numbers, seedlings and establishment of T. officinale and, when combined with grass overseeding, the grass sward flourishes and weed emergence and colonization are significantly reduced. Other broadleaf weeds are susceptible to S. minor and thus this bioherbicide could have utility in no-till maize, cereal grain and grass seed production systems, where producers are searching for non-chemical weed control.