A Complete Guide on Identifying, Fighting and Preventing Lawn Diseases

Bright red spots and patches of red thread in perennial ryegrass

While weeds and pests often take center stage in our lawn care efforts, it's important not to overlook the potential damage caused by other organisms — like fungi.

Among these organisms, fungi reign supreme as the most common parasites responsible for plant diseases. The key to preventing the infestation of weeds, pests, and fungi lies in consistent lawn management and care. By cultivating a healthy and robust lawn, you significantly reduce the risk of fungal invasions in your turf. It's worth noting that fungi spores naturally inhabit our lawns without causing harm. But, under certain conditions, these spores can germinate and give rise to diseases such as Red Thread and Brown Patch, ruining the seamless look of your golf course lawn. 

Lawn disease identification is an important first step in learning about the types of lawn diseases and how best to control them. From there, you can move on to lawn disease treatment and preventative measures. Armed with this knowledge, you'll be well-equipped to tackle any fungal challenges that threaten the health of your pristine lawn.

What Are Lawn Diseases? 

With over 2-11 million estimated species of fungi in the world, there’s only a fraction we know about. Fortunately, there are a few offenders which crop up in lawns quite regularly; you just need to learn how to identify them. 

But first, let’s answer an essential question. What are lawn diseases? Lawn diseases are a range of fungal, bacterial, or viral infections that can affect the health, appearance, and vitality of your lawn. These diseases can cause various symptoms, such as discoloration, thinning, wilting, patchy areas, or the death of grass blades.

What Causes Lawn Diseases?

Lawn diseases can be caused by various factors, including improper watering, compacted soil, incorrect mowing practices, excessive fertilizer use, and certain weather conditions. For long-term prevention, it’s worth considering if any of these factors apply to your lawn: 

Underwatering or overwatering your lawn

One of the primary culprits behind lawn diseases is improper watering. Both underwatering and overwatering can create conditions that promote the growth of fungi. Consistently monitoring and adjusting your watering practices based on the specific needs of your grass can help prevent disease development.

Compacted soil

Soil compaction restricts the flow of air, water, and nutrients to the grass roots, making the lawn more susceptible to diseases. Core aerating the soil is a good solution to alleviate compaction. This process involves punching small holes into the soil to facilitate proper air circulation, water absorption, and nutrient penetration down to the roots. Most core aerators space the holes 2 - 3” apart.

Improper mowing practices

Cutting the grass too long or too short can weaken the lawn and make it susceptible to diseases. To maintain optimal lawn height, mow the grass regularly, ideally two times a week. Follow the "one-third rule" by cutting off no more than one-third of the grass' total length at each mowing session. This promotes healthy growth and reduces stress on the grass. Ensuring your mower is sharp is also critical to preventing lawn diseases.

Excessive fertilizer use

While fertilizers are beneficial for lawn health, overdoing it can have adverse effects. Excess fertilizer can encourage the growth of weeds and fungi alongside your grass, creating an imbalance in the lawn ecosystem. Following proper fertilization guidelines and avoiding excessive application will help maintain a healthy balance in your lawn. Lawn fertilization is definitely a case where more isn’t necessarily better.

Weather conditions

Certain weather conditions, such as high humidity and cold, damp environments, can create an ideal breeding ground for fungi. These conditions provide the moisture and temperature necessary for fungal growth. Regular monitoring during periods like the fall and winter, plus implementing preventive measures, like fungicide applications, can help mitigate the risk of lawn diseases.

While taking proactive steps can minimize the occurrence of lawn diseases, it's important to be prepared for potential outbreaks. Before initiating treatment, correctly identifying the specific lawn fungus is crucial. In the following sections, we will explore common lawn fungi, their distinguishing characteristics, and the most effective fungicides available for treating them.

Types of Lawn Diseases

From Brown Patch and Dollar Spot to distinct Red Thread and Rust, we will shed light on each lawn disease's distinct symptoms, triggers, and preferred environmental conditions. Spot the warning signs early on, enabling you to take measures to address the issue before it escalates. We’ll also discuss effective treatment methods, including fungicides, and other targeted approaches, to help you combat and manage specific lawn diseases effectively.

Related: The Most Effective Fungicides to Use on Your Lawn.


