Seasonal Poa annua L. seedling emergence patterns in Maryland

Annual bluegrass (Poa annua L.; ABG) can be a major weed problem in golf course turf. Research-based information on the seasonal emergence patterns of ABG is limited. The objectives of this four-year field study were (i) to determine seasonal ABG emergence patterns in Maryland, (ii) to determine peak period(s) of ABG emergence, and (iii) to determine the date and estimated percentage of seedlings emerged when the rate of emergence declines. Annual bluegrass seedlings were found to emerge between August and May in two Maryland golf course roughs. A majority (50-70%) of seedling emergence occurred between late September and mid-October, and peak germination generally was observed in early October. The linear increase in ABG seedling emergence generally ended by early November; however, 24% of all seedlings emerged between November and May. No major ABG emergence cycles were observed during the spring in any year. Mean daily temperatures generally were ≤20°C during peak ABG emergence periods, and germination was stimulated by precipitation. Since the genetic diversity of ABG is well known, these findings may only be applicable to Maryland and regions with similar environmental conditions.