Lawn Fungus Control | 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....

A lawn fungus is a plant 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 that understanding what can cause a fungus and how to control and eradicate it to ensure a healthy good looking lawn.

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.

We will look at the factors that cause and influence the spread of grass fungi as well as examining the most common type of fungi that affect lawns together with various treatments available to eradicate the problem and prevent it happening again.

How to Identify Various Lawn Diseases

How to Identify Various Lawn Diseases

A lot of people don’t realize what they’re looking at when they see brown or discolored spots on their lawn that they actually have a fungus problem. The discoloration comes from fungus spores or from chlorophyll in the grass. Chlorophyll turns green when it absorbs light. When there’s not enough light, the chlorophyll takes on a brownish hue.

The key to dealing with lawn fungus is to know what you are up against so that you can employ the correct treatments. Different fungi have different scarring characteristics. Know what these are enable you to quickly identify the disease and employ the appropriate lawn fungus control measures.

Critical Lawn Disease Facts and How Lawn Fungus Control Works

Lawn fungus control involves treating the soil around the base of the plant with fungicides. This helps prevent the disease from spreading into healthy plants. It may also involve removing infected turf with a mower.

Causes of Lawn Disease

The most common cause of lawn disease is Fusarium wilt. It’s caused by a fungal infection that spreads through the soil. It affects many types of grasses, but not all.

1. The Effect of High Nighttime Temperatures

Lawns will die if nighttime temperatures rise above 85 degrees Fahrenheit . This includes warm nights after a rainstorm or thunderstorms. If you live in a humid climate like some southern US states, this may happen frequently during the summer months.

2. Humidity and Lawns

High humidity can be a consequence of high temperatures, another factor that can encourage turf disease. This is because high levels of humidity keeps the lawn damp, and lawn fungus thrives in that dark, warm, wet environment. 

3. Reduced Air Flow Over Lawns

Having a garden that is protected from the wind  by bordering trees or fencing you may be at greater risk of developing grass fungal issues, particularly in warmer temperatures.

Lawn fungal issues are substantially reduced when there is enough air movement. You can help keep grass disease problems to a minimum, even during periods of high humidity if you can increase air movement across the surface of your lawn as this will help reduce or eliminate excess moisture.

Types of Lawn Fungus

Pythium insidiosum | Pythium Blight

Pythium Blight Disease Cycle

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 in wide but may expand rapidly to cover large areas. Affected areas may be uneven, characterised by bare patches or thinning turf. Affected areas may be muddy, with standing water. The grass may appear yellow or straw coloured, with wilting or loss of grass color.

For a more detailed look at Pythium blight and how to eliminate it, click here.

Brown Patch

Lawn Fungus Control  -brown spot

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 lawn like golf courses.

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

For a more detailed look at brown patch and how to prevent and eliminate it, click here.

Red Thread

Lawn fungal diseases - 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.

For a more detailed look at Red Thread and how to eliminate it, click here.

Snow Mold

Snow mold diseases come in two varieties gray and pink snow mold (fusarium patch). Unfortunately they are fairly common lawn diseases that appears 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.

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.

For a more detailed look at Snow Mold and how to eliminate it, click here.

Summer Patch

Summer patch lawn disease is also known as Sod Webworm. A Sod Webworm is a moth caterpillar that attacks grass. The adult moth lays its eggs in the lawn, and the larva eats the grass roots. The larva often tunnels through the soil, leaving trails of web-like tunnels.

Lawn Rust

How to Identify Grass Rust Fungi - Lawn Fungus Control

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 vigour and becomes more prone to other illnesses and turf concerns.

Identifying the Rust is accomplished by removing a few bladed of 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 colouring as the disease moves through its stages. A more detailed explanation of lawn rust and how to combat it can be found here.

Dollar Spot

Lawn Fungus Control - dollar spot

Dollar spot lawn disease is 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 fungi 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 seed, 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.

A more detailed explanation of dollar spot fungus and how to combat it can be found here.

What are the Best Fungicides for Lawns?

The best fungicide for lawns will depend on what type of fungus is causing problems. If it’s powdery mildew, then a copper based product may be effective. If it’s leaf spot, then a sulfur based product might be better.

Tips for Applying Fungus Treatments for Lawns

For lawns, I recommend applying a sulfur based product first, followed by a copper based product. It should take at least two applications before you see any results.

Often fungi survive and thrive because of lack of nitrogen in the soil. One effective method of removing many fungi is to regularly fertilize your lawn with a nitrogen rich fertilizer.

Lawn Fungus Control: Preventing Lawn Fungus Taking Hold in the First Place

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.

It is possible that the habits of watering and mowing will have a significant influence on illness in the long run.

For starters, it is advised that you water your grass first thing in the morning so that the sun has time to dry up your lawn. When you water your lawn in the evening, the water lingers on the grass and produces an environment that is conducive to fungus development.

The way you mow makes a difference as well. 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.

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 lawns health.

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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