Turfgrass renovation using dazomet to control the Poa annua L. soil seed bank

Annual bluegrass (Poa annua L.) is an invasive weed producing copious amounts of viable seed that compete with seedling turfgrasses during renovation. These field studies were conducted to determine the effectiveness of dazomet (tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione), a granular soil sterilant that breaks down in soil to release methyl isothiocyanate (MITC), for controlling the soil seed bank of annual bluegrass during turfgrass renovation. Field trials in Urbana, Ill., and West Lafayette, Ind., in Spring and Fall 2000 and 2001 evaluated dazomet rate from 0 to 504 kg·ha^-1 and soil preparation techniques to determine the most effective practices to reduce annual bluegrass reestablishment into a creeping bentgrass (Agrostis stolonifera L.) seeding. The interval, in days, between dazomet application and creeping bentgrass planting was also examined to determine the optimal seeding time as measured by the level of annual bluegrass reestablishment. Spring trials generally gave poor results that were attributed to windy conditions resulting in rapid loss of MITC. The annual bluegrass soil seed bank was reduced 46% in spring trials compared to 78% in fall trials. Increasing dazomet rates reduced the absolute number of viable annual bluegrass seeds remaining in the soil. However, significant quantities of viable seed remained, regardless of dazomet rate. Annual bluegrass infested the renovated turf in all trials to varying degrees. Dazomet rates of 420 or 504 kg·ha^-1 yielded the lowest rates of annual bluegrass reestablishment. Trials conducted in the fall at these rates resulted in annual bluegrass cover of 1% to 20% in the resulting turf. Creeping bentgrass planted at 1 day after dazomet application had significantly less annual bluegrass than when seeded at 7 or 9 days after dazomet application. Dazomet is a tool that can help reestablish a new turf with lower levels of annual bluegrass. However, eradication of annual bluegrass with dazomet is not likely and environmental conditions will dramatically affect the success of the sterilization.