Comparing rates of mineral oil, sulfur, and phosphorous acid on Microdochium patch suppression and turfgrass quality.

Microdochium patch is a turfgrass disease caused by the fungal pathogen Microdochium nivale (Fr.) Samuels and I.C. Hallett that occurs in climates similar to the cool, humid regions of North America's Pacific Northwest. Mineral oil, S, and phosphorous acid (H₃PO₃) have been shown to suppress Microdochium patch on annual bluegrass (Poa annua L.) putting greens in western Oregon. Previous research using rates of 19.9 kg mineral oil ha^-1 applied every 2 wk alone or as a tank mixture with 12.2 kg S ha^-1, 3.7 kg H₃PO₃ ha^-1, or both resulted in unacceptable turfgrass thinning. The objective of this field experiment was to evaluate whether tank mixes of these products would suppress Microdochium patch and yield acceptable turfgrass quality when rates of mineral oil were reduced from 19.9 to 10.0 kg ha^-1, S from 12.2 to 6.1 kg ha^-1, or H₃PO₃ from 3.7 to 1.8 kg ha^-1. In both years of the experiment, all treatments suppressed Microdochium patch to <2% disease compared to more than 40% disease in the non-treated control. Mineral oil applied with S resulted in a larger loss of green cover compared to mineral oil applied with H₃PO₃ regardless of rate. These results suggest that tank mixing mineral oil and S should be avoided in the winter months. Further research studying the mitigation of green cover loss associated with these treatments is warranted. [ABSTRACT FROM AUTHOR]