Evaluating the Efficacy of Dazomet for the Control of Annual Bluegrass Seed Germination in Renovated Turf Surfaces
Authors: Bravo Jacob S. , Green Thomas Okada , Crum James R. , Rogers John N. , Kravchenko Sasha , Silcox Charles A. 
Published: February 2018

The soil sterilant, dazomet, is the primary product in the turfgrass industry set to take the position of methyl bromide, which is no longer available for use on turfgrass. With turf surface renovations taking place throughout the country, the need for an effective soil sterilant is critical. This study focused on the ability of dazomet to inhibit germination of annual bluegrass (Poa annua) seeds when it is used as per the current, turf focused, label which decreased legal application rates across all surfaces. This study was a four-way factorial in a split-split plot design with whole plots in a randomized complete block design arrangement with three replications. The first factor, soil type, included two levels. Soil-type plots (60 × 95 ft) were either sand capped from topdressing over the native Capac loam or they were the native Capac loam. Sand topdressing was applied biweekly at a rate of 0.14 yard3/1000 ft2, April to September since 2011; accumulating a total of 1.5 inches of sand. Each of three replicated blocks consisted of two soil-type plots. The second factor was time trials, with two levels of starting times, June and August. Each soil-type plot was split into two subplots and the trials were assigned at random to subplots within each plot. The third factor, soil preparation, involved either removing the upper 1.5 inches of the sod/soil layer or spraying plots with glyphosate and then heavily cultivating them. This cultivation included a vertical-cut and a core cultivation with an aerator using 0.5-inch hollow tines at 2 × 2-inch spacing. The fourth factor, treatment regime, comprised 11 parameters that encompassed dazomet application rate, incorporation method, and the technique used to seal the soil surface. Dazomet treatments were applied with a shaker bottle, at rates that included 262, 421, 525, and 262 lb/acre applied twice at a 5-day interval. The treatments were incorporated into the soil either through 1 inch of irrigation, through four consecutive days of irrigation following this schedule: 1, 0.5, 0.25, 0.125 inch each day after application, respectively, or physically (P) with a rotary tiller set to 1.5 inches, the depth of the topdressing layer. All P incorporated plots were hand rolled following application, regardless of the tarping procedure. Water-incorporated plots were either sealed with a clear plastic 4-mil tarp or they were left unsealed. Researchers evaluated the level of germination control by counting individual annual bluegrass seedlings using a 1 × 1-ft grid. A significant interaction occurred between soil type and soil preparation as well as between soil type and treatment. A three-way interaction also occurred between trial, treatment and soil preparation. In general, tarped treatments showed better annual bluegrass control compared with nontarped treatments. Furthermore, sand topdressed soils showed lower numbers of annual bluegrass as compared with native soils. Finally, reduced annual bluegrass germination was found in plots that had the top 1.5 inches of material removed.