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Lawn Fungus Control: A Complete Guide to Getting Rid of Grass Diseases

Keith Hardy - Bio Photo
Keith Hardy
Senior Editor

Keith has been involved in the gardening and landscaping industry for the past 21 years. From a jobbing gardener to running his own landscaping services....

  • Learn to identify common lawn fungal diseases like dollar spot and brown patch
  • Apply appropriate fungicides like propiconazole according to label directions
  • Practice prevention by improving lawn conditions and care practices
  • Seek professional help for widespread, rapid, or stubborn infections
  • Act quickly at the first sign of fungal disease to prevent major lawn damage

A healthy, lush lawn is a dream for many homeowners. But that perfect turfgrass can quickly turn into a nightmare when lawn fungi and other grass diseases take hold. Brown patches, yellowing, dead spots – these are all signs of a fungal infection.

A lawn fungus is a turfgrass disease that infects grass blades and their roots resulting in both visual and physical damage to a lawn. Once infected a fungus can spread rapidly. It is therefore essential to understand what can cause a fungus and how to control and eradicate it to ensure a healthy-looking lawn.

The key is early intervention. By learning how to identify and treat common fungal diseases, you can get your lawn back to its former glory. Below, we will look at the factors that cause and influence the spread of grass fungi as well as examine the most common type of fungi that affect lawns together with various treatments available to eradicate the problem and prevent it from happening again.

What Causes Lawn Fungus?

The same diseases that affect lawn weeds also affect lawn grass. Lawn fungi are microscopic organisms. They live in the earth, air, and water. Fungi help to break down dead grass clippings. They also help to break down dead leaves. Some fungi are beneficial. They help to break down the nutrients in dead grass. Other fungi are harmful. They attack living grass and cause disease.

Before we dive into treatments, it helps to understand what conditions cause grass fungi to develop and spread in the first place.

Lawn fungi thrive in the warm, humid conditions of summer. And they spread aggressively, infecting vast swathes of your yard. Left untreated, the fungus can damage or even kill your grass. The main contributors are:

  • Wet weather – Excess moisture from heavy rainfall, irrigation, or high humidity provides the perfect moist environment for fungus growth.
  • High temperatures – Most fungal spores thrive in summer’s heat. Temperatures above 85°F (30°C) overnight are especially problematic.
  • Poor air circulation – Still air gets trapped among grass blades, keeping the lawn constantly damp.
  • Low soil nutrition – Hungry grass has a weakened immune system, making it more vulnerable to pathogens.
  • Mowing practices – Dull or unclean mower blades can spread spores from infected to healthy grass.
  • Shade – Fungi proliferate in the consistently damp, low-light conditions found under trees or shrubs.

By understanding these factors, you can take steps to prevent conditions that allow fungal diseases to take hold in the first place.

How to Identify Common Lawn Fungi

Lawn DiseaseDescription
Dollar SpotThis disease creates small, round dead spots about 2-4 inches wide on grass blades. The spots are tan, yellowish, or straw-colored.
Brown PatchCauses roughly circular patches up to several feet wide. Affected areas turn brown or straw-colored. Often occurs after hot, humid weather.
Pythium BlightAggressive disease that spreads rapidly in hot, wet conditions. Causes yellowing and wilting before turning grass straw-colored or brown.
Red ThreadCreates round or crescent-shaped patches up to 6 inches wide. Blades are covered in a pinkish-red or rust-colored thread-like growth.
Snow MoldTwo varieties – gray and pink snow mold. Forms in winter during snow cover, causing matted tan or gray patches. Pink variety has cottony pink growth.
Summer PatchYellowish patches up to several feet wide that emerge in hot weather. Roots and crowns of affected plants turn brown.
RustYellow, orange, or reddish-brown powdery spores on grass blades. Usually occurs when the lawn is stressed or lacking nitrogen.
Damping-Off DiseasesAffect seedlings and young plants, causing them to rot at or near the soil line. Infected seedlings may wilt, collapse, and die. Favored by moist conditions.
Powdery MildewAppears as white, powdery growth on grass blades, leading to yellowing and distortion of leaves. Favored by dry conditions.
Take-all PatchCauses irregular, sunken patches of yellow or brown grass. Roots become rotted and darkened. Troublesome in cool, wet conditions.
Leaf Spot and Melting-Out DiseasesCause small, dark lesions on grass blades that can coalesce, leading to thinning and “melting-out” of the turf. More active in warm, humid conditions.
AnthracnoseAffects various grasses, appearing as irregularly shaped, sunken patches of yellow or brown grass. Can cause blighting and dieback of grass blades. More severe in hot, humid weather.
Take-All Root RotTake-all root rot is a soil-borne fungal disease caused by the Gaeumannomyces graminis var. graminis pathogen. The disease caused by this fungus attacks grass roots, causing them to rot, whither, and die.
Common Lawn Fungi

