Managing fungal diseases in lawns effectively requires a combination of preventive practices, timely treatment, and rotating fungicide classes to prevent resistance buildup. Here’s a complete guide:
1. Proper Diagnosis
Start by identifying the type of fungus (e.g., brown patch, dollar spot, rust, pythium, etc.). Misdiagnosing can lead to using the wrong product.
- Brown Patch – Often appears as large, circular brown areas.
- Dollar Spot – Small, silver-dollar-sized patches.
- Pythium Blight – Greasy, matted turf, especially in high humidity.
You can send samples to a local extension service or turf lab for confirmation.
2. Cultural Controls (Prevention & Management)
Before applying chemicals, make sure cultural practices support a healthy lawn:
- Water early in the morning to let grass dry during the day. Avoid late afternoon/evening watering.
- Improve air circulation (prune trees/shrubs and don’t mow too short).
- Use nitrogen correctly – Avoid high-nitrogen fertilizer in hot, humid months.
- Remove thatch if it’s over ½ inch thick.
3. Fungicide Application
Once a fungal issue is confirmed:
A. Choose the Right Fungicide Class
Fungicides are grouped into FRAC (Fungicide Resistance Action Committee) codes. Some common ones for lawns:
- Group 3 – DMI (e.g., propiconazole)
- Group 1 – Benzimidazoles (e.g., thiophanate-methyl)
- Group 7 or 11 – SDHIs (e.g., fluopyram) and QoIs (e.g., azoxystrobin)
Select a product labeled for the fungus you’re treating and your grass type.
B. Application Tips
- Apply when conditions are conducive to fungal growth (warmth + humidity).
- Use adequate water volume to ensure even coverage and penetration.
- Avoid mowing for 24 hours before/after application if possible.
- For prevention, apply ahead of forecasted high humidity/rain.
Fungicide Rotation Guidelines
Why Rotate?
Repeated use of the same class can lead to fungicide resistance, making treatments ineffective over time.
How Often Should You Rotate?
- Rotate fungicides with different FRAC codes every 2–3 weeks or every application, especially if multiple treatments are needed in a season.
- Avoid using the same class more than 2 times consecutively in a single season.
Sample Rotation Schedule:
| Week | Product | FRAC Group |
|---|---|---|
| 1 | Propiconazole | 3 |
| 3 | Azoxystrobin | 11 |
| 5 | Thiophanate-methyl | 1 |
| 7 | Fluopyram | 7 |
Bonus: Bio-fungicides & Organic Options
If you’re aiming for a low-impact or organic approach, consider:
- Bacillus subtilis (e.g., Serenade) – a microbial biofungicide.
- Compost teas – can improve microbial diversity and reduce fungal outbreaks.
- Neem oil – useful against surface-level fungi.
Summary
| Strategy | Details |
|---|---|
| Diagnosis | Confirm the type of fungus to treat accurately. |
| Prevention | Improve watering, mowing, and airflow. |
| Fungicide Use | Use targeted fungicides and apply correctly. |
| Rotation | Alternate fungicides with different FRAC codes every 2–3 weeks. |
