Mowing and rolling strategies to manage anthracnose on annual bluegrass greens

John C. Inguagiato, Ph.D. James A. Murphy, Ph.D. Bruce B. Clarke, Ph.D. Anthracnose, caused by the fungus Colletotrichum cereale (2), has become a common disease of annual bluegrass (Poa annua) and, to a lesser extent, creeping bentgrass (Agrostis stolonifera) greens throughout the world (9). The disease may occur as a basal rot of necrotic, watersoaked crown tissue at any time of the year or as a foliar blight during high summer temperatures (17). Both types of anthracnose typically start as 0.25to 0.50-inch (0.64to 1.27-centimeter) chlorotic (yellow) patches that coalesce to affect larger areas of turf. Black to brown reproductive structures (acervuli) containing crescent-shaped, single-celled spores and hairlike spines (setae) on infested tissue are diagnostic signs used to identify this disease. Control of anthracnose epidemics is complicated. Many parts of the country have reported the presence on greens of C. cereale isolates that are resistant to a number of fungicide classes that have suppressed anthracnose in the past (9). Furthermore, anthracnose is more severe on stressed turf (9), and cultural practices employed to improve playability (that is, green speed or ballroll distance) are thought to enhance this disease by increasing plant stress. Insufficient nitrogen fertilization is known to increase anthracnose severity on annual bluegrass greens (4). However, it is not known how other cultural practices used to manage green speed affect anthracnose severity. Mowing height is inversely related to green speed, a common measure of putting green playability (8). Cursory studies have demonstrated that anthracnose incidence and severity increases at lower heights of cut (1,10), although we have yet to determine the effects of mowing height combined with different mowing frequencies or lightweight rolling on anthracnose and green speed. Mowing frequency can be increased (that is, daily double-cut) to improve green speed (8). However, increased mowing frequency may reduce root mass and carbohydrate reserves (5) and increase damage (wounding) to leaf tissues, possibly enhancing infection by C. cereale (9). Lightweight rolling is another practice used to increase green speed by smoothing and improving uniformity of the turf canopy (8). Rolling more than three times per week reduced turf quality in