ALTERING LEAF PH TO SUPPRESS DOLLAR SPOT IN AMENITY TURFGRASS

Abstract

Due to its high adaptability to novel stressors and variable environmental conditions, managing Clarireedia jacksonii, the causal agent of dollar spot disease, continues to pose a major challenge in turfgrass systems. Conventional control methods are increasingly constrained by limited chemical options, rising concerns over pesticide resistance, and inconsistent efficacy of biological products. As a result, there is a growing demand for non-conventional approaches to disease management. This field-based study evaluated the potential of foliar-applied alkaline substances to suppress dollar spot on a mixed stand of creeping bentgrass (Agrostis stolonifera L.) and annual bluegrass (Poa annua L.) over two consecutive growing seasons (2023–2024). Treatments varied by chemical identity, rate, application frequency, spray volume, and their

resulting foliar alkalinity, quantified as kilograms of CaCO₃-equivalent per hectare. Results demonstrated that disease suppression was strongly associated with surpassing a threshold level of foliar alkalinity, rather than the specific compound or nominal application rate. Across both years, treatments delivering >30 kg per ha CaCO₃-equivalent consistently reduced disease severity by over 85%, with weekly applications of potassium bicarbonate achieving suppression levels of up to 98%. Elevated foliar pH (>8.9) was a strong predictor of reduced disease development. While spray volume had minimal impact on outcomes, frequent reapplication proved critical to maintaining alkaline conditions on the phylloplane. However, high-alkalinity treatments also introduced phytotoxic effects, particularly under short reapplication intervals, resulting in reduced turf quality. This highlights a key trade-off between effective disease suppression and aesthetic turf performance. Although additional multi-year research and microbiological diagnostics are necessary to evaluate long-term sustainability, the present study offers strong field-based evidence supporting foliar alkalinity modulation as a viable non-conventional approach to dollar spot management. Current findings emphasize the importance of aligning product selection with site- specific goals, particularly in high-stakes turf systems. Future research into microbial interactions and physiological responses may further optimize these treatment strategies.