The first step in treating lawn fungus is to correctly identify the particular disease affecting your yard. Here are the most common fungal infections you may encounter:

See also  Dollar Spot Fungus | What Kills Dollar Spot Fungus

Dollar Spot

Lawn Fungus Control - Dollar Spot
Lawn Fungus Control – Dollar Spot

Dollar spot lawn disease is a moderately serious disease that affects Kentucky bluegrass, creeping bentgrass, creeping red fescue, tall fescue, perennial ryegrass, and bermudagrass. It is caused by the fungus Sclerotinia homoeocarpa (formerly Sclerotinia homoeocarpa). This fungus causes small, irregularly shaped, sunken spots that measure 2 1⁄2” to 4” in diameter on turf. These spots can range in color from straw to tan to black. Dollar spot lawn disease typically occurs during the spring and fall, and results in unsightly turf turfgrass.

The fungus responsible for dollar spot lawn disease survives in infected plant debris and in the soil. The disease is spread through infected seeds, infected sod, infected sprigs, and infected stolons. Dollar spot lawn disease is most active when the soil temperatures are between 68°F and 86°F, and when the relative humidity is between 80% and 95%.

The disease is not active when temperatures are below 50°F or above 95°F. Optimum conditions for dollar spot lawn disease occur during heavy dew, fog, and just after rainfall.

Dollar spot lawn disease can affect a lawn when the grass is under stress. These stresses include too much or too little water, poor soil, poor drainage, compacted soil, drought, poor fertility, and mowing the grass too short.

Dollar spot fungus and how to combat it.

Brown Patch

Lawn Fungus Control - Brown Patch
Lawn Fungus Control – Brown Patch

In some cases, brown patches may appear on your lawn. These are actually fungal infections (Rhizoctonia solani) caused by grass being wet for extended periods of time. They look like small, circular spots and they’re usually found near the base of your grass. It is most commonly seen on tightly mowed lawns like golf courses.

It can be cured using chemical ant fungal treatments containing Benzimidazoles. If it becomes a recurring problem then look to overseed the areas with more fungal resistant grass types.

An in depth look at brown patch and how to prevent and eliminate it.

Pythium Blight

Lawn Fungus Control - Pythium Blight
Lawn Fungus Control – Pythium Blight

Pythium is a water-loving fungus that attacks weakened grass plants. It often appears in lawns and turf during prolonged wet weather. It rapidly emerges in hot humid or wet weather, rapidly spreading from plant to plant and plant parts. In severe cases, it may kill grass plants. Pythium can cause rapid turf loss on large areas of lawn.

Affected areas start as small circular patches up to about six inches wide but may expand rapidly to cover large areas. Affected areas may be uneven, characterized by bare patches or thinning turf. Affected areas may be muddy, with standing water. The grass may appear yellow or straw-colored, with wilting or loss of grass color.

A more detailed look at Pythium blight and how to eliminate it

Red Thread

Lawn Fungus Control - Red Thread
Lawn Fungus Control – Red Thread

Red thread (Laetisaria fuciformis) is similar to lawn rust and often classed together although actually a separate fungus. It is among the most prevalent fungal patch illnesses detected on lawns, and it is especially prevalent in areas where the grass is lacking in nutrients such as nitrogen. It causes dark patches of grass to appear on the lawn, particularly during a rainy summer.

