The Effects of Dazomet on Annual Bluegrass Seed Viability

Abstract

A major concern regarding creeping bentgrass (Agrostis stolonifera) putting greens is annual bluegrass (Poa annua) invasion. With methyl bromide fumigation now being highly restricted, alternatives must be investigated to curtail weed seed soil infestations. Currently, dazomet is the only fumigant labeled for annual bluegrass control in turfgrass systems. Therefore, research questions related to dazomet efficacy come to the forefront such as how soil texture and depth of seed bank affect efficacy as well as which application rate is most effective within a soil. A study was designed to garner data as to the depth of soil removal needed to reduce annual bluegrass seedling emergence in a newly renovated putting green. Research was conducted in different seasons, summer and fall, respectively; to evaluate seedling emergence across five soil removal depths in four sampling sites. Cores were collected from four golf courses in southeastern Michigan, subdivided into different soil removal depths, potted in sterile soil media, and established in a growth chamber. Results suggest that excavating soil to a depth of 2.54 cm, or more prudently, 3.81-cm depth could minimize annual bluegrass competition in a creeping bentgrass putting green, e.g., annual bluegrass emergence was observed to be greatest in the upper soil depths (1.27 to 3.81cm) in both seasons with minimal emergence (<1.1 plants/0.0186 m²) below the 5.08-cm soil removal depth treatment. In order to determine the effectiveness of dazomet deep within a soil, eighty glass jars (0.945 L) were filled with soil, a loamy sand and sandy clay loam, and 220 seeds of annual bluegrass (placed in a nylon mesh bag to ease retrieval) were buried at depths of 3.0 cm and 6.0 cm. Dazomet treatments consisted of the following: 294, 439, 588 kg•ha^-1, a negative control (no fumigation), and a positive control (autoclaved seed and soil at ~121 °C). Irrigation was applied at an equivalent rate of 2.54 cm•d^-1 of water to activate and incorporate the fumigant within the soil profile. All treated jars were then sealed with metal lids and subjected to a 21-d fumigation exposure period at ~25° C in darkness. Afterward, the nylon-bagged seeds were recovered, and 2,400 seeds were warm germination tested in paper-blotter-lined petri dishes to determine the effects of dazomet on seed mortality. Data results indicate that regardless of the rate of fumigation, seedling emergence was suppressed in both soil types and seed placement depths. The simulated high-barrier tarping and standard water sealing methods increased dazomet efficacy against seed germination and seedling emergence. Therefore, it may be reasonable to assume that dazomet is a highly viable fumigant to control annual bluegrass seed infestations in turfgrass systems.