Lawn Fungus Identification Guide – Key Signs and Treatment

We all desire a lush green lawn, but oftentimes we don’t always get what we want, mostly due to lack of effort and/or applying the wrong lawn maintenance practices. 

What we do get is a lawn riddled with insects, pests, disease, and lawn fungus, which cause yellow patches and spots, discolored patches, and dead patches of grass. Learn about common lawn diseases that can affect your lawn.

Speaking of which, turf grass fungus, sometimes called brown patch is a common disease in lawns and occurs in any conditions including rainy conditions and cold weather conditions. 

There are several different types of lawn fungus that can affect your lawn grass including cool-season grass such as black spot, lawn rust, dollar spot, red thread, and fair rings disease.

Key signs of lawn fungus include circular yellow patches and fine white filaments on blades of grass and grass clippings. Here are 10 common types of turf fungus and how to treat lawn fungus to maintain a healthy lawn.

Lawn Fungus	Identification
Dollar Spot	Cotton candy-like growth and appearance/dark patches
Brown Patch	Circular brown patches on your lawn that can range in size between a few inches to several feet
Pythium Blight	A small circle of dark or brown grass, which gradually gets bigger as the fungus grows
Powdery Mildew	White, powdery spots or patches on top of the grass blades
Fairy Ring	Small circle of dark or brown grass, which gradually gets bigger as the fungus grows
Rust Lawn	Orange or rusty spots or completely coating a grass blade
Snow Mold	Web-like appearance/circles measuring approximately 3 to 12 inches in diameter
Red Thread	Pink or tan circular patches that measure between 1 inch to 2 feet in diameter
Lawyer’s Wig	White cylinders popping up from the ground, after which the bell-shaped caps open

What is Turfgrass Fungus?

Lawn fungus is a disease that is usually a result of extended periods of moisture due to improper watering techniques, changes in weather conditions and temperature, and other conditions that can affect your turf’s ability to fight infections.

Often called brown patches or brown spots, grass fungus is bound to appear in any lawn in the summer or any other season, even under snow, due to one or more reasons, such as a lack of nitrogen fertilizer. Here’s a list of common lawn diseases and fungus.

As I mentioned earlier, most fungi are beneficial to lawns as they help decompose organic matter, which then supplies nutrients for your grass.

Almost every lawn has dormant microorganisms and disease-causing lawn fungi, which are simply waiting for the right conditions to cause havoc to your turf, most commonly when your lawn is under stress. 

Unlike regular brown patches that go away with a little extra watering, turfgrass fungus brown patches don’t usually green up no matter how much water you add to your yard.

What Does Turfgrass Fungus Look Like? 

Turfgrass fungus typically appears as discoloration and/or spots on individual leaf blades, powdery blotches, grass blades wilting from the tip, and most commonly rings of mushrooms up to 2 inches in diameter.

This is where you need to pay attention because grass fungus can easily be confused with symptoms of other problems in your lawn.

These symptoms of turfgrass fungus begin to get worse as the disease progresses like enlarged spots, and in worse cases dying of the roots. See my article on the causes of grass fungus.

10 Lawn Funguses and Identification 

1. Identify Dollar Spot Lawn Fungus

Sclerotinia homoeocarpa, also known as dollar spot is one of the most common lawn fungus that usually appears when daytime temperatures are between 59-88° F (15-31° C). 

You can identify dollar spot by its round, straw-colored, or bleached-out spots, ranging in size between the size of a quarter to the size of a silver dollar.

Symptoms of dollar spot fungus such as tan or bleached-out lesions accompanied by reddish-brown bands are visible on individual grass blades. 

Dollar spot affects home lawns and golf courses and many grass types including fine fescue, perennial ryegrass, creeping bentgrass, Kentucky bluegrass, and annual bluegrass. 

This turfgrass fungus usually occurs in the summer and autumn and during periods of high humidity, warm days, and cool nights. 

What Causes Dollar Spot? 

Dollar spot fungus is caused by the pathogen Clarireedia Jacksonii (formerly Sclerotinia homoeocarpa), which develops when the climatic conditions are favorable for its spores to become active, causing the fungus to spread. 

How to Eliminate Dollar Spot Lawn Fungus? 

You can either use a fungicide on your turf or try one of many natural ways to get rid of dollar spot fungus. Adding to this, it is also important to add proper fertilization to your lawn when you treat grass fungus, which is a nitrogen-rich fertilizer in light and frequent applications. 

Since dollar spot is more severe in dry soil, keep your soil moist with a light, daily irrigation schedule. Neem oil is an effective natural remedy for dollar spot and should only be applied to diseased areas. 

