How to Identify and Treat Grass Fungus

When your lawn starts to look more pink than green, that means something weird is growing on your grass –– fungus! But not every fungal disease is pink or comes with a batch of mushrooms (which, no, you shouldn’t eat). Learn how to identify and treat grass fungus so you can keep your lawn green, healthy, and mold-free. 

What is turfgrass fungus?

Like a shapeshifter, turfgrass disease can appear in many different colors, textures, and shapes on your lawn. Parts of your yard might be spewing different shades of red, you might identify web-like mold growth, or perhaps unusually shaped patches are popping up in the turf.

If this chaos sounds like your lawn, then a fungus is likely the culprit. 

What causes fungus to grow in my lawn?

A disease-causing pathogen needs two things for it to flourish: a host and the right environment. 

Your grass type will play a significant role in whether a fungal disease can prosper. Why? Because some turfgrasses make better hosts for certain diseases than others. 

Weak lawns that are poorly maintained provide an ideal environment for fungal disease. So if you’ve been slacking on your lawn care chores, like mowing, dethatching, and fertilizing, then you’re sending an open invitation to grass diseases. Yikes! 

How to prevent turfgrass disease in the lawn

Maintaining a healthy lawn is the best way to keep your grass disease-free. Tall grass, thatch buildup, and moist environments are among the many attractive conditions in which fungus thrives. As much as you want to skip aerating the soil this year or removing the autumn leaves, you might want to think twice before you ignore the lawn. 

Here are 15 lawn care treatments you can do to help nourish a vigorous lawn that’s resistant to disease: 

• Remove leaves and other debris from the lawn. Otherwise, diseases will overwinter in debris and take hold of your grass in spring.  
• Mow the grass regularly. Letting your grass grow too tall will create a hospitable environment for disease. 
• Leave behind grass clippings. Grass clippings act as mulch by locking in moisture and adding healthy nutrients to the soil. Keep in mind that if a disease is already infecting your lawn, you’ll want to remove grass clippings so that the fungus doesn’t spread. 
• Perform proper irrigation practices. Watering for long periods less often is healthier for your lawn than watering for frequent, short periods. Water your turf in the early morning before 10 a.m. Watering your turf in the evening is unhealthy for your lawn. Why? Because the water will cling to the grass blades overnight, creating a moist environment that invites pests and disease. 
• Invest in a sprinkler system. Sprinkler systems cater to your lawn’s exact moisture needs and apply uniform levels of water across the entire lawn. Some sprinkler systems are automatic, which means they’ll turn on without you ever having to lift a finger. 
• Grow a type of grass that’s disease-resistant and suitable for your lawn. The last thing you want is to grow cool-season grass in an area with long, scorching hot summers. Talk to a lawn care professional about the best turf for your lawn and which cultivars are most resistant to the common fungal diseases where you live.
• Test your soil and add amendments. You can’t have healthy turf if the soil it grows in is poor. Test your soil’s health so you can determine the best way to improve it. 
• Fertilize your grass. Just like you need food to grow, so does your grass.
• Aerate the soil. Aeration relieves compacted soil by creating small holes in the ground. The holes allow water, oxygen, and nutrients to reach the roots. 
• Remove thatch. Thatch is the buildup of dead organic matter that accumulates between the soil layer and turf. Fungus loves to live in thatch. Remove thatch when the layer reaches ½ inch or more.
• Overseed the lawn. Help prevent your yard from thinning by overseeding the lawn once a year. It’s a good idea to overseed with a disease-resistant cultivar. 
• Remove existing weeds. Weeds compete with your turf for space, light, moisture, and nutrients. A severe weed invasion can weaken your turf and make it vulnerable to pests and disease.  
• Apply pre-emergent herbicide. You can help prevent weeds from popping up by applying a pre-emergent herbicide. 
• Control grubs and other pests. Grubs are a common lawn pest, and they weaken your turf by feeding on the lawn’s root system. 
• Spread a ½-inch layer of compost across the lawn. Compost is a nutritious soil amendment. You can spread the compost with a rake or brew a compost tea. 

Chemical control: If your lawn has a history of fungal disease, then applying chemical fungicides as a preventative measure can prove effective. 

How to treat turfgrass diseases

Different types of turfgrass disease have specific treatment methods, but in general, the best treatment is to improve your lawn care practices. Why? Because putting specific cultural routines in place and enhancing lawn maintenance makes the environment less hospitable for the fungus. 

For example, if you’re dealing with a fungus that likes a moist environment, then you’ll need to improve your watering regime so that the lawn doesn’t remain wet for long periods. 

A fungicide may help control severe infestations, but it’s not always the best treatment method. Fungicides typically prove most effective when you apply them as a preventative measure. The best way to treat a turfgrass disease is with the maintenance practices we listed above. 

