Lawn fungicides play a crucial role in preventing and treating fungal diseases that can damage cool-season lawns. If left untreated, fungal infections can quickly spread, leaving your yard with unsightly patches and weakened grass.
Choosing the right fungicide and applying it at the right time can make all the difference in maintaining a healthy lawn.
Lawn fungicides help control fungal diseases like brown patch, dollar spot, and red thread. Apply a preventative fungicide in late spring or early summer, and use curative fungicides at the first sign of disease. Options like Scott’s DiseaseEx, BioAdvanced Fungus Control, and Heritage G are highly effective.
What Are Lawn Fungicides?
Lawn fungicides are treatments designed to prevent and control fungal diseases that can damage your grass. These products work by either stopping fungal spores from spreading (preventative fungicides) or eliminating existing fungus before it spreads further (curative fungicides).
Fungicides come in two main types:
- Preventative fungicides – Applied before a fungal outbreak occurs, creating a protective barrier to stop spores from infecting the grass. These are best used in late spring or early summer when conditions favor fungal growth.
- Curative fungicides – Used after a fungal infection appears, helping to slow or eliminate the disease. While effective, curative treatments work best when applied early in the infection stage.
Using fungicides properly can save your lawn from severe damage and keep it looking healthy year-round. But timing and application methods matter-using them too late or incorrectly may not work.
In the next sections, we’ll break down the best fungicides for different lawn diseases and when to use them.
Common Lawn Fungal Diseases in Cool-Season Lawns
Lawn fungus can be sneaky. One day, your grass looks lush and green, and the next, you’re seeing weird patches, discolored spots, or fuzzy coatings on your lawn. If that sounds familiar, you’re probably dealing with one of these common fungal diseases.
1. Brown Patch
Ever wake up to huge brown circles on your lawn? That’s Brown Patch doing its thing. This one loves hot, humid weather, especially when nighttime temperatures stay above 60°F. If your grass looks like it has big, irregular dead patches with a dark ring around the edges, Brown Patch is likely the culprit.
- Caused by: Overwatering, high humidity, and mowing too short.
- Treatment: Cut back on evening watering, keep your mower blades sharp, and apply Scott’s DiseaseEx or BioAdvanced Fungus Control for quick results.
2. Dollar Spot
This one starts small-literally. You’ll see tiny, round brown patches, usually about the size of a silver dollar (hence the name). But don’t ignore it-if left untreated, these spots spread and merge, turning large sections of your lawn dry and brown. Dollar Spot usually pops up when your lawn isn’t getting enough nitrogen and humidity levels are high.
- Caused by: Low nitrogen levels, humid weather, and excessive thatch.
- Treatment: Feed your lawn with a nitrogen-rich fertilizer, mow at the right height, and apply a fungicide like Heritage G or Eagle 20EW.
3. Red Thread
If your grass looks like it has been sprinkled with pink or red threads, you’re probably dealing with Red Thread. It’s not as destructive as Brown Patch, but it sure doesn’t look great. This one is mostly a cosmetic issue, meaning your grass will recover on its own if you improve your lawn’s health.
- Caused by: Cool, damp weather and low nitrogen levels.
- Treatment: Fertilize your lawn with a slow-release nitrogen product, improve air circulation, and consider a preventative fungicide if the problem keeps coming back.
4. Snow Mold (Gray & Pink)
Ever notice white or pink fuzzy patches on your lawn as the snow melts in spring? That’s Snow Mold, a fungus that thrives under a thick snow cover. It’s especially common in yards where the grass was left too long before winter. While Snow Mold usually clears up on its own, it can leave your lawn looking rough for weeks.
- Caused by: Snow trapping moisture, poor drainage, and leaving grass too long before winter.
- Treatment: Rake the affected areas to break up the mold, improve drainage, and apply a fall fungicide to prevent it next winter.
5. Pythium Blight
Pythium Blight is the worst of the worst. This fungus doesn’t just kill grass-it destroys it fast. If you notice greasy, water-soaked patches that quickly turn brown and spread, act immediately. This one thrives in hot, wet conditions and spreads like wildfire if your lawn is holding too much moisture.
- Caused by: Overwatering, poor drainage, and hot, humid weather.
- Treatment: Stop watering so much, improve lawn drainage, and apply a strong fungicide like Pillar SC to stop it in its tracks.
For more details on identifying and treating fungal diseases, check out How to Prevent and Treat Lawn Fungus in Cool-Season Lawns.
How Fungicides Work & When to Use Them
Fungicides are designed to prevent and treat fungal diseases by stopping spores from spreading and attacking grass. They come in two types:
- Preventative Fungicides: Applied before fungus appears to protect grass from infections.
- Curative Fungicides: Used after signs of disease appear to stop the spread and help the grass recover.
If you notice brown patches, discolored rings, or slimy grass, it’s time to act quickly. Applying a fungicide at the first sign of fungus can prevent long-term damage.
Lawn diseases like Brown Patch, Dollar Spot, and Red Thread are common in cool-season lawns, and treating them early prevents widespread damage.
Types of Lawn Fungicides
Understanding the difference between contact and systemic fungicides will help you choose the right product for your lawn’s needs.
