Anthracnose Severity On Annual Bluegrass Turf as Affected by Spring and Summer Topdressing.

Anthracnose is a destructive disease of annual bluegrass [ABG; Poa annua L. f. reptans (Hausskn) T. Koyama] turf caused by the fungus Colletotrichum cereale Manns.  Increased frequency and severity of this disease on putting greens over the last fifteen years has been attributed, in part, to stress-inducing management practices.  Previous research has indicated that sand topdressing of ABG turf during the summer can reduce anthracnose severity but the effect of spring topdressing on this disease has not been examined.  A field study was initiated in North Brunswick, NJ to evaluate the effect of spring topdressing (0, 1.2 and 2.4 L m^-2 applied as two split-applications on 20 April and 4 May 2009, and 14 and 28 April 2010) as well as the potential for this factor to interact with the effects of summer topdressing (0, 0.075, 0.15, 0.30 and 0.6 L m^-2 every 14-d from 1 June to 24 August 2009, and 24 May to mid-August 2010) on anthracnose severity.  The trial used a 3 x 5 factorial arranged as a RCBD with four replications and was conducted on ABG maintained at 3.2 mm on a Nixon sandy loam.  Disease severity reached 10% on all treatments by early-August 2009 and mid-May 2010.  Both spring and summer topdressing significantly reduced disease severity compared to no topdressing.  Spring topdressing at 2.4 L m^-2 was more effective at suppressing disease than 1.2 L m^-2.  Generally, a summer topdressing rate of 0.30 L m^-2 every 14-d was required to reduce disease severity.  The summer topdressing effect was more consistent than the spring topdressing effect in 2009, whereas spring topdressing was more consistent in 2010.  The practice of spring and summer topdressing can be used by turf managers as a tool to reduce anthracnose on ABG putting greens.