The “summah” season officially ends in September in the Northern Hemisphere. Although golf course turf maintenance still has a long to-do list, perhaps it’s time to plan ahead for winter and snow mold.
Pink snow mold is caused by the fungus Microdochium nivale and can affect all cool-season turfgrasses. It is especially damaging to putting greens. Pink, white or tan patches of blighted and matted turf is often observed during cold and wet environmental
conditions of late fall and winter. If the disease is associated with snow cover, it’s called pink snow mold; without snow cover, it’s Microdochium patch.
Golf course superintendents in Ireland and northern Europe consider Microdochium patch to be one of the most troublesome turf diseases to manage. While there are many superintendents smarter than a doctor, few possess an actual doctorate. At 52, John
Dempsey, Ph.D., started to pursue a baccalaureate degree, on his own time while maintaining his full-time position as a golf course superintendent in Ireland. He continued his studies, and at 59 earned a Ph.D. from the University of West England-Bristol.
Dempsey combined his 35 years’ experience as superintendent with his research skills to investigate the use of phosphite (PO3-3) for Microdochium patch control on putting greens in Ireland. Phosphite is derived from phosphorous acid (H3PO3). Phosphorous
acid is modified with potassium hydroxide (KOH) to form potassium phosphite in the form of dihydrogen phosphite (KH2PO3) or dipotassium hydrogen phosphite (K2HPO3).
Treatments were arranged in a randomized design typical for field experiments, with five replications per treatment. All treatments were applied every 14 days from September through March in 2010 and in 2011. All treatments were applied in 2 gallons of
water carrier per 1,000 square feet (800 liters per hectare).
The treatments were: (1) PK Plus (3N-7P2O5-18K2O; Grigg Bros.), which contained 14% KH2PO3 and applied at 1.1 pounds phosphite per 1,000 square feet (53.7 kilograms per hectare); (2) PK Plus + biostimulant (5N-0P2O5-3K2O; amino acids, micronutrients,
kelp); (3) iprodione fungicide at label use rate; (4) iprodione + PK Plus; (5) fertilizer (3N-7P2O5-18K2O); and (6) untreated. Of note, repeated applications of iprodione would be considered excessive and beyond label instructions but were applied
repeatedly in these field trials to ensure maximum disease suppression.
Combining data from both years, results on an annual bluegrass (Poa annua) putting green were: 35% plot area with visible snow mold in untreated or fertilizer-only plots; 15% in PK Plus or PK Plus + biostimulant plots; 5% in fungicide-only plots; and
<1% snow mold in plots treated with fungicide + PK Plus. Also combining data from both years, results on the velvet bentgrass (Agrostis canina) putting green were: 50% snow mold in untreated or fertilizer-only plots; 25% in PK Plus or PK Plus +
biostimulant plots; 5% in fungicide-only plots; and <2% snow mold in plots treated with fungicide + PK Plus.
Under severe Microdochium patch pressure at both putting green sites and years, plots treated with sequential applications of phosphite alone (as delivered from PK Plus) showed significant and consistent reduction in disease severity compared to fertilizer
alone or untreated plots. The biostimulant did not improve phosphite’s disease-suppression ability compared to applying phosphite alone. Although the fungicide-alone program provided good disease control, the combination of phosphite applied
with the fungicide provided the best control of Microdochium patch.
While it may be unrealistic to apply a fungicide every 14 days from September through March or in situations where fungicide use is not an option, these field studies showed repeated applications of a phosphite could reduce the severity of Microdochium
patch on putting greens. Dempsey’s research also indicates that phosphite has a complex mode or mechanism of action, both directly on the snow mold pathogen and indirectly by stimulating a defense response within the turfgrass plant.
Dempsey is the turfgrass industry’s leading authority on phosphites. Now a retired greenkeeper, he can spend more time with his second career of conducting research and attending turf conferences with his wife, Mary.
Source: Dempsey, J.J., I.D. Wilson, P.T. Spencer-Phillips and D.L. Arnold. 2012. Suppression of Microdochium nivale by potassium phosphite in cool-season turfgrasses. Acta Agriculturae Scandinavica, Section B – Soil and Plant Science, 62:sup1, 70-78
(https://doi.org/10.1080/09064710.2012.681392).
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 20-year member of GCSAA.