Golf Course Management

MAR 2019

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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03.19 GOLF COURSE MANAGEMENT 73 Controlling silvery-thread moss (Bryum argenteum Hedw.) infestations in putting greens can be difficult because of the moss's unique morphological and biological proper - ties. Silvery-thread moss is a perennial species capable of tolerating a wide range of envi - ronmental conditions and is highly competi- tive during low temperatures (2, 5), when the relative growth rate of desirable cool-season turfgrass species is low. A silvery-thread moss infestation typically begins as small colonies (< 2 inches [5 cm] in diameter), but infesta- tions can rapidly increase in size if environ- mental conditions are conducive to its growth and dispersal. Dispersal and growth Silvery-thread moss can invade new habi - tats via production of sexual and asexual structures, but once established, it is believed to spread exclusively through asexual struc - tures (11, 13). Two common modes of asexual reproduction are fragmentation and bulbil production (3, 13). Fragmentation is the phys - ical movement of an existing silvery-thread moss shoot. Bulbils are highly condensed leaf primordia and are actively produced by an existing silvery-thread moss shoot. Shoot fragments and bulbils are important mecha - nisms of dispersal because both are readily transported by machinery and water. Left unchecked, a small infestation can quickly spread throughout a putting green via these asexual structures, making it imperative to take action early in an infestation. Standard golf course management prac - tices often affect the population dynamics of silvery-thread moss in a creeping bentgrass putting green. For example, mowing at 0.125 inch (3.2 mm) resulted in a 1.6-fold increase in silvery-thread moss severity over mowing at 0.157 inch (4.0 mm) (4). After investigating different nitrogen sources, researchers discov - ered that soluble nitrogen sources increased silvery-thread moss severity in greens (10, 16). Irrigation practices may also influence silvery- thread moss invasion. Silvery-thread moss es - tablishment was found to increase with higher irrigation frequencies in greenhouse experi - ments (6), but several light topdressing appli- cations were shown to reduce silvery-thread moss severity slightly (1). Finally, applications of the herbicide carfentrazone (QuickSilver, FMC Corp.) can selectively suppress silvery- thread moss in creeping bentgrass (1, 4, 15). Different combinations and intensities of these practices are likely to affect the success of silvery-thread moss control measures. Cultivation practices Little is known, however, about the effect of turfgrass cultivation on silvery-thread moss severity in putting greens. Aerification and vertislicing are commonly used to manage thatch and compaction and to increase water infiltration. Both practices create temporary openings in the turfgrass canopy, which may be recolonized by either silvery-thread moss or creeping bentgrass, but it is unclear which spe - cies will ultimately occupy the available sites. Personal observations indicate creeping bent - grass has a difficult time recolonizing an area currently occupied by silvery-thread moss, be - cause stolons and tillers cannot penetrate the dense gametophyte. Aerification and verti - slicing can create available sites within the moss gametophye, which would allow neigh - boring creeping bentgrass plants to establish; conversely, silvery-thread moss propagules may reside in the available sites and further the infestation. Unfortunately, no published research has evaluated the effect of aerification or vertislicing on an existing silvery-thread moss infestation. When used in conjunction with aerifica - tion or vertislicing, applications of sand top- dressing might give creeping bentgrass a com- petitive advantage in colonizing available sites by suppressing silvery-thread moss growth (1). Similarly, applications of carfentrazone have been shown to be highly effective at suppress - ing silvery-thread moss growth (1, 4, 15), and, thus, may also be a valuable tool for shifting the population dynamics in favor of creeping bentgrass when aerification and/or vertislicing are implemented. erefore, the objective of our study was to determine the effect of cultivation — with and without light, frequent topdressing and carfentrazone — on an existing silvery-thread moss infestation in a creeping bentgrass put - ting green. We hypothesized that cultivation would reduce silvery-thread moss cover when used in conjunction with carfentrazone or topdressing, but would increase silvery-thread moss cover when implemented as a stand- alone practice. Materials and methods A two-year field experiment was con- ducted from October 2012 to October 2014 at the Rocky Ford Turfgrass Research Cen - ter in Manhattan, Kan. Treatments were ap- plied to a Penncross creeping bentgrass put- ting green with an existing silvery-thread The research described in this article was carried out at Kansas State University's Rocky Ford Turfgrass Research Center in Manhattan, Kan.

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