Kentucky bluegrass (Poa pratensis L.) mixed with PRG (Lolium perenne L.) is a common seed mixture for lawn establishment. Seed mixes capitalize on the beneficial aspects of each turfgrass species such as differences in disease/insect resistance, water use efficiency, and/or traffic tolerance (Brede and Duich, 1984a; Davis, 1958; Dunn et al., 2002; Gibeault et al., 1980). The primary advantage of PRG is rapid germination and establishment (Blaser et al., 1956), providing turf cover to compete with weeds and maximize customer satisfaction when establishing a lawn. However, PRG is susceptible to numerous diseases in the humid regions of the Midwest United States and stands often thin in the heat and humidity of late summer or in winter from desiccation or extended snow cover without aggressive maintenance. Although KBG is slow to germinate and establish, it is desirable in the long term because it spreads by rhizomes, is relatively drought-tolerant, and will accommodate a wide range of management systems.
Ideally, a turf stand would be composed of equal amounts of KBG and PRG (Gibeault et al., 1980). This can be challenging in the short term because PRG germinates in 3 to 10 d and can outcompete KBG, which takes up to 28 d to germinate (Christians, 2011). Furthermore, monostands of PRG have almost twice the seedling survival as KBG (Brede and Duich, 1984a). Brede (1982) also suggests the presence of PRG may further reduce KBG seedling survival as a result of allelopathic effects. To compensate for PRG’s competitive advantage during germination, suggested seed mixtures comprise between 50% and 95% KBG by weight (Brede and Duich, 1984a; Gibeault et al., 1980; Larsen et al., 2004; Larsen and Bibby, 2005), which is between 80% and 98% KBG by seed number. In addition to the seeding ratio of PGR and KBG, several other factors may affect short-term composition of the turf stand. Date of planting and simulated sports turf traffic (Stier et al., 2008), cultivar selection (Brede, 1982), and time to initial mowing and mowing height (Brede and Duich, 1984b) have been shown to influence the short-term composition of a stand seeded with a mixture of KBG and PRG.
Furthermore, stand composition is likely dynamic as a result of the environment, pests, and/or management, and thus considerable variation is reported for the long-term composition of turf stands originally seeded as a mixture of KBG and PRG. Brede (1982) reports KBG eventually dominated a turf stand that was initially dominated by PRG in Pennsylvania. In later work by Brede (2005) in Idaho, KBG consisted of 50% to 97% of the stand 5 years after seeding 50:50 KBG:PRG (wt:wt) depending on the KBG cultivar used in the seed mixture. Conversely in Missouri, Dunn et al. (2002) reported PRG as the dominant species under simulated traffic after 5 years with initial seed ratios of KBG:PRG of 80:20 (wt:wt) regardless of irrigation regime or mowing at 1.9 or 5.1 cm. Hsiang et al. (1997) reported PRG as the dominant species after 4 years with initial seed ratios of KBG:PRG at 50:50 (wt:wt) in a study in Ontario, Canada, when mowed at 3.5 cm and irrigated to prevent drought stress.
Landscape contractors are pressured to deliver lawns from seed quickly for customer satisfaction. Therefore, lawn seed mixes including PRG at 50% or more by weight are readily available at wholesale and retail outlets. Perceived cost savings from use of PRG over KBG may also influence seed mixture composition. However, few studies have evaluated how initial composition of KBG:PRG in the seed mixture affects species composition over multiple years in the humid Midwest, just north of the transition zone of adaptability between cool- and warm-season turfgrasses. Our objective was to evaluate the establishment and species composition after 3 years of a turf stand seeded with different ratios of KBG and PRG and maintained as a lawn.
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