Application of alkaline products increases phylloplane pH and suppresses dollar spot on creeping bentgrass

Dollar spot, caused by Clarireedia spp., is one of the most destructive diseases of amenity turfgrass worldwide and is increasingly difficult to manage due to fungicide resistance, regulatory constraints, and limited alternative control options. Manipulation of phylloplane surface pH has been used in some crops as a non-conventional disease management strategy, but its efficacy and practical limitations in turfgrass systems are poorly understood. Field experiments were conducted in Madison, WI, USA, during the 2023 and 2024 growing seasons to evaluate whether repeated applications of alkaline compounds could suppress dollar spot and to optimize application strategies for turfgrass managers. Treatments delivering ≥30 kg ha⁻¹ CaCO₃-equivalent alkalinity consistently suppressed dollar spot by >90% relative to non-treated controls, whereas acidic and pH-neutral treatments provided little to no disease control. Dollar spot severity was negatively correlated with both phylloplane pH (R² = 0.76) and treatment alkalinity (R² = 0.90), with marked disease reductions occurring at phylloplane pH values near 9. Weekly reapplications provided the most consistent disease suppression but also increased the risk of short-term phytotoxicity, highlighting a trade-off between efficacy and turf aesthetics. These results demonstrate that application of alkaline products can effectively suppress dollar spot and represents a promising alternative disease management strategy, although mitigation of phytotoxicity will be critical for broader adoption in amenity turfgrass systems.