Pesticide bans in Canada have resulted in a requirement for municipal turfgrass managers to use cultural methods of weed control to provide a safe playing surface for athletes. A field study was conducted to determine if overseeding provides enough competition to decrease weed populations in Kentucky bluegrass athletic turf typically used in municipal parks for recreation. Perennial ryegrass was overseeded at 2, 4, and 8 kg/100 m(2) in May, July, or September, and all permutations of these timings in nonirrigated and irrigated trials at the Guelph Turfgrass Institute (GTI) field station in Guelph, and on in-use soccer fields at the University of Guelph campus and in the town of Oakville, Ontario, Canada over 2 yr. Plant cover by species was recorded every other month using a randomized point quadrat method throughout the growing seasons of 2005 and 2006. Weed populations were not affected by overseeding in 2005, a dry growing season. However, when weed populations were high and normal growing conditions existed in 2006, overseeding applications in May/July/September at 4 and 8 kg/100 m(2) decreased perennial weed cover, specifically white clover in the irrigated trial and dandelion in the nonirrigated trial at the GTI. An increase in perennial ryegrass was observed in all plots that received an overseeding treatment. Treatments applied on the in-use soccer fields in Oakville and Guelph, which included May/September and May only overseedings, had no effect on weed populations or perennial ryegrass populations compared to the weedy control. Over the short term, high-rate and frequent overseeding with perennial ryegrass appears to provide competition against perennial weeds when weed cover is high and should be considered an important part of a weed management program for municipal turfgrass managers.
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