Just when you thought you were a lawn care pro, blemishes on your green grass appear. A common culprit to these brown spots or dead grass is a fungal lawn disease. Turf diseases tend to happen during wet conditions in the late spring or late summer and they can spread quickly even over an otherwise healthy lawn. Stopping dead patches or weak spots starts with an accurate diagnosis and early prevention.
Identify 10 Common Lawn Fungal Diseases
1. Brown Patch
When brown grass appears as irregular circular patches that can span several feet in diameter, you might have a Brown Patch infection. It's aggressive during warm, humid weather when it infects susceptible grasses.
- Thrives in air temperatures between 65°F and 85°F
- Brown patch lawn disease causes a circular "smoke ring" of darker grass around the edges. Thin white fungal threads may be visible. Infected blades may look water-soaked.
- Favors dense lawns where poor drainage creates moist conditions.
2. Dollar Spot
The dollar spot disease presents as small, straw-colored patches, about the size of a silver dollar. These spots of leaf damage can eventually grow and merge to form larger dead spots, especially if there is a nitrogen deficiency.
- Small circles of bleached-out dead grass about 1-2 inches in diameter can dapple an entire lawn during dry weather when cool night temperatures result in dew on the grass.
- Blades of grass will become dry and brittle over time but turf roots are usually unaffected.
- Dollar Spot Lawn Disease occurs with excessive thatch with compacted soil that causes low soil fertility.
3. Snow Mold (aka Microdochium Patch aka Fusarium Patch)
There are two varieties of this cold-weather fungus. Grey snow mold is ashy in color and only occurs after snow cover. Pink snow mold (pale pink to salmon colored) emerges with or without snow cover and is the more severe variety.
- Found in cooler climates with heavy snow cover and alkaline soil.
- Circular patches of matted grass with slimy leaf blades and a web-like, moldy covering.
- Occurs where late season fertilizing saturates a thick thatch layer under heavy, slow snow melt.
4. Powdered Mildew
A white or grayish powder-like substance found more often on cool-season grasses. It thrives in shaded areas with poor air circulation and compact soil.
- Affected grass looks as if it's dusted with flour or powder
- Leaf damage will cause the grass to thin or become stunted over time
- Ideal conditions are cool, prolonged wet periods with mild temperatures (~65°F)
5. Red Thread
Red thread lawn disease (aka pink patch) leaves pink or red fungal threads on the grass blades. The threads are usually seen in cool, damp weather and in lawns lacking proper nutrients.
- Thin, red or pink thread-like growths appear on top of already weak patches of grass
- Thread disease infects susceptible turfgrasses with low nitrogen levels and a thick thatch layer
- Areas infected with a thread disease will become most noticeable in spring or fall with rainy conditions
6. Fusarium Blights
Fusarium blight (different from Fusarium Patch!) is commonly found in cool-season grasses when temperatures exceed 85°F. It's become increasingly common as cool climates experience longer hot spells.
- Creates circular dead patches along sidewalks or driveways or unshaded areas with southern sun exposure.
- A tan/yellow or gray patch with a "frog-eye" pattern can emerge. A pink patch of fungi can appear on the soil surface as the disease progresses
- More prevalent in lawns under heat stress, cut too short.
7. Fairy Rings
Fairy ring disease creates bizarre rings of dark green grass, often accompanied by mushrooms. This fungal disease efficiently breaks down organic matter but can kill the grass by creating poor environmental conditions for healthy turf.
- These circular spots appear as dark green rings or arcs, ranging from a few inches to several feet wide.
- Often occurs as a surge after excess water is followed by hot temperatures
- Most susceptible are patches of grass near tree roots or old tree stumps with low sunlight exposure.
8. The Rust Diseases
This family of fungal infections are common lawn diseases. They appear as orange, yellow, or reddish-brown powder on the grass blades, resembling actual rust. Leaf rust tends to develop in undernourished lawns with slow-growing grass.
- Affected grass blades may have small yellow or orange spots from rust spores that easily transfer to shoes or tools.
- Patches of grass may yellow or appear thin or uneven.
- Most common in late summer or early fall during extended humid periods on compacted soil with poor microbial health.
9. Grease Spot (Cottony Blight or Pythium blight)
This turfgrass disease mostly affects warm-season grasses. It is highly destructive for lawns and golf courses.
- This leaf blight looks like irregular patches of greasy grass followed by fluffs of white or gray mycelium.
- Tends to occur during very hot summer days with humid conditions.
- It attacks the grass roots but is spread by wind, water, and during lawn mowing.
10. Summer Patch Disease
This fungal disease infects warm-season grasses. It's one of the most common in North America and it thrives on dry days with temperatures in above 80° F.
- Causes severe damage to the grass roots, leading to irregular dead patches of grass.
- Patches of grass several feet in diameter may turn yellow before dying, with roots appearing rotted or discolored
- Most common when grass isn't cut to the proper height and then experiences high, humid conditions.
Treating Grass Mold and Lawn Fungus
- Store-bought Fungicides: Products like Scott's DiseaseEx or Bayer Fungus Control can treat and prevent lawn diseases. Always read product labels for proper application of chemical treatments.
- DIY Fungicide: For a quick fix, you can mix water, baking soda, and dish soap for a homemade solution. Spray it on infected areas to slow fungal growth. For concentrated patches, mix equal parts water and hydrogen peroxide and spray on.
- Proper Lawn Care Maintenance: Aerate your lawn to break up compacted soil. Avoid overwatering. Mow to the correct height for your grass type. Clean up organic material (grass clippings, dead leaves). Apply a slow-release nitrogen fertilizer to keep your grass healthy (but avoid excessive nitrogen applications!)
FAQ
How can I prevent lawn fungi in the future?
Soil compaction or poor soil drainage will create moist spots that fungi thrive in. Improve water drainage with lawn aeration, and remove thatch buildup. Remove leaf litter or turf debris to give the lawn extra sun exposure. Monitor for infected leaves, lawn rust, yellow spots, or dead patches after a rainy period.
If you're replacing infected plants or dead turf, consider your grass type and choose one suited to your climate and environmental conditions. Know its needs to avoid applying excess nitrogen nor creating an alkaline soil.
Lawn care professionals may use lawn fungicides and chemical controls during high-risk seasons (e.g., late spring, humid summers or rainy weather).
Can lawn fungus go away without intervention?
Most grass diseases won't just go away. While some may stop spreading during hot weather and drier conditions, others thrive during hot summer days. Excessive thatch is a great hiding spot for fungal diseases to go dormant until their preferred conditions improve. If a lawn fungus has taken hold, chemical treatment/prevention with lawn fungicides and proper lawn care maintenance is essential to save infected turf.
Can I still mow my lawn if I have fungus?
Yes, but take safety precautions. Use smart lawn care practices. Only mow when the grass is dry. Remove turf debris. Clean your lawn care tools afterward to avoid spreading fungal spores to areas of healthy lawn. Minimize excessive watering and heavy traffic over recently infected turf - give grass a chance to enter an active growth phase to combat areas of infected lawn.
