Nitrogen Fertility, Mowing Height, and Topdressing Effects on Anthracnose and Playability of Annual Bluegrass.

Anthracnose disease of annual bluegrass (ABG; Poa annua L.) putting greens, caused by Colletotrichum cereale Manns, can be suppressed by increasing N fertility, mowing height, and sand topdressing. Interactive effects of these practices on disease severity and playability [e.g., ball roll distance (BRD)] of ABG turf remain unknown. A field trial was initiated in 2012 in North Brunswick, NJ to evaluate the effects of mowing height, N fertility, and sand topdressing on anthracnose severity and playability of ABG turf. Treatments were arranged in a 2 x 2 x 2 factorial using a split-split-plot design with four replications. Main plots were mowing height (2.3- and 3.2-mm), subplots were N fertility (100 and 200 kg ha^-1 yr^-1), and sub-subplots were sand topdressing (46.4 and 97.6 Mg ha^-1 yr^-1 during 2012; 36.6 and 80.6 Mg ha^-1 yr^-1 during 2013). As expected, increased N fertility, mowing height, and sand topdressing reduced disease severity; reported as the area under the disease progress curve (AUDPC). Nitrogen fertility accounted for 82 and 35% of the variation in AUDPC during 2012 and 2013, respectively. Sand topdressing and mowing height accounted for smaller, but similar amounts of variation in AUDPC. The relative importance of management factors for BRD differed from that observed with AUDPC responses. Increased mowing height had a substantial negative effect on BRD; whereas, greater N fertility and sand topdressing had a minimal effect. Interactions have been limited, but occasionally greater sand topdressing produced more dramatic reductions in disease severity or increases in BRD when combined with lower N or lower mowing. These findings suggest that priority should be given to lowering mowing height rather than reducing N fertility or sand topdressing rates to increase BRD without greatly increasing the risk for anthracnose. Results for the third year of this study will be reported.