11 types of turfgrass fungal diseases and how to treat them

1. Brown patch

Causal Agent: Rhizoctonia solani

Turf Types Affected: Brown patch affects all warm- and cool-season turfgrasses, particularly tall fescue and ryegrass. 

Symptoms: Brown patch typically forms irregular circles of thin, light brown grass. The patches range between a few inches to several feet in diameter. The turfgrass inside the circle’s center sometimes recovers, resulting in a donut-like shape. 

Brown patch symptoms often resemble the signs of dog urine stains, drought, and grubs. Identify the disease by checking the grass in the early morning for white mycelium, a web-like substance that forms between the affected area’s leaf blades. 

When the disease is severe, it can spread rapidly across a large area without forming a circle.

Conditions for Disease: Poor aeration, overwatering, poor drainage, and high nitrogen levels make an attractive environment for this midsummer disease. Rainy weather, high humidity, night temperatures above 70 degrees, and daytime temperatures 80 degrees or above also contribute to brown patch’s success. 

Treatments: 

• Correct your watering regime.
• Water in the early morning instead of the evening.
• Remove grass clippings after you mow (otherwise, you’ll spread the disease).
• Remove excessive thatch buildup.
• Mow the lawn regularly.
• Apply a fungicide in the affected area. Most fungicides list a curative and preventative application rate. 
• Avoid nitrogen applications when the disease is active.

2. Dollar spot

Causal Agent: Clarireedia jacksonii (formerly Sclerotinia homoeocarpa)

Turf Types Affected: All species of warm- and cool-season turfgrass are susceptible.

Symptoms: Dollar spot appears as tan spots 2 to 6 inches in diameter sprinkled across the lawn. Many of the spots are the size of a silver dollar (hence the name). Dollar spot is active in late spring through fall. 

Affected grass blades have hourglass-shaped lesions with bleached centers and brown to purple borders. In the mornings, you might see cobweb-like mycelium coating the turf. 

If favorable conditions allow the disease to spread, the spots may merge to create large areas of dead grass. 

Conditions for Disease: Dollar spot infects lawns that have dry soil and low nitrogen levels.

Treatments: 

• Apply adequate nitrogen fertilizer.
• Remove thatch buildup.
• Correct your irrigation regime. Remember to water deeply and less often to promote a robust root system. 
• Mow grass regularly.
• Apply a fungicide to help prevent further infection as you make corrective cultural measures. 

3. Anthracnose 

Causal Agent: Colletotrichum cereale (formerly Colletotrichum graminicola)

Turf Types Affected: The most susceptible turfgrasses are annual bluegrass and creeping bentgrass. 

Symptoms: Anthracnose is most severe in early spring when temperatures are cool and midsummer when the weather is warm and humid. The disease appears as reddish-brown patches which fade to yellow and then tan to brown. Elongated, reddish-brown lesions with yellow halos develop on individual grass blades. 

Anthracnose can spread from the grass foliage to the crown and roots, resulting in basal rot (the crown is the base of the grass plant). 

Spiny, black fruiting bodies called acervuli may appear on infected grass. 

Conditions for Disease: Anthracnose favors high humidity, wet leaves, and grass under stress. Stress factors include high temperatures, low or unbalanced fertility, drought, poor drainage, compact soil, insect damage, thatch buildup, and low mowing heights. 

Treatments: 

• Correct fertilization and watering regimes.
• Remove excessive thatch.
• Aerate compacted soil.
• Avoid scalping the lawn.
• When changes to your lawn routine don’t produce results, the Clemson Cooperative Extension recommends applying a fungicide containing propiconazole or azoxystrobin with propiconazole. Always apply chemicals according to the product label directions. 

4. Leaf spot and melting-out 

Causal Agent: Drechslera spp. and Bipolaris spp. (formerly Helminthosporium spp.)

Turf Types Affected: Many turfgrasses are susceptible to leaf spot and melting-out, but Kentucky bluegrass, perennial ryegrass, and bermudagrass are the most severely affected. 

Symptoms: Disease symptoms can occur in spring, summer, and fall. Turf blades develop small brown spots after infection. As the disease progresses, the spots enlarge and develop tan centers with brown or purplish-red borders. The leaf tissue surrounding the spots begins to yellow.

The melting-out phase, which is more detrimental to the turfgrass than the leaf-spotting phase, results in the dieback of the crown and roots. The grass tissues rot and turn black, and the turf begins to thin. 

Conditions for Disease: High nitrogen fertilizer, thick thatch, excess water, wet weather, and short mowing height. 