Red Thread and how to eliminate it.

Snow Mold

Snow mold diseases come in two varieties gray and pink snow mold (fusarium patch). Unfortunately, they are fairly common lawn diseases that appear as brown patches or pinkish circles on the lawn. They can be two of the most destructive grass fungi diseases, and it may be very difficult to treat once established. Autumn (Fall), winter, and early spring are the most common times of year to encounter this pest, although infestations may occur at any point during the year.

See also  Red Thread Grass | Dealing with Red Thread Lawn Disease Through Chemical and Cultural Control

The best way to prevent either variety of snow mold (Fusarium Patch Disease) is by keeping your garden well-watered during winter months. Maintain a consistent temperature between 50°F and 60°F . And don’t forget about mulching! Mulch helps keep moisture close to the root zone of your plants, which prevents freezing.

 Snow Mold and how to eliminate it.

Summer Patch

The symptoms of summer patch lawn disease appear in circular patches or rings, ranging from 6 inches to 3 feet in diameter. Turf within these patches is initially off-colored, prone to wilt, growing poorly, or sunken in the turf stand. Over a period of one to two weeks, the turf continues to decline, turning yellow or straw brown and eventually collapsing to the soil surface. The outer edges of the patch are usually orange or bronze when the disease is actively developing.

Affected plants are easily pulled up from the turf, and visual examination reveals that the roots, and crowns, of summer patch. Summer patch is most severe when soil pH is 6.5 or higher so thrives in slightly alkaline soil. In addition, any factors present in the soil that restrict root growth can exacerbate the disease

  • Circular yellowish dead patches up to several feet wide.
  • Roots and crowns of affected plants turn brown or black.
  • Most active during summer’s peak heat on bluegrass and fescue.
  • Slow spread from plant to plant through root contact.
  • Treat with fungicides containing fludioxonil, fluxapyroxad, or myclobutanil.
  • Reduce compaction and fertilize appropriately to prevent recurrence.

Lawn Rust

Grass rust is a fungal disease that affects your lawn when the grass’s development is impeded. It is caused by a fungal infection. Affected grasses commonly show signs of rust toward the end of summer or in early autumn (fall), particularly during times of dry periods or when the grass is deficient in nitrogen.

When your lawn is affected by Lawn Rust, it loses its vigor and becomes more prone to other illnesses and turf concerns.

Identifying the Rust is accomplished by removing a few grass blades from the affected area. The grass blades will be covered with yellowish-brown spores or dust that will be difficult to remove.

In the beginning, lawn rust appears as yellowish grass blades and little yellow/orange spots that develop into red or brown coloring as the disease moves through its stages.

Lawn rust and how to deal with it.

Take-All Root Rot

Lawn Fungus Control: - Take-All Root Rot

Take-All Root Rot is a lawn disease that results from a combination of unfavorable environmental conditions and poor grass health. Factors like inadequate lawn maintenance, improper care techniques, excessive thatch buildup, and herbicide damage can stress your grass, making it susceptible to this fungal invader.

To safeguard your lawn, prioritize cultural control methods like annual aeration and proper lawn care techniques. Chemical solutions are available for soil already infected, but they work best as part of a preventative strategy, particularly in high-risk areas. By implementing these strategies, you can maintain a lush, disease-free lawn and keep Take-All Root Rot at bay.

In-Depth Guide to Identifying and Dealing with Take-All Root Rot

With practice, you can accurately diagnose common lawn fungal diseases at a glance. Or take a sample to your local garden center for expert help.

Which Grass Species are Affected by Which Fungus

Knowing which species affects which type of grass can help with identification and the control control methods that you choose to employ to prevent their appearance.

