Anthracnose Severity of Annual Bluegrass Turf As Affected by Nitrogen Form.

Increased soluble nitrogen fertilization rates have been shown to reduce the severity of anthracnose disease (caused by Colletotrichum cereale Manns) on annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] turf. However, less is known about the impact of soluble N source on this disease. The objective of this field study was to evaluate the effect of soluble-N sources applied at two application intervals on anthracnose severity during mid-season. The study was initiated summer 2010 in North Brunswick, NJ on annual bluegrass turf maintained at 3.2 mm. Nitrogen treatments were applied at 4.9 kg N ha-1 every 7- or 14-d as solutions of ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), urea (CH4N20), calcium nitrate (Ca(NO3)2), or potassium nitrate (KNO3). Results from this two-year study indicate that soluble-N source and application interval are both important factors affecting anthracnose severity. By the end of 2010, plots fertilized with nitrate sources had the lowest disease severity, while plots fertilized with sources containing ammonium had the greatest disease severity. This response, however, was not consistent with results from earlier in the season. In 2011, potassium nitrate treatments had the lowest disease severity and ammonium sulfate treatments had the greatest disease severity on all dates except the initial rating. Interaction data from 2011 indicated that there were few differences among soluble-N forms when applied every 2 weeks; whereas soluble-N form frequently impacted disease severity when applied at a weekly interval. On most rating dates in 2011, potassium nitrate applied every 7-d had significantly less disease than all other weekly treatments; whereas weekly applications of ammonium sulfate resulted in the greatest disease severity. N applied every 14-d was insufficient to suppress disease (greater anthracnose severity compared to weekly N fertilization) so it was not feasible to observe any differences among N sources at that application interval.