If you’d like to eliminate dollar spot quickly, using a fungicide in favorable conditions is your best bet. Even though there’s a long list of chemical fungicides to kill dollar spot, BioAdvanced fungus control is perhaps one of the best fungicide treatments available for the disease. 

BioAdvanced fungus control does two things – kills existing dollar spot and other types of fungus including rust and brown patch and offers three months of protection. 

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2. Identify Brown Patch Fungus

Brown patch fungus is billed as the most widespread of all turf diseases and attacks all known grass types and species. 

As the name suggests, brown patches appear in circular brown spots on the lawn. This brown patch damage can range in size between a few inches to several feet. Here are a few more issues that can cause brown patches in your lawn.

Additionally, you may also notice brown borders (smoke rings) around these brown patches, especially during periods of high humidity. 

The first signs of brown patch fungus are a circular pattern of light-yellow discoloration that appears in your grass. This infected grass will eventually turn from orange to tan, which indicates that the fungus is spreading and infecting each grass blade. 

Although brown patch fungus affects all cool-season grasses, it causes more damage to tall fescue and ryegrass. It can also affect a variety of warm-season grasses including Bermuda, St. Augustine grass, and zoysiagrass. 

What Causes Brown Patch? 

Many things cause brown patch lawn fungus, most notably poor soil drainage in compacted soil, excessive nitrogen levels and incorrect irrigation practices, and excessive thatch. 

How to Eliminate Brown Patch Fungus? 

Many cases of brown patch fungus can be cleared by simply adhering to good lawn care practices. Next, hold off on using any fertilizers with nitrogen content as they promote the growth of fungi. 

Try to eliminate brown patch fungus by implementing correct cultural practices first before resorting to chemical methods. Remove the infected grass first before applying any fungicide. 

Scotts® DiseaseEX is a quick and effective fix for brown patch fungus. After proper application, it lasts up to 4 weeks and also prevents the spread of the disease to the rest of your turf. 

For more details, check out my article on getting rid of brown spots in your lawn.

3. Identifying Pythium Blight

Pythium blight may seem like a fancy name for a fashion label but is a lawn disease that can cause havoc in your lawn. 

Also called cottony blight owing to its cotton candy-like growth and appearance, pythium blight occurs in dark patches of grass measuring roughly ½” to 4” in diameter. 

Most pythium blight spots are greasy-looking and grey when wet and yellow when they dry out. Pythium blight may look normal at first like damp patches of grass that after some time develop grey mold. 

Once the infected grass dies, it becomes harder to spot the disease but you’ll see yellow patches in the areas the disease was present. 

What Causes Pythium Blight? 

Overwatering and excess fertilization are the two most common reasons for pythium blight. This lawn disease develops when nighttime temperatures exceed 65 degrees F in cool-season turfs and 50 degrees F in warm-season turfs and prefers lawns with poor drainage. 

How to Eliminate Pythium Blight? 

Start by fertilizing and watering your lawn sparingly. Further, aerate your soil to prevent excessive thatch buildup and relieve soil compaction. Water your infested grass earlier in the day to allow the leaf blades to dry before nightfall and prevent moisture buildup. 

Severe infestations of pythium blight may need a fungicide chemical treatment in dry weather and not wet weather. Fungicides are most effective against this lawn fungus during the greasy, dark green stage of the infection. After applying a fungicide, avoid heavy traffic in the area. 

4. Identify Powdery Mildew

Have you noticed white powder on your grass blades including tall grass and healthy grass? Well, you’ve probably got a case of powdery mildew – a lawn foliar disease that grows on grass leaves and flourishes when it’s warm and dry unlike other lawn fungal outbreaks and fungal threats that happen in late winter. 

Powdery mildew is one of the few lawn fungal diseases that’s easy to identify with its white, powdery spots or patches on top of the grass blades. 

Without proper treatment, these powdery spots spread to cover the entire grass blades including the undersides. Infected green grass will eventually look like you’ve spilled flour in your yard. 

What Causes Powdery Mildew? 

Powdery mildew is caused by many fungal species in the genera Phyllactinia, Sphaerotheca, and Podosphaera. It affects grass plants, fruit, and vegetable plants and favors humid conditions with temperatures around 68-81° F.

How to Eliminate Powdery Mildew? 

I believe good lawn care practices should be the first line of control against powdery mildew. There are two natural ways to eliminate powdery mildew and prevent extensive damage – milk sprays that are made with 40 percent milk, 60 percent water, and a baking soda solution. 

Mix 1 tablespoon of baking soda with 1/2 teaspoon liquid dish soap in 1 gallon of water. Spray this mixture on the infected grass including the undersides of the grass blades and near the roots. 

