Sand Topdressing Rate and Interval Effects on Anthracnose Severity of an Annual Bluegrass Putting Green

Sand topdressing has been reputed to increase anthracnose caused by Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman on annual bluegrass (ABG) [ Poa annua L. forma reptans (Hausskn.) T. Koyama] putting greens. Field trials were conducted to determine the effects of (i) frequent (7 d) and low‐rate (0.3 L m −2 ) sand topdressing and brushing, (ii) infrequent (21 and 42 d) and increased‐rate (1.2 L m −2 ) sand topdressing, and (iii) sand topdressing application intervals (7, 14, and 28 d) and rates (0.3 and 0.6 L m −2 ) on anthracnose severity of ABG turf mowed at 3.2 mm. Topdressing every 7 d at 0.3 L m −2 initially enhanced disease (8%) during the first year of the trial; however, continued topdressing reduced anthracnose severity 17 to 47% later in 2006 and 3 to 26% in 2007 compared to nontopdressed turf. Topdressing every 21 and 42 d at 1.2 L m −2 reduced disease 4 to 28% over the 2‐yr study; however, sand applied every 21 d reduced disease 5 to 13% more than the 42‐d interval in 2007. Topdressing rate (0, 0.3, and 0.6 L m −2 ) and interval (7, 14, and 28 d) interacted to affect anthracnose severity in both years. Disease declined in a curvilinear manner as rate increased at the 7‐ and 14‐d intervals each year. Increased rates applied every 28 d reduced disease linearly in 2006 and curvilinearly at rates exceeding 0.3 L m −2 in 2007. Topdressing every 7 or 14 d at 0.3 or 0.6 L m −2 , respectively, provided the most rapid and effective anthracnose reduction and best turf quality.