Influence of Scarification Depth on Anthracnose Severity of Annual Bluegrass.

Although not required for infection, wounding has been reputed to enhance anthracnose (caused by the fungus Colletotrichum cereale Manns) of annual bluegrass [ABG; Poa annua L. f. reptans (Hausskn) T. Koyama] turf.  Research on the effect of wounding on anthracnose severity of ABG is limited.  In particular, any influence of mechanical injury from scarification (vertical cutting) on disease severity remains unclear.  A field study was initiated in North Brunswick, NJ on ABG turf (mowed at a 2.8-mm height) to evaluate the effect of scarification depth (1.3- and 7.6-mm) on anthracnose severity.  The trial used a CRD with ten replications and plot size of 0.5- by 1.5-m.  Treatments were applied with a scarifying reel having 1.5-mm wide blades with a 40-mm lateral spacing.  After treatments were applied (23 July 2010 and 6 July 2011), transects were established directly over the scarification lines of treated plots and randomly positioned over turf in non-scarified plots.  Disease observations were made at 10 positions along each of three 25-cm transects within each plot (30 observations per plot).  All transect-observations were performed at the same 30 locations within each plot.  Disease severity was evaluated immediately after scarification and every 1- to 5-d through Aug. 2010 and 2011.  Disease severity was 5% at the initiation of the trial in both 2010 and 2011.  Over 10 observation dates in 2010, there was one difference between treatments; deep scarification (7.6 mm-depth) had slightly (3%) greater disease severity than the control 7-d after scarification was applied.  As of mid-July 2011, no differences were observed between treatments.  The trial will be repeated for a third time during late summer 2011.  To date, findings do not support the hypothesis that mechanical injury from scarification increases anthracnose severity.