Irrigation Quantity Effects on Anthracnose Disease of Annual Bluegrass

Abstract

ABSTRACTIrrigation can influence both turf vigor and playability of putting greens. Anthracnose (Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman) has become an increasingly destructive disease of annual bluegrass (ABG) [Poa annua L. f. reptans (Hausskn.) T. Koyama] putting greens, particularly when turf is under stress. This 3‐yr field study evaluated the effects of irrigation quantity (100, 80, 60, and 40% of reference evapotranspiration [ETo]) on anthracnose severity of ABG mowed daily to 3.2 mm. Severe drought stress (40% ETo) increased anthracnose severity in 2006, 2007, and 2008. Anthracnose was less severe under 60% ETo irrigation, and irrigating at 80% ETo reduced severity compared to 60% ETo Irrigating at 100% ETo initially reduced anthracnose severity compared to 40% ETo; however, 100% ETo resulted in similar disease severity later in the 2006 and 2008 seasons. While this response was not observed late in the 2007 season, plots maintained at 100% ETo had turf quality similar to plots irrigated at 40% ETo later in each year due in part to increased algal development. Irrigation to replace 80% ETo typically resulted in the least amount of disease and the best turf quality throughout the trial. Thus, irrigation to minimize drought stress while also avoiding continuous high soil water content is beneficial in reducing anthracnose and maintaining acceptable turf performance.