Evaluation of Mowing Height and Fertilizer Regime On Quality and Weed Invasion of Five Lawn Grasses.

Determining the effect of management strategies on turfgrass quality and weed invasion for various turfgrass cultivars and species is important for making management recommendations. The objective of this research was to evaluate the visual quality and weed susceptibility of several cool season lawn grasses under multiple management regimes in Wisconsin. Grasses were established in 2007 and data collected through 2010 in spring, summer and fall. The experimental design was a split-split plot completely randomized block, where five grasses were evaluated under three mowing heights (3.5, 6.0 or 8.5 cm) and three nitrogen fertilizer regimes (0, 98 or 196 kg N ha^-1 yr^-1). Lawn grasses included: ‘Kingfisher’ Kentucky bluegrass, ‘Kenblue’ Kentucky bluegrass, ‘Victory II’ chewings fescue, ‘Grande II’ tall fescue and ‘Jiffe II’ perennial ryegrass. Plots were irrigated at 80% of potential evapotranspiration weekly. Visual turfgrass quality was evaluated on a 1-9 scale, with six representing the minimally acceptable level of visual quality, and weeds were assessed using both visual estimates and point-grid methods annually. Across mowing heights, ‘Grande II’ tall fescue consistently had the greatest mean visual quality in each of the study years. Mowing at the lowest height (3.5 cm) resulted in the lowest mean visual quality of 6.2 in 2008, 5.3 in 2009 and 5.6 in 2010 across species in summer, however, mowing height effects on quality were more variable in spring and fall. The non-fertilized treatment had the lowest quality for each rating season. The 98 and 196 kg N ha^-1 yr^-1 rates were statistically similar in spring, however, the 196 kg N ha^-1 yr^-1 in summer had the greatest turfgrass quality of 7.2 in 2008, 6.5 in 2009 and 6.9 in 2010. Nitrogen affected weed pressure. The non-fertilized treatment had the greatest weed pressure of 29% in 2009 and 2010, however, not statistically different than the 98 kg N ha^-1 yr^-1 rate in 2009 (19%). ‘Grande II’ tall fescue had the lowest weed pressure of 6% in 2009 and 12% in 2010. “Kenblue” Kentucky bluegrass consistently had the greatest weed encroachment of 31% in 2009 and 28% in 2010, however, ‘Jiffe II’ perennial ryegrass in 2009 and ‘Victory II’ chewings fescue in 2010 had the same degree of weed pressure. Weeds were more prevalent at the lowest mowing height, 31% in 2009 and 38% in 2010. Generally higher mowing heights and greater nitrogen rates reduced weed pressure and increased quality. “Grande II” tall fescue had the lowest weed pressure in 2009 and 2010 and greatest quality in spring, summer and fall 2008-2010, suggesting this might be an under-utilized grass species in Wisconsin.