Dollar spot can remain active - or resurge - in late fall when mild temperatures, high humidity, and prolonged leaf wetness persist. Late-season outbreaks can be particularly problematic because turf growth and recovery slow as temperatures decline, allowing symptoms to persist through winter and potentially affect spring appearance.
Why Does Dollar Spot Resurge in Late Fall?
Several factors may contribute to late-fall resurgence:
- Prolonged dew and leaf wetness: Cooler nights promote heavy dew, which can remain on the leaf surface well into the morning and provide favorable conditions for infection.
- Mild temperatures and high humidity: Short periods of mild temperatures combined with high relative humidity can trigger renewed disease activity, even after disease pressure has declined earlier in the fall.
- Reduced turf growth and recovery: As temperatures decline, turf growth slows, reducing the plant’s ability to recover from infection and grow through dollar spot symptoms.
- Existing pathogen inoculum: Dollar spot pathogens can persist in the turf canopy and thatch and rapidly resume activity when environmental conditions again become favorable.
- Gaps in fungicide protection: Extending spray intervals or ending applications too early can allow disease to re-establish if favorable conditions persist or return.
- Potential fungicide-related disease enhancement: The causes of fall dollar spot resurgence are not fully understood. Fungicides may alter the turf microbial community, including microorganisms that naturally antagonize the dollar spot pathogen, potentially contributing to disease rebound after fungicide protection ends. Recent observations of aggressive, mycelium-producing dollar spot populations in the Northeast also raise the possibility that differences among Clarireedia species or strains, including fungicide sensitivity, may contribute to fall resurgence.
Management Considerations
- Monitor disease pressure: Use predictive tools such as the Smith-Kerns dollar spot model in combination with weather conditions and field observations.
- Maintain balanced fertility: Avoid nitrogen deficiency and other forms of turf stress that can increase dollar spot susceptibility.
- Reduce leaf wetness: Remove dew when practical and improve air movement and drainage to promote more rapid drying of the canopy.
- Continue appropriate cultural practices: Aeration, topdressing, and other practices that promote healthy turf and improve the growing environment can support disease management.
- Do not rely solely on the calendar: If environmental conditions remain favorable for dollar spot, consider maintaining fungicide protection rather than ending applications simply because it is late in the season.
Manage established outbreaks aggressively: Once dollar spot is established, curative control can be difficult, particularly when fungicide resistance or reduced sensitivity is present. Where permitted by the label, combining fungicides with different modes of action may improve control. Contact/multi-site fungicides such as chlorothalonil or fluazinam, used in combination with an effective fungicide from a different FRAC group, such as a QoI (e.g., fluoxastrobin or mandestrobin), may provide useful control when the pathogen population is sensitive to the selected chemistries. Fungicide selection should be guided by known or suspected resistance; avoid relying on DMIs or SDHIs where resistance is prevalent.
Prioritize prevention: Preventive fungicide applications are generally more effective than attempting to control well-established outbreaks. Use effective protectant and/or multi-site fungicides when disease risk is high, while rotating modes of action to manage resistance. Always follow product labels and local recommendations.
Bottom Line
Late fall does not necessarily mean the end of dollar spot. Continue monitoring weather and disease pressure, minimize leaf wetness and turf stress, and maintain an appropriate disease-management program while conditions remain favorable for infection. Preventing a late-season outbreak is generally easier than trying to control an established outbreak as turf growth slows.
Finish the season strong - don't let late-fall dollar spot become a spring problem.
Submitted by: Dr. Geunhwa Jung