Experiencing lawn fungal diseases can be a nightmare for homeowners who have worked hard to maintain a lush, green lawn. Fungal diseases manifest as brown spots, patches, or mushrooms that can quickly spread.
Despite proper lawn care, fungal spores can still infect your grass. That’s why it’s important to regularly inspect your lawn and address any abnormalities before they get out of control. This guide will help you identify and treat the most common fungal diseases to save your lawn.
What Causes Fungal Diseases in Lawns?
Several factors create favorable conditions for fungal diseases to take hold:
- Drought – Lack of moisture stresses grass, making it more vulnerable.
- Improper mowing – Cutting too short or infrequently weakens grass.
- Over/under watering – Too much moisture prevents drying, spreading disease. Too little causes stress.
- High heat and humidity – Fungi thrive in warm, humid conditions.
- Excess fertilizer – Too many chemicals damage grass roots and soil.
- Compacted soil – Prevents proper drainage and oxygen flow to grass roots.
- Overfertilization – Excess nitrogen causes succulent grass growth prone to disease.
- Nutrient deficiencies – Lack of potassium, phosphorus, etc. stresses grass.
Regular lawn maintenance like aerating, proper mowing, and balanced fertilization helps prevent diseases. But fungal spores are ubiquitous, so infestations can still occur. Let’s look at symptoms, causes, and treatments for common fungal diseases.
6 Common Lawn Fungal Diseases
1. Brown Patch
Brown patch is caused by a fungus called Rhizoctonia and is one of the most prevalent lawn diseases. Circular brown spots up to several feet wide appear across the lawn, often during summer’s warm, humid weather. As the spots grow together, large sections of grass die.
Treatment: Improve drainage and reduce watering frequency. Apply a fungicide containing azoxystrobin, myclobutanil, propiconazole, or chlorothalonil.
2. Dormant Grass
When grass turns brown and stops growing due to stressful conditions like drought, it has gone dormant. Dormancy is a protective mechanism that allows the grass to survive. The lawn will green up again once favorable conditions return.
Treatment: Water deeply and less frequently. Apply a balanced fertilizer when grass resumes growth. Overseed thin areas in fall.
Reddish-orange powdery growth on grass blades characterizes rust disease. It thrives in the cool, wet conditions of spring and fall. Rust is often seen in perennial ryegrass and Bermuda lawns. Severe infections stunt grass growth.
Treatment: Improve drainage and reduce watering. Apply nitrogen fertilizer to help grass outcompete the infection. Azoxystrobin, myclobutanil, propiconazole fungicides can help control rust.
4. Thatch Buildup
Thatch is a tightly packed layer of dead grass stems and roots between the green grass and soil. It prevents water, air, and nutrients from reaching grass roots. Thatch also harbors fungal spores and insect pests.
Treatment: Regular aeration helps break up thatch so microbes can decompose it. Mow frequently with a mulching mower to shred clippings. Overseeding improves competition against fungal growth.
5. Red Thread
This disease causes red or pink threadlike growth on grass leaves, stemming from fungal mycelium. Red thread appears in lawns with poor fertility that are stressed. If unchecked, it can kill entire sections of grass.
Treatment: Fertilize to improve grass health. Apply potassium which strengthens grass against infection. Water deeply and less frequently. Use a fungicide containing myclobutanil, propiconazole or chlorothalonil.
6. Dollar Spot
Circular tan spots with reddish-brown rings up to 2” wide typify dollar spot. A white, cobweb-like mycelium may appear at the border of spots in the early morning. Dollar spot thrives during cool, humid conditions.
Treatment: Improve drainage, fertilize, and reduce watering frequency. Mow with sharp blades to prevent leaf injury. Apply fungicide containing chlorothalonil, propiconazole, myclobutanil or mancozeb.
How to Prevent Lawn Fungal Diseases
While fungal spores are impossible to completely avoid, proper lawn care creates less favorable conditions for fungal diseases to take hold:
- Mow frequently at recommended height – Long grass shields fungus; short grass is stressed.
- Sharpen mower blades – Ragged cuts create entry points for disease.
- Water thoroughly, less frequently – Light watering increases frequency, spreading spores.
- Aerate compacted soil – Enables air and water circulation to roots.
- Apply balanced fertilizer – Don’t overdo nitrogen which causes succulent growth prone to fungus.
- Seed and fill bare spots – Improve turf density to outcompete fungal growth.
- Allow grass to dry before watering – Excess moisture encourages fungal spread.
- Remove clippings – Source of spores; mulching blades shred them into lawn.
- Adjust sprinklers – Target water to lawn, not pavement where it pools.
- Remove thatch – Harbors fungal spores, prevents air and water penetration.
Lawn fungal diseases like brown patch, dollar spot, and rust can quickly ruin a lush lawn. But catching them early and improving lawn care practices can help treat and prevent fungal disease without relying solely on fungicides. With proper mowing, watering, fertilization and aerating, your grass will be healthier and better able to ward off fungal invaders.
Frequently Asked Questions
Look for circular brown spots or patches, yellowing grass, orange powdery rust growth on blades, cobweb-like white mycelium, and dark red threadlike strands which indicate common fungal diseases.
Improve drainage through aeration. Water thoroughly and less frequently. Apply fungicide. Mow frequently with sharp blades. Remove clippings that harbor spores. Overseed to thicken turf. Ensure proper soil pH and fertility.
Look for fungicides containing ingredients like azoxystrobin, myclobutanil, propiconazole, chlorothalonil and mancozeb. Always follow label application instructions carefully.
Apply fungicide at the earliest sign of disease, or as a preventive measure when conditions favor fungal outbreaks – like spring and fall when weather is cool and humid.
Depends on the product, but typically fungicides are applied every 7 to 14 days until disease is under control. Then a maintenance application once a month during peak disease seasons may help prevent recurrence.