A Sulfur and Phosphorous Acid Combination Applied in Rotation with 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. Recent legislation has led managers to seek alternatives to fungicides to mitigate turf disease. Research has suggested that a combination of sulfur and phosphorous acid applied every two weeks reduced the incidence of Microdochium path although not to levels considered acceptable for golf course putting greens. Other research has suggested that mineral oil applied in combination with either sulfur or phosphorous acid reduced the incidence of Microdochium patch, although unacceptable abiotic damage was observed. The objectives of this current field trial were to assess the use of a sulfur and phosphorous acid combination in rotation with applications including horticulture oil to quantify any reductions in the incidence of Microdochium path and to quantify any abiotic damage resulting from the treatment combinations. A field experiment from October to April was repeated over two years beginning in 2015 and ending in 2017 on a sand-based annual bluegrass putting green in Corvallis, OR in the absence of traditional fungicides. The trial was a randomized complete block design replicated four times with four different treatments applied every two weeks. Treatments included a 12 Kg sulfur Ha^-1 and 3.66 Kg H₃PO₃ Ha^-1 combination applied every two weeks or in rotation with a 19.94 Kg mineral oil Ha^-1 applied in combination with either 12 Kg sulfur Ha^-1 or 3.66 Kg H₃PO₃ Ha^-1 along with a control. Traffic simulation of 76 golf rounds per day was applied by walking over the plots. Response variables included, abiotic damage assessment, turf quality and area under disease progress curve. A sulfur and phosphorous acid combination in rotation with a horticulture oil and phosphorous acid combination reduced disease incidence and resulted in acceptable turf quality during both years of the trial.