Organic treatments and antifungal products for powdery mildew are most effective before the onset of the infections or during the first signs of the fungal disease. 

For faster results, use Captain Jack’s Copper Fungicide to control and prevent powdery mildew and a wide range of other fungal mycelium and lawn diseases. The best time to spray organic and chemical curative treatments is in the early morning and never in the late afternoon. 

5. Identifying Fairy Ring 

Fairy ring disease is a strange lawn phenomenon that plagues your lawn in the form of rings, arc shapes, or irregular patterns. This lawn fungal growth generally occurs in spring and summer including mid-summer and late summer and humid weather, and in both cool-season turfs and warm-season turfs. 

This unique disease starts as a small circle of dark or brown grass, which gradually gets bigger as the fungus grows. 

The ring of the circle can develop mushrooms during spring and fall during times of excess moisture or heavy wet conditions. 

Advanced fairy ring symptoms include dark brown or dead grass circles that roughly measure between 2’ to 15’ in diameter. However, I’ve seen instances where fairy ring circles are as large as 150’ in diameter or more.

There are three types of fairy rings:

1. A raised patch of grass that’s darker in color,
2. Dead grass in a circular shape, and
3. A full ring of mushrooms. 

What Causes Fairy Ring Lawn Fungus? 

Fairy rings are caused by different types of fungus growing under thatch layers and under soil including compact soil. The fungus releases several small threads in a circular shape called fungal mycelium, which develops into mushrooms at the edge of the circle. 

Check out why there are mushrooms in your lawn.

The fungi that cause fairy rings feed on decaying organic matter like logs, leaves, and roots buried in the soil. 

How to Eliminate Fairy Rings in Lawn? 

Unlike rust diseases or other common types of disease, fairy rings do not damage your lawn but their common symptoms are an eyesore. Plus, fairy rings often disappear on their own under the right environmental conditions, so waiting it out is perhaps the best way to bid adieu to this disease. 

However, it’s important to note that fairy rings are less likely to crop up in well-maintained lawns so do not use dull blades to cut grass, make sure there’s good airflow in your yard, use correct irrigation practices without causing any irrigation stress, and apply correct fertilization techniques and fertilization practices. 

6. Identifying Rust Lawn Disease 

Rust is a pretty unusual lawn disease that can be easily identified when you inspect the glass blades up close. Lawn rust (puccinia spp.) is similar to powdery mildew but instead of white powder appears in the form of orange or rusty spots completely coating a grass blade. 

At the onset of an infestation, lawn rust appears as small, yellow dots on grass blades, which can also be caused by insects such as caterpillars and beetle grubs. 

But you can tell if lawn rust is the cause of the issue by the rust-colored tufts of the powdery residue as the disease develops. 

Less severe lawn rust infections can make your grass grow slower than usual and severe infections can discolor the entire length of the grass blades, eventually causing them to point downwards instead of standing up. And this weakened state can make your lawn susceptible to other lawn diseases. 

What Causes Rust Lawn Fungus? 

According to the University of Illinois Extension Agriculture Program, there are a few key causes of lawn rust fungus consistent, excessive heavy rain, cool nights and heavy dew coupled with heavy rainfall, cloudy, humid weather followed by hot sunny weather, and low levels of nitrogen fertilizer and/or low water availability. 

How to Eliminate Rust Lawn Fungus? 

The sure shot way to get rid of rust lawn fungus is by focusing on the overall health of your lawn. A healthy, robust lawn is in a better condition to fend off diseases, and regular lawn care is a big part of this equation. 

Since your lawn is infected with rust lawn disease, it may be a good time to aerate your lawn since fungi often prefer moist soil and poor drainage. 

You should only apply a fungicide if the rust lawn infestation is at a severe stage, and before going dormant for the winter. 

Daconil is an effective fungicide against rust lawns and other lawn funguses and offers 3-way control. It starts controlling the disease upon contact and can be used in lawns as well as on vegetables, fruits, and flowers. 

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7. Identifying Snow Mold Lawn Fungus

Also known as snow rot, snow mold is a type of lawn fungus that forms when wet leaves or snow cover remains on the lawn for too long. 

Snow mold lawn fungus can affect any grass type that experiences cold temperatures and snow cover and can cause ongoing damage to your turf if left untreated. 

There are two types of snow mold fungus – gray snow mold and pink snow mold. Gray snow mold is less severe of the two types and damages just the blades of grass whereas the pink snow mold can destroy the crowns and roots of grass. 

About damage, snow mold is active during the winter, but you’ll only notice the damage in the spring as the snow melts. 

