Assessing Different Rates and Combinations of Sulfur, Phosphorous Acid, and a Mineral Oil to Reduce the Incidence of Microdochium Patch on an Annual Bluegrass Putting Green.

Microdochium patch (Microdochium nivale), is a turfgrass disease that affects annual bluegrass putting greens in the Pacific Northwest. Because of recent legislation, golf course superintendents are seeking fungicide alternatives to manage this disease. Previous research has suggested that the incidence of Microdochium patch could be mitigated by using a combination of a mineral oil with either sulfur or phosphorous acid, although these combinations led to abiotic damage during the winter months. The objective of this field trial was to elucidate if reducing the previously reported rates of a mineral oil, sulfur, or phosphorous acid could eliminate any abiotic damage and continue to diminish the incidence of disease. A field experiment on a sand-based annual bluegrass putting green in Corvallis, OR was repeated over two years in the absence of traditional fungicides. The trial was initiated in the fall of 2015 and concluded in the spring of 2017. Experimental design was a randomized complete block design replicated four times. Treatments were applied every two weeks and included 6 Kg sulfur, 12 Kg sulfur, 1.83 Kg H₃PO₃ or 3.66 Kg H₃PO₃ Ha^-1 in combination with either 9.97 or 19.94 Kg mineral oil Ha^-1 in addition to a non-treated control. Golfer traffic, representing 76 golf rounds a day, was simulated by walking over the plots 5 days a week. Response variables included turf quality and area under disease progress curve. No treatment provided both disease control and acceptable turf quality. All treatments including 19.94 Kg mineral oil Ha^-1 or sulfur suppressed the incidence of Microdochium patch, however these treatments also resulted in unacceptable abiotic damage. A 9.97 Kg mineral oil Ha^-1 treatment in combination with either 1.83 Kg H₃PO₃ or 3.66 Kg H₃PO₃ Ha^-1 did not result in abiotic damage, however disease (less than 2%) was still observed, leading to unacceptable turf quality.