Bermudagrass (Cynodon sp.) accounts for ≈33% of managed turfgrass areas on golf courses in the United States, and is predominantly grown in the southeast, southwest, and transition zone (Lyman et al., 2007). In these areas, it is the predominant turfgrass species selected for use on golf course fairways and tees due to its superior drought, heat, and traffic tolerance, as well as its fine texture, dense canopy, and excellent performance at low mowing heights (Turgeon, 2008). Despite these positive attributes, golf course superintendents sometimes renovate bermudagrass areas, at which point its hardy, perennial growth habit may be problematic due to contamination of the successive stand (Doroh et al., 2011). Contamination from previously planted grasses can adversely affect aesthetics and functionality of the newly established turfgrass (Brosnan and Breeden, 2009).
Methyl bromide is a restricted-use pesticide that was the standard for fumigating turfgrass areas before renovation due to its superior efficacy on soilborne fungi, nematodes, and weeds; however, due to its classification as a Class I ozone-depleting substance, methyl bromide use in turfgrass systems was phased out in the first decade of the 21st century (United Nations Environment Program, 2009; U.S. Environmental Protection Agency, 2016). Due to this phase out, turfgrass managers currently rely predominantly on the nonselective herbicide, glyphosate, for bermudagrass eradication. While eradication is possible, Johnson (1988) reported three glyphosate applications (1.6 kg·ha−1 acid equivalent) over 3 months were required for 99% control 10 months after treatment. Ultimately, the time required for glyphosate–bermudagrass eradication on golf courses can result in significant revenue losses associated with the prolonged regrassing period, and potentially compromise establishment of subsequent warm-season turfgrasses by reducing the establishment period before dormancy onset.
Dazomet is a granular soil fumigant designed to be soil-incorporated by mechanical/physical or water methods. Following incorporation, dazomet reacts with water to produce methyl isothiocyanate, a gas that controls various fungi, insects, nematodes, and weeds (Brosnan and Breeden, 2009; Unruh et al., 2002). Under favorable conditions, methyl isothiocyanate formation is rapid (dazomet soil half-life <24 h), at which point it can volatilize and escape from the soil profile reducing control (Fritsch and Huber, 1995; Park and Landschoot, 2003). For this reason, management practices such as tarping and tillage are recommended to reduce atmospheric losses.
Dazomet soil incorporation via cultivation is recommended for agricultural uses; however, this practice is not desirable on wide-scale turfgrass renovations and can be problematic on certain topographies (e.g., steep slopes). In addition, dazomet soil incorporation via cultivation alone may provide unacceptable control. Unruh et al. (2002) reported dazomet (392 kg·ha−1) provided 98% common bermudagrass control in Jay, FL, 6 weeks after treatment (WAT) and 93% control 44 WAT; however, it was less effective in Arcadia, FL, as control declined to 45% and 44% on 5 and 15 WAT, respectively. The authors suggested inconsistent results might be due to nonuniform dazomet distribution in the soil profile (Unruh et al., 2002). Applicators are recommended to cover treated soil with a plastic tarp, roll it, and/or irrigate to seal fumigant vapors into the soil, which can improve efficacy and reduce off-target movement potential (Amvac Chemical Corp., 2014). Park and Landschoot (2003) reported covering the soil with a plastic tarp immediately after dazomet application at 194, 291, 340, or 388 kg·ha−1 provided ≥98% annual bluegrass (Poa annua L.) seedling reduction; however, nontarped dazomet provided ≥92% seedling reduction only at 340 or 388 kg·ha−1. The authors applied 0.5- and 0.25-inch water immediately after application in year 1 and 2, respectively, and 0.25 inch/d through 4 d (Park and Landschoot, 2003). This may have reduced annual bluegrass control in nontarped plots, as current label recommendations suggest applying 1 inch of water on the day of dazomet treatment, and up to 0.5 inch of water through the following 3 d (Amvac Chemical Corp., 2014).
Previous research has shown that applying herbicides before dazomet application can increase long-term control. Doroh et al. (2011) reported hybrid bermudagrass [Cynodon dactylon × Cynodon transvaalensis Burtt-Davy] control using dazomet may be improved by applying glyphosate (4.5 kg·ha−1) 2 weeks before dazomet application. Furthermore, glyphosate improved bermudagrass control during renovations from hybrid bermudagrass to zoysiagrass (Zoysia japonica Steud. × Zoysia matrella L.), as glyphosate fb dazomet resulted in less cover (7%) than dazomet alone (71%) at 15 weeks after establishment (Doroh et al., 2011). Contrarily, Brosnan and Breeden (2009) reported seashore paspalum (Paspalum vaginatum Sw.), a warm-season turfgrass, control was not improved following fluazifop (0.42 kg·ha−1) + glyphosate (5.6 kg·ha−1) application before dazomet application (506 kg·ha−1) compared with dazomet alone.
Although previous research has shown herbicides, irrigation, tillage, and tarping herbicides can improve bermudagrass control following dazomet application, minimal efforts have been made to evaluate all of these practices in tandem. Considering implementing such practices comes with additional expenses associated with product costs and labor, efficacious, efficient programs need to be identified. Furthermore, tarping and tillage can increase worker exposure and are not feasible in some scenarios (Branham et al., 2004). The objective of this experiment was to determine the impacts of various combinations of herbicides, irrigation, tillage, and tarping on bermudagrass control in North Carolina and Texas with dazomet.
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