lawn fungicide in fall

Lawn Fungicide: Treat and Prevent Fungal Diseases in Your Lawn

Even the best cared for lawns can develop a fungal problem, which present not only as mushrooms, but also as brown patches, yellow spots, rings of dead grass, or even nondescript slimy areas. Fungi and their spores occur naturally, and while found nearly everywhere, rarely cause lawn issues unless they reproduce too rapidly. Fortunately, preventative lawn care and fungicide treatments can help control disease and keep your lawn healthy.

In this article:

  • What Causes Fungus in Lawns? 
  • What are Fungicides? 
  • How to Choose the Best Lawn Fungicide
  • Common Grass Diseases Fungicides Treat
  • When to Apply Fungicides
  • How to Apply Fungicides
  • Tips to Prevent Fungal Diseases

What Causes Fungus in Lawns?

Disease-causing fungi are almost always present in the soil, waiting for favorable conditions. Specific environmental factors, such as the humidity of a region or an especially rainy season, can increase the risk of a fungal outbreak in a lawn.

 Other potential causes include improper lawn care, such as over-fertilization, overwatering, growing a grass variety that is poorly suited to the area, or mowing the lawn too short.

lawn fungi that needs to be treated with lawn fungicide

What are Fungicides?

Fungicides are used to control or prevent fungal diseases. Lawn fungicides are made with chemical compounds or biological organisms that kill parasitic fungi and/or their spores. Typically, lawn fungicides will not affect weeds or desirable plants.

How to Choose the Best Lawn Fungicide

With more than two million different species of fungi, determining which exact species is causing a lawn issue may not always be possible, but understanding the different types of fungicides is an important step in choose the best one for your unique needs. Lawn fungicides can be classified as preventive or curative, contact or systemic, and broad- or narrow-spectrum. Let’s take a closer look at the differences between these classifications.

Preventative vs Curative

Some lawn fungicides are preventative, designed to keep healthy lawns healthy. Others are formulated to stop active fungal infestations. It is important to understand that all fungicides are preventative, but not all fungicides are curative. Deciding which fungicide to use for your lawn will depend on whether there is an active fungal infestation or whether you simply want to reduce the likelihood of one occurring.

  • Preventative Fungicides
    Preventative fungicides are applied to a lawn before fungal problems arise to create an environment where fungus spores as not likely to survive and reproduce. 

  • Curative Fungicides
    Curative fungicides kill existing fungus issues and offers preventative protection for grass.

Pro Tip
It is best to routinely use a preventative fungicide rather than wait to treat an active infestation. While a curative fungicide will kill an existing fungus, it will not repair the damaged lawn.

Contact vs. Systemic

While all lawn fungicides either kill existing fungi or prevent them, they do so differently, depending on the product.

  • Contact Fungicides
    Contact fungicides are preventative only. When applied, they adhere to the surface of grass blades and form a protective barrier, prohibiting fungi from reproducing. Contact fungicides do not last as long or provide as much protection as systemic products.

  • Systemic Fungicides
    Systemic fungicides are absorbed into the blades of the grass and then traves through the leaves to kill fungi internally and prevent new infestations.

Broad-Spectrum vs. Narrow-Spectrum

Lawn fungicides are also classified as broad- or narrow-spectrum.

  • Broad-Spectrum Fungicide
    Broad-spectrum fungicides work to kill or prevent a wide variety fungal species. Since there are so many types of fungi that can infect lawns, many fungicides are broad-spectrum.

  • Narrow-Spectrum Fungicide
    Narrow-spectrum fungicides only treat one or two fungal diseases. Users should know exactly which type of fungal disease ails their lawn before using a narrow-spectrum fungicide. However, narrow-spectrum fungicides are highly effective against the specific species of fungus they are designed to treat, and they are less likely to kill beneficial organisms that help increase nutrient uptake in your lawn.

Common Grass Diseases Fungicides Treat

Brown Patch/Large patch

Brown patch or large patch is one of the most common diseases affecting grass in the South. Fungus called rhizoctonia manifests as large patch in warm season grasses and brown patch in cool season grasses.

Warm season varieties like Bermuda, zoysia and centipede are particularly vulnerable when vigorous summer growth slows for the transition into dormancy.

Brown patches on lawn

Dollar Spot

Dollar spot is a white, web-like fungus that branches out from one blade to the next, infecting the grass in small round spots. This fungus secretes toxins that cause white lesions on the grass blades, multiplying and expanding until the green color disappears from the blade completely.

