Photograph Caption: Early results of a USGA-funded research project at Rutgers University strongly suggest that a weekly application of potassium nitrate during the growing season reduces anthracnose disease severity. Anthracnose first appears on annual bluegrass as 1/4 to 1/2-inch diameter spots of yellow to orange-brown turf. In a short time, the small spots can progress into large, irregularly shaped areas on infected putting greens, tees, or fairways. Infection often occurs first on older leaves of plants, causing yellow leaf lesions.
Anthracnose is a common fungal disease of annual bluegrass putting greens in the United States. Previous USGA-funded research at Rutgers University found that increasing ammonium nitrate rates up to 0.2 lbs. of nitrogen per 1000 ft 2 per week during the growing season reduced anthracnose severity compared to lower nitrogen rates. A new USGA study at Rutgers University looked at the applied nitrogen source effect on the severity of anthracnose outbreaks. The five soluble-nitrogen products tested include ammonium sulfate, ammonium nitrate, urea, calcium nitrate, and potassium nitrate applied at 0.1 lbs. of nitrogen per 1000 ft 2 every 7 or 14 days. This three-year field trial was initiated spring 2010 in North Brunswick, N.J. on an annual bluegrass putting green maintained at a 0.125 inch height of cut. In general, potassium nitrate treatments had the lowest anthracnose severity; whereas, ammonium sulfate treatments had the greatest anthracnose severity. Application frequency also had a significant impact on disease severity throughout the study. Weekly applications of soluble nitrogen consistently reduced disease severity compared to biweekly applications. The biweekly applications of all soluble nitrogen sources tested did not provide a sufficient amount of nitrogen to reduce anthracnose severity. The early results strongly suggest that weekly applications of potassium nitrate were required to significantly reduce anthracnose severity.
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