Contact Fungicides
- Work by coating the grass blades to protect against infection.
- Must be reapplied frequently (every 7-14 days) since they wash away with rain or watering.
- Best for preventative use.
Systemic Fungicides
- Absorbed into the grass and move through the plant.
- Offer longer-lasting protection (2-4 weeks per application).
- Can treat existing fungal infections and prevent new ones.
Best Lawn Fungicides for Common Lawn Diseases
Different fungi require different treatments. Here are some of the best fungicides for common lawn diseases in cool-season lawns:
| Fungicide | Best For | Application Frequency |
|---|---|---|
| Scott’s DiseaseEx | Brown Patch, Dollar Spot | Every 2-4 weeks |
| BioAdvanced Fungus Control | Preventative & Treatment | Monthly |
| Bonide Infuse | Long-term protection | Every 4 weeks |
| Propiconazole (Liquid & Granular) | Red Thread, Snow Mold | Every 3-4 weeks |
| Heritage G Fungicide | Broad-spectrum disease control | Every 3-4 weeks |
| Headway G | Wide range of fungal infections | Every 2-4 weeks |
| Pillar SC | Fast-acting liquid fungicide | Monthly |
| Caravan G | Granular, long-lasting protection | Every 3-4 weeks |
These products are widely available at Amazon, home improvement stores, and local garden centers.
How to Apply Fungicides for Effective Results
Applying fungicide correctly ensures your lawn gets the best protection. Follow these steps for the best results:
- Read the Label – Always follow the manufacturer’s instructions for application rates and frequency.
- Apply in Dry Conditions – Fungicides work best when applied on a dry lawn with no rain expected for 24 hours.
- Use a Spreader or Sprayer – Granular fungicides need a broadcast spreader, while liquid fungicides should be applied with a sprayer.
- Water It In (If Required) – Some systemic fungicides need watering to absorb into the roots, while contact fungicides should stay on the blades.
- Reapply as Needed – Check the label for reapplication timing (usually every 2-4 weeks).
Preventative vs. Curative Fungicides
| Type of Fungicide | Application Timing | Effectiveness |
|---|---|---|
| Preventative Fungicides | Before fungal outbreaks | Highly effective in preventing lawn diseases |
| Curative Fungicides | After infection is visible | Stops further spread but may not fully restore grass |
Preventative fungicides work best when applied before peak fungus season-usually in late spring or early summer when humidity rises.
Curative fungicides help stop disease progression but won’t fully heal damaged grass. Combining both treatments can provide the best protection.
For additional lawn health strategies, including ways to improve soil drainage and reduce fungal risks, see When to Aerate and Dethatch Your Lawn.
Natural Alternatives to Fungicides
If you prefer a more natural approach, there are organic options that can help prevent and manage lawn fungus:
Neem Oil
- A natural fungicide that stops fungal spores from spreading.
- Safe for lawns, plants, and pets.
Baking Soda Spray
- Creates an alkaline environment that fungus can’t survive in.
- Mix 1 tablespoon of baking soda per gallon of water and spray affected areas.
Compost Tea
- Boosts beneficial microbes in the soil, which helps fight off fungal infections.
- Apply every 2-3 weeks for long-term protection.
Mistakes to Avoid When Using Fungicides
- Applying Too Late – Once a fungal infection spreads too far, fungicides won’t be as effective.
- Overusing Fungicides – Using fungicides too often can lead to fungal resistance, making treatment less effective.
- Not Rotating Products – Switching between different fungicides (with different active ingredients) helps prevent resistance.
- Ignoring Lawn Health – Fungicides work best when paired with proper mowing, watering, and aeration.
Safety Precautions & Environmental Considerations
Fungicides contain chemicals that can affect your lawn’s ecosystem. Always wear gloves, protective clothing, and a mask when applying them. Also:
- Avoid spraying near water sources to prevent runoff.
- Apply in low wind conditions to reduce chemical drift.
- Follow the recommended waiting period before allowing pets or children onto treated grass.
Seasonal Fungicide Application Guide
| Season | Fungicide Application Tips |
|---|---|
| Spring | Apply a preventative fungicide before peak fungal growth. |
| Summer | Monitor humidity levels and reapply as needed. Use systemic fungicides for active infections. |
| Fall | Use contact fungicides to prevent fall fungal outbreaks like Snow Mold |
| Winter | Avoid applications unless dealing with winter-active diseases like Snow Mold. |
Final Thoughts
Fungicides can be a game-changer when dealing with lawn fungus, but they work best as part of a balanced lawn care routine. Keeping your lawn healthy, properly watered, and aerated reduces the chances of fungal outbreaks in the first place.
If you’re already battling lawn fungus, choosing the right fungicide and applying it correctly will help get your yard back on track. Whether you prefer chemical solutions or natural alternatives, having a plan in place will keep your cool-season lawn looking great all year long.
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Hi, I’m Rodney, a homeowner and evergreen enthusiast with a passion for creating vibrant, thriving lawns in northern climates. Here at The Evergreen Edit, I share practical lawn care tips, seasonal advice, and my personal experiences to help you grow a yard you’ll love all year round.
