The consequences of “chemical dependency” and lack of herbicide rotation have had lasting effects on annual bluegrass (Poa annua L.) management in southern and transition zone climates of the United States. In these regions, reliance on selective herbicides has resulted in evolved resistance to several sites of action, reducing the number of effective annual bluegrass control herbicides. Currently, it is the third most herbicide-resistant weed species globally (Heap, 2019). A key characteristic that contributes to the ubiquity, diversity, and widespread resistance of annual bluegrass (or any successful weed population), is its fecundity—specifically, the seedbank size and the rate at which it accumulates (Mengistu et al., 2000; Mithila and Godar, 2013; Norsworthy et al., 2012; Renton et al., 2014). In one season alone, a single population can produce hundreds of thousands of seeds per square meter (Lush, 1988). A majority of those viable reside at shallow depths (Branham et al., 2004; Green et al., 2019). To prolong the sustainability of a production system, the seedbank must be managed (Norsworthy et al., 2012). Effective seedbank management methods for turfgrass systems have not been identified. Consequently, when annual bluegrass colonizes a turf system where it is not the primary species being managed, sustainable management is often compromised. Golf course renovation is an opportune time for practitioners to mitigate the annual bluegrass seedbank. During a typical renovation, soils are either fumigated or excavated.
The only fumigant currently labeled for turfgrass systems is dazomet (Basamid G) (Basamid Granular; AMVAC Chemical Corporation, Los Angeles, CA). Manufactured as a granular fumigant, dazomet is activated by water and quickly hydrolyzes to the bioactive gas, methyl isothiocyanate (MITC) (Fang et al., 2018; Roberts and Hutson, 1999). In moist soils, dazomet and MITC are both very short-lived (Dungan et al., 2003; Fritsch and Huber, 1995; Ruzo, 2006). As the 2017 Basamid G label states, dazomet can be applied for weed control to golf course fairways at 244 to 588 kg·ha−1 when mechanically incorporated or at 244 to 294 kg·ha−1 when incorporated by water (Anonymous, 2017). For either method, irrigation must be applied immediately after application to activate the bio-active MITC and create a water seal at the soil surface. Methyl isothiocyanate is most efficacious when contained by tarp cover (Bravo et al., 2018; Park and Landschoot, 2003; Landschoot et al., 2004). Covering large-scale areas such as fairways with a tarp would be laborious, costly, and impractical. The need for tarp cover can be partially offset when a portion of seed-contaminated soil is removed before dazomet is applied (Bravo et al., 2018). However, practical excavation methods applicable to fairways have not yet been identified.
Fraise (fraize, fraze) mowing cultivation, which was originally purposed for thatch and organic matter management of athletic fields (Daily, 2016), effectively removes surface material from large areas. Functioning similar to a flail mower, a Power take-off (PTO)-driven rotor spins at a prescribed depth and removes cultivated material using a conveyor belt. One of the most prominent models today is the Koro FieldTopMaker (Campey Turf Care Systems, Cheshire, UK), which may be equipped with configurable rotors that strip or aggressively cultivate surface material at depths between 0 and 50 mm. Such innovations have expanded the application of fraise mowing to hybrid turf system grooming and hygiene, athletic field renovation, and warm-season turfgrass establishment and management (Brosnan et al., 2020; McCauley et al., 2019; Munshaw et al., 2017). No prior work has evaluated its use for cool-season golf course fairways.
Integrated weed management (IWM) programs that incorporate both chemical and mechanical strategies are an effective and sustainable approach to weed management (Buhler, 2002; Harker and O’Donovan, 2013; Swanton and Weise, 1991). In the summers of 2018 and 2019, two experiments combining dazomet fumigation and fraise mowing cultivation were conducted in Michigan. The experimental objectives were: 1) to assess the application of fraise mowing cultivation for use in cool-season fairway renovations and 2) to evaluate their combined treatment effects on annual bluegrass control and creeping bentgrass (Agrostis stolonifera L.) establishment.
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