The Dollar Spot vs. Soil Diversity
- David Santos, MBiotech
- May 7
- 3 min read
By David Santos, MBiotech
30-second Summary
Dollar spot pressure is not only about pathogen presence and weather; rhizosphere structure and local soil chemistry may also shape disease development.
Higher microbial diversity does not automatically mean stronger suppression.
Community structure, niche occupation, and soil iron may matter more than a simple species count.
Plants can influence microbiome assembly through root exudates, although that evidence comes from model systems rather than turf-specific field work.
For superintendents, breakthrough disease may indicate a stressed or less stable root-zone ecosystem, not just a failed fungicide program.
Somewhere in a Wisconsin bentgrass trial, a research team found something that didn't add up. Plots with greater dollar spot pressure had greater microbial diversity, not less.[1]
That result came from the Koch Lab at the University of Wisconsin-Madison and was published in 2021.[1] Their study examined how rhizosphere microbial communities differ among bentgrass plots with varying dollar spot susceptibility and what these differences might mean for disease development.
The Diversity Paradox
A 2021 study from the University of Wisconsin–Madison's Koch Lab, published in Applied and Environmental Microbiology, challenged the assumption that higher microbial diversity always tracks with lower dollar spot pressure. In that study, rhizosphere samples associated with higher dollar spot susceptibility exhibited higher alpha diversity than those associated with moderate susceptibility.[1]
That does not mean diversity is unimportant. It means diversity alone is not the only indicator of disease suppression. The same study also found that rhizosphere community composition, co-occurrence patterns, and hyperlocal variation in soil iron were associated with differences in dollar spot development.[1]
Explore the research. Want to go deeper on turf microbiology and rhizosphere function? Visit En‑Turf's Resources for research summaries, or read The Science: How Microbials Work to Mitigate Drought & Salinity Stress in Turfgrass for a practical overview.
Niche Space and Suppression
This shifts the conversation from "how many microbes are there?" to "which functional groups are established, and how stable is the community around the root?" In ecological terms, disease suppression may depend in part on niche occupation: when space, nutrients, and interaction networks are already occupied by established microbes, pathogen success can become more difficult.[1][2]
A useful mechanistic example comes from a 2019 Science paper from researchers at NIOO-KNAW, which showed that pathogen pressure can trigger recruitment of disease-suppressive functions in the root microbiome. In that system, taxa including Chitinophagaceae and Flavobacteriaceae were enriched, alongside functions associated with chitin degradation and antifungal metabolite production.[2]
That study was not conducted in turfgrass, so it should be treated as a conceptual parallel rather than direct evidence for dollar spot management. Still, it supports the broader idea that suppression is not only about killing a pathogen outright but also about reorganizing the microbial community in ways that reduce the pathogen's opportunity.[2]
The Plant's Role
The plant itself is also part of this process. Research published in PNAS in 2018 showed that Arabidopsis can exude coumarins through its roots in ways that shape microbiome assembly, particularly under iron-deficiency signalling controlled by MYB72-dependent pathways.[3]
Here again, the leap to turf management should be framed carefully. This paper does not show that creeping bentgrass under traffic stress or low mowing height recruits the same microbes in the same way, but it does strengthen the broader principle that plant metabolites can help determine which microbes are favoured in the rhizosphere.[3]
Management Perspective
For superintendents, this body of research offers a different lens on disease pressure. When dollar spot breaks through a program, it may reflect not only favourable weather and pathogen activity, but also a rhizosphere community that is less stable, less suppressive, or less supported by local soil chemistry.
That perspective does not replace fungicides, forecasting, or sound agronomy. It suggests that resilience may also depend on supporting the biological structure around the root zone, especially when environmental stress, nutrient imbalance, or other site-specific factors reduce the plant's ability to maintain a favourable microbial community.
The open question is how to measure those structural traits reliably in the field. If alpha-diversity is not enough on its own, then future turf diagnostics may need to look more closely at microbial composition, functional potential, and local drivers to better understand what makes one stand more resilient than another.
References
[1] Chou et al. (2021). Hyperlocal Variation in Soil Iron and the Rhizosphere Bacterial Community Determines Dollar Spot Development in Amenity Turfgrass. Applied and Environmental Microbiology. Koch Lab, University of Wisconsin–Madison. https://journals.asm.org/doi/10.1128/AEM.00149-21
[2] Carrión et al. (2019). Pathogen-induced activation of disease-suppressive functions in the endophytic root microbiome. Science. NIOO-KNAW. https://www.science.org/doi/10.1126/science.aaw9285
[3] Stringlis et al. (2018). MYB72-dependent coumarin exudation shapes root microbiome assembly to promote plant health. PNAS. Utrecht University. https://www.pnas.org/doi/10.1073/pnas.1722335115
