High Nitrogen Fertilization Suppresses Dollar Spot in Amenity Turfgrass Through Promoting Oxalic Acid-Degrading Bacteria

High nitrogen (N) fertilization can suppress dollar spot (<i>Clarireedia</i> spp.) disease of amenity turfgrass. However, golf course superintendents avoid high N fertilization due to the reduced playability of putting greens and concerns over increased cost and environmental contamination issues. Understanding how N fertilization suppresses dollar spot could result in novel control strategies that do not rely on high N fertilization or repeated pesticide applications. In 2017, we sampled a previous 3-year study conducted in Madison, WI, on turfgrass treated with either 0, 4.9, or 29.3 kg N/ha/year. Dollar spot was assessed every 2 weeks during the study period, and microbiome samples were collected from each plot at five different time points during 2017. The bacterial 16S rRNA gene and fungal internal transcribed spacer region were sequenced using high-throughput sequencing, and the <i>frc</i> gene copy number was quantified using droplet digital PCR. The <i>frc</i> gene was previously established as a biomarker for oxalic acid-degrading bacteria. The 29.3 kg N/ha treatment reduced disease severity and had higher <i>frc</i> gene expression than lower N rates. Prokaryotic alpha diversity significantly declined under 29.3 kg N/ha, whereas fungal diversity remained relatively stable. N treatment significantly affected prokaryotic beta diversity but not fungal diversity. The results suggest that N may have a role in selecting microbes that degrade oxalic acid, an important virulence factor of <i>C. jacksonii</i>. Identifying the specific organisms involved in oxalic acid degradation may result in new biocontrol strategies and improve the sustainable management of dollar spot. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.