Name of DiseaseGrass Species Affected
Summer PatchAll
Fairy RingAll
Powdery MildewAll
Pythium BlightAll
Brown PatchAll
Dollar SpotAll
Gray Snow MoldAll
Red ThreadAll
Rust DiseasesZoysia, perennial ryegrass, Kentucky bluegrass
Take-all PatchBentgrass
Leaf Spot and Melting-OutKentucky bluegrass, perennial ryegrass
AnthracnoseAnnual bluegrass, creeping bentgrass
Take-all Root RotSt. Augustine grass, Bermudagrass

As you will have noted from the above table, many of the diseases affect all grass types, with warm-season grass or cold-season grass types. However, there are some such as Rust disease that attack specific grass species.

Below is a scatter plot diagram that shows in visual terms the relationship between these common diseases and grass types.

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A scatter plot dia gram showing the diseases and the grass species they affect
A scatter plot showing the diseases and the grass species they affect

Best Fungicides for Lawns

Active Ingredients (Class)Fungicide Class, FRAC CodeProduct Name(s)
Azoxystrobin (Strobilurin)Qo Inhibitors (FRAC Code: 11)– Heritage, – Strobe 50WG
Propiconazole (Triazole)DMI Fungicides (FRAC Code: 3)– Banner MAXX II, – Fung-onil
Tebuconazole (Triazole)DMI Fungicides (FRAC Code: 3)– Fungicide 3.6, – Eagle 20EW
Myclobutanil (Triazole)DMI Fungicides (FRAC Code: 3)– Eagle 40WP, – Systhane
Fenarimol (Pyrimidine)DMI Fungicides (FRAC Code: 3)– Rubigan, – Ferbam
Trifloxystrobin (Strobilurin)Qo Inhibitors (FRAC Code: 11)– Compass, – Flint
Common Demethylation Inhibitors (DMI) used to eradicate lawn fungus problems:

Please note that specific product names may vary depending on the manufacturer and region, so it’s important to consult local resources or product labels for the most up-to-date information on available fungicides containing these active ingredients.

Once you’ve identified the particular fungus variety affecting your yard, you can choose the appropriate fungicide treatment.

Some effective over-the-counter antifungal products include:

  • Myclobutanil – Handles dollar spot, brown patch, and fusarium patch.
  • Propiconazole – Works on brown patch, rusts, leaf spot.
  • Thiophanate-methyl – Controls anthracnose, leaf spot, melting out.
  • Azoxystrobin – Effective on dollar spot, brown patch, Pythium blight.
  • Chlorothalonil – Treats brown patch, gray leaf spot, rust diseases.
  • Mancozeb – Handles dollar spot, melting out, leaf spot.

Always carefully read product labels to ensure the fungicide treats your specific lawn disease. And follow application directions carefully.

Some natural alternatives include cornmeal, neem oil, baking soda spray, or diluted hydrogen peroxide. But these generally have lower efficacy than commercial fungicides.

How to Apply Fungicide to Your Lawn

Correctly applying fungicide ensures maximum effectiveness. Here are some key tips:

  • Read and follow label directions carefully. Do not over-apply.
  • Use a backpack or hose end sprayer for even coverage over the entire lawn.
  • Mist in the early morning while the grass is damp for best absorption. Avoid watering for 24 hours after.
  • Treat the whole yard, not just infected patches, as fungi spread aggressively.
  • Apply preventatively before disease normally strikes, like spring and fall.
  • Wear gloves, goggles, a mask, and protective clothing when handling fungicides.
  • Keep pets and children off treated areas until the fungicide has fully dried.

With proper protective gear and technique, you can safely and effectively apply commercial antifungal products to your lawn.

Lawn Fungus Prevention

While fungicides treat active infections, prevention is the best long-term strategy against lawn disease. The way you mow and your lawn care practices can prevent fungi from appearing.

Maintaining the sharpness and cleanliness of your mower blades can help to avoid the spread of illness. In the event that you hire a professional lawn care company and they do not thoroughly clean their mower deck after each lawn (which is a difficult task), it is possible that they may transfer illness from one lawn to another.

