Suppression of Microdochium patch using rotations of mineral oil, sulfur, and phosphorous acid

Abstract

AbstractMicrodochium patch is a turfgrass disease caused by the fungal pathogen Microdochium nivale (Fr.) Samuels and I.C. Hallett that occurs in cool, humid conditions, which are commonplace in the U.S. Pacific Northwest and northern Europe. Pesticide restrictions in certain areas make suppressing Microdochium patch challenging, and alternative control methods are desired. Previous research has shown that mineral oil, S, and phosphorous acid (H3PO3) suppress Microdochium patch, but abiotic damage was associated with repeated mineral oil applications. Two field experiments in western Oregon focusing on the suppression of Microdochium patch and turfgrass quality on annual bluegrass (Poa annua L.) greens are presented. The first experiment compared tank mixtures of mineral oil and S or mineral oil and H3PO3 in rotation with a tank mixture of S and H3PO3. The second experiment focused on seasonal rotations that excluded mineral oil in certain months and compared 2‐ and 3‐wk application frequencies. All rotations, in both experiments, suppressed Microdochium patch compared to the non‐treated control, although differences in turfgrass quality were observed. In the first experiment, green cover percentage was used to assess abiotic damage. A mineral oil and H3PO3 tank mixture rotated every 2 wk with S and H3PO3 resulted in the highest green cover percentage. In the second experiment, most of the applications made every 2 wk completely suppressed Microdochium patch. Two treatments applied every 2 wk that withheld mineral oil in the winter months resulted in turfgrass quality ratings considered acceptable for putting greens on all rating dates.