A major concern with creeping bentgrass putting greens is the high incidence of annual bluegrass invasion. A genetically diverse and prolific seed producer (Beard et al., 1978; Ellis et al., 1971; Gibeault and Goetze, 1973; Law, 1981; Timm, 1965; Tutin, 1957; Wells, 1974; Youngner, 1959), annual bluegrass thrives in highly cultured turfs (Barkworth et al., 2003; Huff, 1999; La Mantia and Huff, 2011; Warwick, 1979) and can provide a high-quality putting surface. However, most golf course superintendents consider it an invasive weed and go to great lengths to control it in their greens (Vargas and Turgeon, 2004). Previous research has not only demonstrated the colonization of distinct, aggressive populations in greens (Sweeney and Danneberger, 1995, 1997), but also the profuse quantities that remain viable in the soil seed bank (Branham et al., 2004; Peachey et al., 2001). Although some studies quantified survival of buried annual bluegrass seed in crop production fields (Peachey et al., 2001), research has not been conducted on the amount of soil removal needed to reduce seed germination in putting greens. Therefore, it is critical to determine annual bluegrass seed germination rate within soils regarding renovation practices.
Recently, golf course renovations have peaked because of aging and functionally deficient components such as putting greens (Jones, 2019), and five principles usually dictate a renovation: major turf loss resulting from abiotic and biotic stress, loss of putting green resulting from collar encroachment, excessive organic matter accumulation, need for architectural design improvement, and invasion of undesirable turfgrass species affecting surface playability (Foy and Gilhuly, 2015). In the cool-season region, conversion to a desirable grass species such as a creeping bentgrass is one option, but the cost of renovation is a big factor. Partial removal of an existing root zone—a resurfacing, as it is commonly called—is an economically viable option that costs 20% of a total rebuild (White, 2006). A complete rebuild with total root zone removal may not be the best nor necessary option in most cases. For cool-season grass species, it has been suggested that only the upper 1.0 to 3.0 inches of existing root zone be removed (Whitlark and Hummel, 2018) when replacing a turfgrass variety for an improved variety by reseeding or sodding. This removal amount (1.0–3.0 inches) would not require adding more root zone material because most putting greens older than 10 years have sufficient additions of sand topdressing, making it deeper than the original construction depth (McCarty et al., 2005; Skorulski et al., 2010; Whitlark and Hummel, 2018). These frequent sand additions have buried annual bluegrass seed deep within the root-zone profile.
Superintendents are searching for ways to improve putting surfaces not only to appease customers, but also to decrease pesticide, fertilizer, and water inputs to be more environmentally friendly (Gilhuly, 2016; Jones, 2017). Therefore, a cost-effective renovation method must be identified to reduce annual bluegrass seedling emergence in a putting green. Perhaps excavating to at least a 1.0-inch depth or, more prudently, to a 1.5- to 2.0-inch depth of an existing root zone would have sufficient efficacy to minimize weed invasion when renovating with or without soil fumigants. The objective of this study was to evaluate the effects of putting green site, soil removal depth, and season on annual bluegrass seedling emergence.
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