Optimizing liquid‐applied iron sulfate rate and application interval for dollar spot suppression on golf course fairways

Iron sulfate applications reduce dollar spot severity on golf course turfgrass, but further optimizing the use of iron sulfate may increase efficacy and encourage more widespread adoption by golf course superintendents. Three iron sulfate rates (9, 18, 36 kg ha −1 ), two application intervals (7 and 14 days), three water volumes (306, 612, and 1223 L ha −1 ), and combinations with fertilizer and fungicide products were evaluated at field locations in Madison, WI, Bloomington, MN, and Blacksburg, VA, in 2018 and 2019. Iron sulfate rate decreased dollar spot at all locations in a dose‐dependent manner, and 7‐day applications were more efficacious than 14‐day applications. Water volume had no impact on disease severity at any location and combining iron sulfate with fertilizer had minimal impact as well. These results demonstrate improved iron sulfate strategies for dollar spot management and can be implemented by golf course superintendents in areas where fungicide resistance and fungicide regulations limit the use of traditional fungicides. Iron sulfate suppresses dollar spot in a dose‐dependent manner. Phytotoxicity occurrence increased at the 36 kg ha −1 rate of iron sulfate. Shorter reapplication intervals improved dollar spot suppression without increasing phytotoxicity. Other factors, such as spray water volume and combining with urea, had minimal influences on the efficacy of iron sulfate against dollar spot. Dollar spot is a severe disease affecting amenity turfgrass, and fungicide alternatives are needed to lower costs and manage fungicide resistant fungi. Past research has shown that iron sulfate can suppress dollar spot development, but little is known about the most effective iron sulfate rate, reapplication interval, and water volume for dollar spot control. Our study was conducted in 2018 and 2019 in WI, MN, and VA. Iron sulfate suppressed dollar spot in a dose‐dependent manner and reapplications every 7 day were more effective than reapplications every 14 day. No consistent impact of water volume on disease control was observed at any location. In addition, combining iron sulfate with other products like urea fertilizer did not improve disease control compared to iron sulfate applied alone. The results from this study provide important information for golf course superintendents looking to implement iron sulfate usage at their golf course.