Unfortunately, dollar spot does not die during winter, but persists season to season. It spreads most readily when temperatures fall between 60 and 85 degrees.

The disease may spread inadvertently when people, animals, equipment, water or wind move infected leaf debris from one area to another.

dollar spot fungus on lawn

Take-All Root Rot

Take-all root rot is a fungal disease that causes weak, brown, dead patches in lawns. It typically occurs in wet conditions and is more severe in less fertile and sandy soils. Take-all root rot lives in thatch, a brown layer of mainly dead grass that accumulates in some lawns between the green grass blades and the soil surface.

 Mowing or foot traffic do not usually cause the spread of this disease, but spreading occurs when infected grass, thatch, or soil is moved from one location to another. This disease commonly appears in spring or early summer when grass comes out of winter dormancy.

Fairy Rings

Fairy rings appear as brown or green circles or as rings of mushrooms that vary in size from a few inches to several feet in diameter. Fairy rings typically occur in the summer.

The fungus that causes fairy rings doesn’t attack grass directly but causes damage by affecting the soil as it feeds on decaying organic matter in the thatch layer or in the soil from rotting tree roots, stumps and buried lumber scraps.

The fungi spread through spores carried by wind or water. Fairy rings often develop in poor soils or in heavy thatch, proving particularly troublesome in sandy soils.


Rust diseases present as orange rust-like flecks on grass blades. Rust diseases occur in early spring through mid-summer and prefer moist, low-light areas.

Leaf Spot

Leaf spot begins with spots on grass blades that may have yellow or purple boarders. The lower leaves of the infected plant shrivel which causes severe thinning of the lawn. Several small spots may converge into one large spot. Leaf spot is often seen in the cool, wet weather of spring.

Red Thread

Red thread disease symptoms appear as patches of turf with a red or pink hue. Red thread is commonly seen during humid, rainy period of late spring and early summer and is associated with lawns that do not receive adequate amounts of nitrogen fertilizer.

When to Apply Fungicides

Fungicide should be applied as soon as a problem is noticed. Prompt treatment helps keep the fungal disease from spreading to other parts of the lawn. For a more preventative approach, applying fungicide throughout the late spring and summer months (or when nightly temperatures rise above 60 degrees) can play a key role in the health of your lawn.

Often commercial landscapers and golf course superintendents use disease forecasting systems that consider local temperature, relative humidity, and leaf wetness to help determine when fungicides need to be applied. Local extension offices can be a great resource in helping homeowners forecast when to use fungicides.

How often fungicide is applied to the lawn will depend on the product used. Some fungicides are reapplied every few weeks, while others can last up to 4 weeks. Follow the manufacturer’s recommendations.

How to Apply Fungicides

Lawn fungicides come in a variety of application methods, such as ready-to-use spray, concentrated liquid, and spreadable granules. No matter which application method you choose, always read and follow the manufacturer instructions carefully. Wear gloves, face mask, long sleeves, and long pants when applying fungicide.

Antifungal products used for lawns are typically safe for all varieties of grass, and do not cause damage to other plants or weeds.

To prevent fungicide resistance in lawns, be sure to rotate the type of fungicide every few applications. Using the same  awn fungicide with the same active ingredient too frequently can cause the fungus to develop a resistance, rendering the fungicide ineffective.

Pro Tip
For best results, wait two weeks after using a lawn fungicide before overseeding to give new seeds the best possible protection from fungal disease.

Prevention: Tips to Prevent Fungal Diseases

  • Avoid nitrogen fertilizers after July 15 for warm season grasses
  • Mow regularly, but avoid mowing below the recommended height for your grass variety
  • Remove excess thatch when deeper than one inch
  • Aerate your lawn once per year
  • Water in the early morning before the dew dries and avoid overwatering
  • Consider thinning the tree canopy in problem areas with dense shade

Accurate Diagnosis is Key

The key to treating lawn diseases is an accurate diagnosis. Without knowing precisely which disease is affecting your lawn, it’s difficult to be certain which option will work best to correct the issue.  Few fungicide options are available to homeowners, so if you suspect fungal disease, contacting a lawn professional for treatment may be your best option.

If you have additional questions about lawn fungicides or suspect fungal issues in your lawn, our Certified Turfgrass Professionals at NG Turf are happy to answer any questions you may have. Give us a call at 770-832-8608 or email


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