The Effects of Sulfur Rates and Calcium Sources on Microdochium Nivale and Annual Bluegrass Health.

In the Pacific Northwest, with nine months of cool, wet weather, repeated fungicide applications have historically been used to control Microdochium nivale on annual bluegrass (Poa annua L.) putting greens.  However, there is increasing concern associated with pesticide use resulting in a growing number of bans and restriction.  Under this regulatory environment the exploration for alternative methods of disease mitigation is necessary.  Therefore, the objective of this research was to determine if sulfur applied with and without various calcium sources can reduce the number of annual fungicide applications necessary to manage M. nivale on annual bluegrass without being detrimental to turf health.  A three year field trial was initiated in September of 2013 at the Oregon State University Lewis Brown Farm in Corvallis, Oregon on an annual bluegrass putting green.  This experiment was a randomized complete block design, with four replications.  Factors included elemental sulfur rates (0, 146, and 292 kg/ha per application) applied monthly, and calcium sources (none, calcium carbonate, calcium sulfate, and calcium phosphate) applied in the spring and fall with coring at 584 kg/ha product per application.   A scout and treat approach was initiated in the fall of each year and fungicide applications [Banner Maxx II (propiconazole) at 6.4 L/ha mixed with Turfcide 400 (pentachloronitrobenzene) at 19.1 L/ha] were applied curatively on a per plot basis when an action threshold of 5 small spots or one spot exceeding 2.54 cm in diameter was reached.   Response variables included turf quality, the number of curative fungicide applications made a season, and Anthracnose severity.  The sulfur applications reduced the number of fungicide applications with the highest rate requiring the fewest applications.  However, turf color ratings were reduced by sulfur applications.  Observations recorded in the summer months also determined that sulfur applications increased Anthracnose severity.