Topdressing Incorporation and Sand Shape Effects on Anthracnose Severity of Annual Bluegrass.

Sand topdressing is a common practice on putting green turf and is suspected to enhance anthracnose (Colletotrichum cereale Manns) disease. This study evaluated topdressing incorporation method (none, vibratory rolling, soft bristled brush and stiff bristled brush) and sand shape (none, round and sub-angular) for effects on anthracnose severity in 2006 and 2007. A split-plot design with incorporation method as the main plot factor and sand shape as the subplot factor was used on a 5-yr-old annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] turf mowed at 3.2 mm. Topdressing was applied at 0.3 L m^-2 every 14-d from 27 June and 14 May to 13 and 27 September 2006 and 2007, respectively. Disease severity was measured as the percent area with symptomatic turf. The sand shape main effect was the only significant source of variation in both years. Both sand shapes initially increased disease severity 4 to 14% compared to non-topdressed turf in July 2006; whereas neither sand shape increased severity compared to non-topdressed turf in July 2007. Sub-angular and round sands reduced anthracnose 8 to 29% and 7 to 29%, respectively, compared to non-topdressed turf during August and September of 2006 and 2007. Anthracnose was less severe in plots topdressed with sub-angular sand than round sand in July 2006 and July through September 2007. These commonly used topdressing incorporation methods did not affect anthracnose severity and cumulative sand topdressing reduced disease severity particularly with sub-angular shaped sand.