Treatments: 

• Overseed lawns with a resistant cultivar.
• Avoid high nitrogen fertilization.
• Correct your watering regime so that the lawn isn’t wet for long periods.
• According to the PennState extension, spring and summer fungicide applications performed in the early stages of leaf spot are the most effective. Products containing iprodione, chlorothalonil, mancozeb, fludioxonil, azoxystrobin, or penthiopyrad typically provide good leaf spot control. 
• Applying fungicides in the melting-out phase is usually not effective. 

5. Pink snow mold 

Causal Agent: Microdochium nivale

Turf Types Affected: Bentgrass, annual bluegrass, fescue, perennial ryegrass, and creeping bentgrass are commonly affected by pink snow mold. 

Symptoms: Pink snow mold occurs in early spring or late winter but can appear in late fall if conditions are right. Infected grass develops circular patches that typically range from 2 to 10 inches in diameter, although some patches may merge to create a large area of affected turf. 

The patches often start small and will enlarge as cold weather conditions continue. Patches appear as gray, tan, or light pink matted grass with a white center. 

Conditions for Disease: Pink snow mold typically develops underneath deep snow covers that remain on the turf for a long time. The longer the snow covers stay on the grass, the greater the infection. Pink snow mold can occur even without a snow cover, as long as conditions are cold and wet. 

Susceptible lawns have tall grass, high levels of nitrogen fertilizer, poor soil drainage, or recent grass seed that had not matured before winter. 

Treatments: 

• Remove piling snowdrifts.
• Rake diseased areas to break up matted grass.
• Avoid applying high nitrogen fertilizer.
• Remove excessive thatch.
• Pink snow mold usually becomes less active when the turf dries and the air temperature rises.

6. Gray snow mold 

Causal Agent: Typhula incarnata

Turf Types Affected: Gray snow mold primarily affects cool-season grass. 

Symptoms: Symptoms appear in late winter or early spring as large snow covers melt away. White or tan crusted patches of dead and matted grass develop. Patches can range between a few inches to several feet in diameter. Gray fungal mycelium often appears on infected turf near receding snowbanks. 

A notable symptom that can help you distinguish the disease from other snow molds is the presence of small, reddish-brown, rounded fungal structures (known as sclerotia) on the crowns and blades of infected turf. 

Conditions for Disease: Growing conditions for gray snow mold are similar to pink snow mold. The disease develops underneath large snow covers that last for a long time. The longer the snow covers remain, the more severe the infection. But unlike pink snow mold, which can exist without a snow cover, gray snow mold can only occur if snow covers it. 

Your lawn is vulnerable to gray snow mold if you applied high amounts of nitrogen fertilizer, recently planted grass seed that did not mature before winter, or did not cut the grass before winter.

Treatments: 

• Remove piling snowdrifts.
• Rake crusted, matted areas.
• Avoid using high nitrogen fertilizer.
• Applying fungicide to an existing infection won’t prove very effective.
• Affected turf will likely recover in spring with proper maintenance.

7. Red thread 

Causal Agent: Laetisaria fuciformis   

Turf Types Affected: Red thread typically infects perennial ryegrass, fine fescue, Kentucky bluegrass, and bentgrass. 

Symptoms: This fungal disease occurs in spring and fall but can also occur in summer when rain persists. Irregular patches of pink develop in the yard. 

In the late stages of the disease, reddish threads of fungal mycelium grow at the tips of the affected blades. Red thread affects the turf’s leaf, stem, and sheath, but severe infections can kill the whole plant. When the turf dies, the affected areas turn light pink or tan. 

Conditions for Disease: Lawns with inadequate nitrogen fertilizer and excessive moisture are an attractive host for red thread. 

Treatment: 

• Apply adequate levels of nitrogen fertilizer.
• Practice good watering techniques so that your lawn doesn’t remain wet for too long. 
• Fungicides are usually not necessary to treat red thread. If the infestation is severe and a fungicide is warranted, you’ll need a licensed applicator to apply the product for you.  

8. Summer patch 

Causal Agent: Magnaporthe poae

Turf Types Affected: Annual bluegrass, Kentucky bluegrass, and fine fescues are the most affected grass types. 

Symptoms: Summer patch symptoms look like crescent-shaped or circular patches with slow-growing, thin, wilted grass. In many cases, healthy grass grows in the patch’s center. Patches range from a few inches to 3 feet in diameter and can merge to create a sizable infected area. 

Summer patch bears a resemblance to other turf diseases and turf injuries associated with drought and heat stress. For successful identification of summer patch, a qualified diagnostician must look at the affected turf with a microscope. 

Conditions for Disease: Summer patch is root disease. Improper cultural practices promoting shallow root systems will make your lawn susceptible to the fungus. Favorable disease conditions include heat and drought stress, low mowing heights, frequent and light irrigation, soil compaction, excessive thatch, and unbalanced fertility. 

