Cracking the Code on Turfgrass's Most Persistent Foe
How cutting-edge research is revolutionizing dollar spot control through precise fungicide timing and application techniques
Imagine a pristine emerald-green golf course, a carpet of perfect grass stretching to the horizon. Now, imagine it blighted by small, straw-colored patches that slowly merge into unsightly scars. This isn't just a bad mowing job; it's the work of a formidable adversary: dollar spot. For turf managers, this fungal disease is a perennial nightmare, draining resources and blemishing perfect turf.
But what if we could stop this invader in its tracks, not with more chemicals, but with smarter science? Recent research is zeroing in on a critical window of opportunity, revealing that how and when we fight back can be just as important as the weapon we choose.
Dollar spot is caused by the fungus Clarireedia homoeocarpa. It doesn't kill the entire plant; instead, it attacks the blades of grass, leaving behind those characteristic bleached-tan lesions with a distinctive reddish-brown border.
The fungus thrives in moderate temperatures (60-80°F or 15-27°C) and high humidity, often making spring and fall its prime seasons.
A severe infection weakens the turf, making it susceptible to other stresses like drought, heat, and invasion by weeds.
For years, the standard protocol has been to apply fungicides preventatively, before the disease even appears. But what if you miss that window? A groundbreaking study set out to answer two crucial questions for curative control (applying fungicide after the first signs of disease):
Researchers designed a meticulous experiment on plots of creeping bentgrass, a grass famous for its use on golf course putting greens.
Multiple small plots were established and allowed to become naturally infected with the dollar spot fungus.
Scientists waited until the first dollar spot symptoms appeared, marking "Day 0" for the experiment.
Spray Volume: The same fungicide (a common combination of boscalid and pyraclostrobin) was applied at different volumes of water per acre: a low volume of 2 gallons, a medium volume of 30 gallons, and a high volume of 70 gallons.
Application Timing: Applications were made at different intervals after the first symptoms were seen: immediately (0 days), 1 day later, 2 days later, and 3 days later. An untreated control plot received no fungicide.
Researchers then counted the number of dollar spot infection centers in each plot over the following weeks to determine which combination was most effective at halting the disease's progress.
The results were striking, highlighting a clear winner and a rapidly closing window of opportunity.
The core finding was that spray volume had a massive impact on curative success, but only if applied almost immediately.
Consistently superior, providing effective control even when applied 1 or 2 days after symptom appearance.
Only effective when applied on the very same day symptoms were first observed. Waiting just 24 hours rendered it nearly useless.
Offered a middle ground, but was still outperformed by the high-volume application.
It's all about coverage. A higher volume of water acts like a better delivery truck, ensuring every single blade of grass is thoroughly drenched and the fungicide reaches the base of the plant where the fungus is active. A low volume might only hit the top of the canopy, leaving the crucial lower areas unprotected.
| Application Timing (Days after symptoms) | Low Volume (2 gal/acre) | Medium Volume (30 gal/acre) | High Volume (70 gal/acre) |
|---|---|---|---|
| 0 | 95% | 98% | 99% |
| 1 | 40% | 85% | 96% |
| 2 | 15% | 65% | 90% |
| 3 | 10% | 45% | 70% |
| Treatment Group | Day 0 (First Symptoms) | Day 7 | Day 14 |
|---|---|---|---|
| Untreated Control | 5 | 105 | 280 |
| High Volume, Day 0 | 5 | 8 | 10 |
| High Volume, Day 2 | 5 (at app) | 25 | 45 |
| Low Volume, Day 0 | 5 | 15 | 22 |
| Low Volume, Day 2 | 5 (at app) | 80 | 210 |
| Tool / Reagent | Function in the Fight |
|---|---|
| Creeping Bentgrass | The model organism; a high-value turfgrass notoriously susceptible to dollar spot, making it perfect for testing control strategies. |
| Boscalid | A systemic fungicide that inhibits fungal respiration. It's absorbed by the plant and travels to the site of infection. |
| Pyraclostrobin | A broad-spectrum fungicide from the Qol (strobilurin) group. It disrupts energy production in the fungus. |
| Surfactant | A "wetting agent" added to the spray tank to help the solution spread evenly and stick to waxy grass blades, improving coverage. |
| Track Sprayer | A precise, automated laboratory sprayer that ensures every plot receives the exact same amount of chemical, eliminating human error. |
So, what does this all mean for the fight against dollar spot? The take-home message is a powerful one-two punch:
For curative applications, a high spray volume (e.g., 70 gallons/acre) is non-negotiable. It provides a robust safety net, ensuring the fungicide penetrates the dense turf canopy and reaches the enemy.
The concept of "curative" is incredibly narrow. The clock starts ticking the moment the first silver dollar-sized patch appears. Delaying application by even a day can mean the difference between total control and significant turf damage.
This research shifts the paradigm from simply "what chemical to use" to a more sophisticated strategy of "how to deliver it and when to strike." By adopting this science-backed approach, turf managers can protect our green spaces more effectively, efficiently, and with greater confidence than ever before. The war on dollar spot isn't over, but we've just been handed a much better battle plan.