Scientists Hunt for a Cure for Dollar Spot
By Turfgrass Research Team | Published: October 2023
You've seen the damage: those small, straw-colored patches that slowly merge into a blight on an otherwise perfect green lawn. This is dollar spot, a notorious disease that plagues golf courses, sports fields, and home lawns alike . For decades, superintendents have fought this foe with fungicides, but the enemy is evolving, developing resistance . Now, a new scientific breakthrough has redefined the battleground, and researchers are racing to find a new generation of sustainable solutions.
This article delves into the exciting world of turfgrass pathology, where scientists are testing both nature's own assassins—biological control agents—and next-generation synthetic fungicides in a high-stakes battle against a newly defined enemy: Clarireedia jacksonii sp. nov.
Human-made chemicals designed to inhibit or kill the fungus. Effective but can lead to resistance.
Living organisms that combat the pathogen through competition, predation, or immune stimulation.
For years, the fungus causing dollar spot was known as Sclerotinia homoeocarpa. But recent advances in genetic analysis revealed a case of mistaken identity . Scientists discovered that the turfgrass pathogen was distinct enough to deserve its own genus and species name: Clarireedia jacksonii.
Why does a name change matter? It's like discovering a cold-causing virus you've been studying is actually a completely different family of viruses. This reclassification allows for more precise research. By correctly identifying the target, scientists can now develop more accurate diagnostic tools and tailor control methods specifically for C. jacksonii, making the fight more efficient and effective .
Former Name: Sclerotinia homoeocarpa
Disease Caused: Dollar Spot
Primary Hosts: Turfgrasses
Optimal Temperature: 20-25°C
Key Symptom: Straw-colored patches
Identification: Genetic analysis
The core of modern plant disease management involves a two-pronged strategy evaluating both synthetic fungicides and biological control agents (BCAs). Researchers evaluate these strategies through a two-phase process :
Testing potential controls in petri dishes to see if they directly affect the fungus in controlled conditions.
Applying promising candidates to turfgrass in real-world conditions before disease strikes to assess protection.
Scientists prepare Petri dishes filled with a nutrient-rich gel called PDA (Potato Dextrose Agar). This provides a standardized food source for the fungus.
A small plug of agar, taken from a pure, growing culture of C. jacksonii, is placed in the center of each dish.
For BCAs, a plug of a beneficial fungus or bacteria is placed near the pathogen. For synthetic fungicides, a paper disc soaked in the chemical is placed nearby.
The dishes are sealed and placed in an incubator. Researchers measure the growth of C. jacksonii over several days.
| Item | Function |
|---|---|
| Potato Dextrose Agar (PDA) | The standard nutrient medium used to culture and grow Clarireedia jacksonii in the lab. |
| Mycelial Plug | A small, uniform disc taken from a growing fungal colony to transfer the pathogen. |
| Incubator | Temperature-controlled chamber maintaining ideal environment for consistent fungal growth. |
| Beneficial Microbes | Live cultures of BCAs like Trichoderma spp. or Bacillus spp. used to combat the pathogen. |
| Technical Grade Fungicides | Pure, concentrated forms of synthetic chemicals used for precise testing. |
| Disease Rating Scale | Standardized visual scale to assess turfgrass area affected by dollar spot. |
The key measurement is the growth radius of the C. jacksonii colony. Success is determined by how much a treatment inhibits this growth compared to the control .
| Treatment Type | Specific Agent | Average Growth Radius of C. jacksonii (mm) | % Inhibition vs. Control |
|---|---|---|---|
| Control (No Treatment) | --- | 45.0 | 0% |
| Synthetic Fungicide | Fluazinam | 0.0 | 100% |
| Synthetic Fungicide | Propiconazole | 12.5 | 72.2% |
| Biological Control | Trichoderma harzianum | 15.0 | 66.7% |
| Biological Control | Bacillus subtilis | 28.0 | 37.8% |
Analysis: In this sample data, the synthetic fungicide Fluazinam was completely effective in the lab. The BCA Trichoderma harzianum also showed strong inhibition, nearly matching the performance of Propiconazole. This makes it a prime candidate for the next stage: field trials.
The most promising candidates from the in vitro trials are then moved to controlled field plots of creeping bentgrass or annual bluegrass .
| Treatment Type | Specific Agent | Average Disease Severity (%) | Efficacy vs. Control |
|---|---|---|---|
| Untreated Control | --- | 45% | --- |
| Synthetic Standard | Propiconazole | 8% | 82.2% |
| Biological Control | Trichoderma harzianum | 18% | 60.0% |
| Biological Control | Bacillus subtilis | 35% | 22.2% |
Analysis: Here, the field results tell a more nuanced story. While Trichoderma was not as effective as the synthetic standard, its 60% efficacy is commercially very significant. It shows that this BCA can provide substantial protection in a real-world environment. Bacillus subtilis, which showed some promise in the lab, was much less effective in the field, highlighting why this two-phase testing process is so critical .
The war on dollar spot is entering a new, more sophisticated era. The reclassification to Clarireedia jacksonii has given scientists a clearer target . The research pipeline, moving from in vitro lab screens to preventative field evaluations, is efficiently identifying the next generation of control agents.
The most promising future lies not in choosing between biological and synthetic options, but in integrating them.
A turf manager might use a robust BCA like Trichoderma as a foundational program, only bringing in a synthetic fungicide as a "rescue" treatment during severe disease pressure. This approach, known as Integrated Pest Management (IPM), prolongs the effectiveness of fungicides, reduces environmental impact, and creates a more resilient, healthy lawn for everyone to enjoy . The silent battle continues, but the arsenal is getting smarter and more sustainable.