Treatments:

• Aerate compacted soil.
• Mow your grass at the highest recommended mowing height.
• Develop a balanced fertilizer regime.
• Avoid fertilization practices that promote top growth at the expense of root development. 
• Follow proper irrigation practices. Water the lawn less often and for long periods. Water in the early morning instead of the evening. 
• Reduce thatch.
• You can resort to fungicides for summer patch control, but they are more effective as a preventative measure. 

9. Powdery mildew 

Causal Agent: Blumeria graminis

Turf Types Affected: Kentucky bluegrass is the most commonly affected grass.

Symptoms: The first sign of powdery mildew appears as isolated, white spore masses developing on the grass blades. The white masses may eventually cover the whole blade, making the turf look as if it’s sprinkled in flour. If you look closely, you might see tiny black fruiting bodies within the white powdery growth. 

Severely infected grass will turn yellow and possibly die. The reason for the dead turf is less likely powdery mildew and more likely weak turf succumbing to other stresses, such as drought or another disease.

Conditions for Diseases: Kentucky bluegrass growing in the shade is the ideal host for powdery mildew. Other conditions include poor air circulation, high humidity, and cool air temperatures.

Treatments: 

• Increase sunlight in affected areas.
• Remove or transplant plants that are inhibiting air circulation around the infected turf.
• If you cannot modify the turf’s environment, the Clemson Cooperative Extension recommends applying fungicides containing myclobutanil, propiconazole, or triadimefon.

10. Rust 

Causal Agent: Puccinia spp., Uromyces spp.

Turf Types Affected: Kentucky bluegrass, perennial ryegrass, tall fescue, and Zoysiagrass are the most severely affected by rust.

Symptoms: The most common turfgrass rust diseases are stem rust (Puccinia graminis), stripe rust (Puccinia striiformis), crown rust (Puccinia coronata) and leaf rust (Uromyces spp.). An early sign of rust is yellow speckling of the blade and stem. 

As the yellow areas grow larger and spread, the leaf eventually ruptures and releases yellowish-orange to reddish-brown spores. Orange powder will collect on your shoes and fingers when you walk on or rub the infected turf. 

Conditions for Disease: Rust occurs in early spring through mid-summer and thrives in moist areas with low sunlight. Turfgrasses with low nitrogen levels or irrigation stress are particularly susceptible to fungal disease. 

Treatments: 

• Apply adequate levels of nitrogen.
• Reduce shade by trimming trees and bushes.
• Improve air circulation by aerating your soil.
• Correct irrigation practices.
• Fungicides are not always necessary, but severe rust infections may benefit from chemical treatment. 

11. Fairy ring

Causal Agent: Many different species of fungi in the fungal group basidiomycetes cause fairy ring. 

Turf Types Affected: All grass types are susceptible to fairy ring disease. 

Symptoms: Fairy ring symptoms vary depending on the fungal species infecting the lawn, but a common symptom is circular or semi-circular rings forming in the infested grass. 

The border of the circular rings may appear darker and faster-growing than normal-colored green turf. Older rings may have a band of dead grass with green grass in the middle. Grass within the circles may appear a normal-colored green, declining, or dead. A ring of mushrooms may grow during moist or rainy conditions. 

The dark green turfgrass is caused by the fungus releasing nitrogen when it decomposes organic matter. The nitrogen gives that grass an unexpected nutrient boost. The brown-colored grass is caused by the fungus forming an almost waterproof layer in the soil that prevents water from reaching the turf’s root system. 

Conditions for Disease: Fairy ring occurs in spring through early summer. The fungus favors light-textured soil, turf low in nitrogen, low soil fertility, drought, and excessive thatch. 

Treatments: 

• Reduce thatch with a verticutter.
• Aerate the infested area.
• Remove nearby tree stumps and tree roots to reduce the organic matter on which the disease feeds. 
• Fertilize inside the ring to stimulate new growth.
• Drench the brown-colored areas with a wetting agent (a chemical that helps water penetrate and spread) to enable water to access the roots. 
• Fungicides for this disease are most effective when you use them as a preventative treatment.

FAQ about grass fungus

Consider all your treatment options

Mowing, dethatching, aeration –– treating fungal disease is hard work. Not only do you need to fertilize and irrigate the lawn to treat a disease, but you also need to perform proper maintenance tasks year-round to ensure an infestation doesn’t reoccur. That’s a whole lot of time to spend on your lawn. 

Take the load off your shoulders and hire a local lawn care professional. Hand the to-do list over to a pro so you can focus your attention on the people, goals, and hobbies that matter to you most. Don’t let fungus, a spore-producing organism that’s anything but fun, steal your time and energy.  

Main Photo Credit: Andrew Skudder | Flickr | CC BY-SA 2.0