Pink and grey snow molds often grow side by side and although both feature a web-like appearance, they work a bit differently. Circles measuring approximately 3 to 12 inches in diameter are the first symptoms of snow mold fungus and keep growing as long as your lawn stays cold and wet. 

What Causes Snow Mold Fungus? 

Snow mold is caused by cold weather soilborne fungi that grow at freezing or near freezing temperatures. Heavy, deep snowfall and completely frozen ground add weight to grass blades, resulting in the formation of snow mold. 

How to Eliminate Snow Mold Fungus?  

There aren’t any fungicides that work against snow mold fungus during the spring when the snow melts. You can however apply Scotts DiseaseEx as a preventative measure in the fall before the first heavy snowfall. 

8. Identifying Red Thread Fungus

Red thread fungus is another common lawn fungus that is found in residential as well as commercial lawns like parks and golf courses. If your grass is topped with pink string and you didn’t throw a party the day before, then it’s probably red thread fungus. 

From a distance, red thread fungus looks like pink or tan circular patches that measure between 1 inch to 2 feet in diameter. But if you look closely, these patches are a mix of healthy grass and infested grass that’s typically tan or white. 

Red thread fungus is often mistaken for dollar spot and snow mold fungus but is set apart with its pinkish or red antler-like threads that stick out from the infected grass blades. 

Also known as sclerotia, these red threads are about ½-inch long and sometimes feature web-like mycelium in humid and wet weather conditions. 

What Causes Red Thread Fungus? 

There are plenty of factors that can make your lawn susceptible to red thread fungus like high temperatures and excessive moisture, cool and wet spring and fall conditions, poor access to sunlight, excessive traffic, drought, and low fertilization. 

How to Eliminate Red Thread Fungus? 

Just like most lawn funguses, the key to eliminating red thread fungus from your lawn is a good lawn care routine. Conditions that make your lawn attract red thread disease such as poor fertilization and sunlight need to be corrected to prevent future occurrences of the disease. 

Chemical control products are available but read the product label to ensure they can tackle red thread fungus. In most cases, using chemical antifungal products is unnecessary as long as you implement the right cultural practices. 

9. Identifying Lawyer’s Wig Disease 

Lawyer’s wig, also called shaggy inkcap is a large and conspicuous edible fungus that usually appears in woods, meadows, and roadside verges but can grow in residential lawns too. 

The young fruit bodies of lawyer’s wig first appear as white cylinders popping up from the ground, after which the bell-shaped caps open. 

This lawn fungus is aptly named (ink cap) for its white gills beneath the cap that gradually turn pink and black. Once the mushroom turns black, it dissolves itself quickly, sometimes in a matter of hours after being picked. 

What Causes Lawyer’s Wig Fungus? 

Lawyer’s wig fungus thrives in various habitats and even though they can grow singly, they are usually seen in large numbers. There are a few types of lawyer’s wig mushrooms, all of which can be grown indoors or outdoors. 

How to Eliminate Lawyer’s Wig Mushrooms? 

Lawyer’s wig mushrooms auto-digest themselves so there’s no need to use a fungicide or even pick them. They don’t last long but you can handpick them if you feel they are an eyesore on your lawn. 

10. Identifying Gray Leaf Spot Fungus

GLS, short for gray leaf spot is a foliar fungus that affects all types of turfgrasses. It typically develops when temperatures are between 75 and 95 degrees Fahrenheit, and is regarded as a serious fungal disease for corn fields in the United States. 

Also referred to as Magnaporthe grisea, gray leaf spot disease can be identified by oblong leaf spots. The center of these leaf spots features a gray felt-like growth after consistent periods of warm moist conditions. 

Gray leaf spots can range in color from olive green to brown with a dark brown border. In severe outbreaks of gray spot fungus, thin and generally unthrifty strands may appear and a closer look will reveal several spots. 

What Causes Gray Leaf Spots? 

Gray leaf spot lawn fungus is caused by extended periods of warm rain spells, during which the grass blades continue to remain wet. These conditions are ideal for gray leaf fungus pathogen growth, infection, and colonization. 

How to Eliminate Gray Leaf Fungus?

You can use chemical pesticides like azoxystrobin, pyraclostrobin, or fluoxastrobin to control gray leaf fungus. When applied properly, these fungicides help eliminate gray leaf fungus within 14 days. 

The active ingredients are available in a variety of brands and are great methods for disease management. 

Final Thoughts 

Just like pests, lawns can attract one or more fungal diseases but there’s no need to break a sweat as most can be treated with natural or chemical treatments and with effective active ingredients. 

Lawn fungus preventative measures include watering your turf during cool periods (early in the morning), removing excess thatch buildup from the infected turf, and applying adequate amounts of nitrogen fertilizer after performing a soil test by taking a soil sample.