Here are some additional tips:

  • Maintain proper mowing practices – Keep blades sharp, cut to the recommended height, and disinfect mower regularly.
  • Water early – Water deeply 2-3 times a week in the early morning to avoid lingering moisture.
  • Improve airflow – Prune trees/shrubs to open up air movement over the lawn.
  • Fertilize appropriately – Use a balanced nitrogen-rich fertilizer to build turf health.
  • Reduce thatch buildup – Dethatch in spring and fall to prevent fungus-friendly conditions.
  • Seed with resistant varieties – Choose fungal-resistant grass types when overseeding.
  • Allow proper drying time – Let the lawn dry fully between watering/rain before mowing.
  • Treat acidity – Test pH regularly and apply lime if needed to reduce acidity that encourages fungi.

With vigilant lawn care practices, you can avoid many of the factors that allow fungal diseases to gain a foothold.

When to Call a Professional

In most cases, home treatment can successfully banish common lawn fungi. But more advanced infestations may require calling in a professional:

  • If over 50% of the lawn is affected
  • For a rapid-spreading disease like pythium blight
  • If the disease continues to spread after multiple fungicide applications
  • For lawn replacement if turf is extensively damaged

A lawn care specialist has industrial-strength fungicides and application equipment plus the expertise to fully eradicate severe lawn fungal diseases.

Final Thoughts – Lawn Fungus Control

The unfortunate reality is that lawn disease often begins to spread before homeowners are aware of it, and as a result, they exacerbate the situation.

Given the seriousness of a few of these lawn fungi, it is preferable to look to employ a preventative strategy rather than waiting for them to manifest themselves and wreak havoc on your lawn’s health.

With vigilance and prompt treatment, you can keep lawn fungi at bay for a healthy, lush yard all season long.

Commonly Asked Questions About Lawn Fungus Control

What does lawn fungus look like?

Lawn fungus appears as discolored, dead patches ranging from small spots to areas several feet across. Common symptoms include yellowing, browning, low growth, and blighted areas. Fungal growth may appear cottony or powdery.

When is lawn fungus most active?

Fungi thrive in warm, humid conditions. Most fungal diseases peak in early fall and late spring. Wet weather encourages outbreaks anytime in summer. Snow molds occur in winter.

How do you treat lawn fungus naturally?

Natural antifungal options include spraying diluted hydrogen peroxide, applying cornmeal, using neem oil, and treating with baking soda mixed with a small amount of liquid soap. Results are generally less effective than commercial fungicides.

How long does it take for fungus to kill grass?

If left untreated, aggressive fungal diseases like pythium blight can damage or kill turfgrass in as little as two weeks. More common fungi may take 4-6 weeks to significantly thin and damage a lawn. Early intervention is key.

Should I bag clippings if my lawn has a fungus?

Bagging clippings from an affected lawn can help prevent spread. But ensure the mower deck is disinfected after use on diseased grass since fungal spores collect there. Proper mower cleaning is more effective than bagging.

How often should you treat lawn fungus?

Depending on the product used, treatment should be repeated every 7-14 days until fungus is under control. Preventative applications can be made every 3-4 weeks during peak disease seasons. Always follow fungicide label directions.

What is the best time of day to treat lawn fungus?

The optimal time to treat is early morning while grass blades are still damp but before temperatures rise. This allows the maximum absorption and effectiveness of the fungicide application.

How long after treating fungus can I mow?

It’s best to wait at least 24 hours after fungicide treatment before mowing to allow full absorption into the grass. Some product labels may specify longer wait times, so always check directions.

How long after applying fungicide can I water?

Avoid watering for 24 hours after fungicide application for best results. Some products are “watered in” as part of treatment, so read the label. Overly wet conditions after application can wash away effectiveness.

How often should you apply fungicide as a preventative?

For preventative treatment before fungal disease normally strikes, reapply fungicides every 3-4 weeks. Heavier disease pressure may require more frequent applications per product guidelines. Rotate between treatment modes.

Resources

  1. Pennsylvania State University: Turfgrass Diseases: Summer patch (Causal fungus: Magnaporthiopsis poae)
Keith Hardy - Bio Photo
Keith HardySenior Editor

Keith has been involved in the gardening and landscaping industry for the past 21 years. From a jobbing gardener to running his own landscaping services. He is now dedicated to bringing you the latest in gardening news. Read more

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