Iron sulfate and phosphorous acid affect turfgrass surface pH and Microdochium patch severity on annual bluegrass

Authors: Mattox, Clint; DUMELLE, MICHAEL - Oregon State University; MCDONALD, BRIAN - Oregon State University; GOULD, MICAH - Barenbrug West Coast Research Station; OLSEN, CONNER - Oregon State University; BRAITHWAITE, EMILY - Oregon State University; KOWALEWSKI, ALEC - Oregon State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2023
Publication Date: 5/25/2023
Citation: Mattox, C.M., Dumelle, M.J., Mcdonald, B.W., Gould, M.A., Olsen, C.J., Braithwaite, E.T., Kowalewski, A.R. 2023. Iron sulfate and phosphorous acid affect turfgrass surface pH and Microdochium patch severity on annual bluegrass. Plant Disease. https://doi.org/10.1094/PDIS-08-22-1960-RE.
DOI: https://doi.org/10.1094/PDIS-08-22-1960-RE

Interpretive Summary: Microdochium patch is a turfgrass disease that is especially problematic on golf course putting greens comprised of annual bluegrass. Previous research has shown that iron sulfate heptahydrate and phosphorous acid suppressed Microdochium patch when applied alone, although unacceptable turfgrass quality was observed. This project compared the effects of different rates of iron sulfate heptahydrate in combination with phosphorous acid on an annual bluegrass research green in western Oregon on Microdochium patch suppression and turfgrass quality. We found that lower rates of iron sulfate heptahydrate in combination with phosphorous acid suppressed Microdochium patch, resulting in comparable disease suppression and better turfgrass quality than when higher rates of only iron sulfate heptahydrate were applied. During the course of the experiment, we also observed that the products reduced the pH of the treatment spray suspensions. Using a flat-tipped pH electrode, we were able to quantify that the treatments led to a reduction in pH of the leaf surface. To test whether or not the change in pH of the leaf surface correlated with the suppression of Microdochium patch, an additional experiment explored sulfuric acid as a treatment. We observed that even though sulfuric acid reduced the pH of the leaf surface more than iron sulfate, Microdochium patch was not suppressed by sulfuric acid whereas iron sulfate treatments resulted in no disease. We concluded that the reduction in leaf surface pH was not likely responsible for suppressing Microdochium patch and that more research is needed to determine the mechanism behind the suppression of Microdochium patch by iron sulfate.

Technical Abstract: Microdochium patch is a turfgrass disease caused by the fungal pathogen Microdochium nivale. Iron sulfate heptahydrate (FeSO4•7H2O) and phosphorous acid (H3PO3) applications have been shown to suppress Microdochium patch on annual bluegrass putting greens when applied alone, although disease suppression was not adequate or turfgrass quality was reduced from the applications. A field experiment was conducted to evaluate the combined effects of FeSO4•7H2O and H3PO3 on Microdochium patch suppression and annual bluegrass quality. The results of this work suggest that the addition of 3.7 kg H3PO3 ha-1 with 24 or 49 kg FeSO4•7H2O ha-1 applied every 2 wk improved the suppression of Microdochium patch without substantially compromising turf quality, which occurred when 98 kg FeSO4•7H2O ha-1 was applied with or without H3PO3. Spray suspensions reduced the pH of the water carrier, therefore two additional growth chamber experiments were conducted to better understand the effects of these treatments on leaf surface pH and Microdochium patch suppression. The first growth chamber experiment determined that treatments reduced the leaf surface pH of annual bluegrass compared to the well water control and that 3.7 kg H3PO3 ha-1 combined with FeSO4•7H2O, regardless of the rate, produced the greatest reduction on leaf surface pH. The second growth chamber experiment determined that sulfuric acid (H2SO4) at a 0.5% spray solution rate was always in the group that produced the lowest annual bluegrass leaf surface pH, but did not suppress Microdochium patch, suggesting that leaf surface pH was not responsible for the suppression of Microdochium patch.