Lawn Disease Identification

Brown Patch

Appearance: Keep an eye out for circular patches of dead, sunken grass varying in size, ranging from a few inches to several feet in diameter. During periods of high humidity, the perimeter of these circles will exhibit a light gray appearance.

Preferred conditions: Brown Patch tends to thrive during warm or hot weather conditions, particularly in the spring and fall. Factors such as wet leaves, excessive moisture, and over-fertilization contribute to the spread of this disease.


Dollar Spot

Appearance: This lawn disease is characterized by small, silver dollar-size circles that can expand up to six inches in width. Over time, these circles may form larger blocks, and your grass will exhibit yellow spots with a distinct brown border, giving them a water-soaked appearance. Under bright lighting conditions, you might see cobweb-like growth.

Preferred conditions: Dollar Spot disease occurs from late spring to fall, preferring mild-to-warm temperatures. It thrives in both excessive and insufficient moisture conditions, and under-fertilization increases susceptibility.


Red Thread

Appearance: Red or bleached-looking patches begin to form. An unmistakable sign of the disease is the binding of grass blades by reddish-pink threads accompanied by the appearance of red spores on your shoes or tools.

Preferred conditions: Red Thread lawn disease thrives during the mild temperatures of early spring and is particularly fond of damp conditions. Under-fertilizing, inadequate air circulation, shade, excessive thatch, and compacted soil are all favored conditions too.



Appearance: Irregular patches of thinning grass that turn from yellow specks to rust-colored blades. A distinctive characteristic of this disease is the presence of orange spores that cover the grass blades. Similar to Red Thread disease, you will begin to observe these spores on your tools, shoes, and mower. 

Preferred conditions: Most likely to occur during moderately warm or mild temperatures, like early summer and fall. Rust enjoys drought, hot weather, excessive moisture, excessive shade, and under-fertilization as its preferred conditions.


Snow Mold

Appearance: Starts with small, circular pinkish spots, which can expand up to a foot in length. Grass blades become saturated with water, especially underneath snow cover, resulting in a red-brown discoloration. In the morning light, the presence of white fungal threads becomes visible.

Preferred conditions: Typically emerges during winter. This disease is favored by moist conditions like poor drainage and excessive shade. Over-fertilization, particularly with nitrogen-rich fertilizers, can increase your turf’s risk of Snow Mold.


Pythium Blight

Appearance: This is cotton candy-like in appearance, made up of white, fluffy fungal threads that develop on turfgrass after blades have turned a dark-green or purple color. Growth is most pronounced when the infected leaves are wet, such as in the morning following a night of rain or heavy dew. Grass blades feel slimy or greasy.

Preferred conditions: Periods of warm and humid weather, specifically when the leaves of the turfgrass remain wet for a minimum of 12 hours.


Leaf Spot

Appearance: Small brown spots on grass blades. Over time, these spots expand, acquiring dark purplish or reddish-brown oval borders with tan centers. As the disease progresses, the infected leaves turn yellow and deteriorate.

Preferred conditions: Leaf Spot thrives under conditions like mowing the grass too short, providing light and frequent watering, and using too much nitrogen fertilizer in the early spring. Turfgrasses that lack nitrogen are more susceptible to these diseases.


Necrotic Ring Spot

Appearance: Initially, light green to straw-colored spots or patches develop in the lawn. As the disease progresses, the grass at the patch margin dies and becomes matted, while the grass inside the ring remains healthy and green, creating a doughnut or frog eye pattern.

Preferred conditions: Circular patches of infected turf typically develop during cool and wet weather. Spring and fall are the favored conditions. High temperatures and drought stress can intensify the symptoms, making them more apparent and noticeable.


Powdery Mildew

Appearance: Affected turf appears white or light gray in color. Small pustules grow on grass blades. These pustules contain clusters of white spores that may eventually cover the entire leaf surface.

Preferred conditions: Powdery Mildew commonly affects slow-growing turf, especially in shaded areas. It tends to thrive in cool and cloudy conditions that are typical in spring and fall. High humidity can also promote its development. The first signs of Powdery Mildew usually appear in areas with limited air circulation. Using excessive nitrogen fertilizer can also increase the risk of infection.


Slime Mold

Appearance: You may notice spore masses of different colors, such as white, gray, brown, purple, or black, suddenly appearing on the grass blades. They can temporarily cause slight yellowing of the turf blades by blocking photosynthesis.

Preferred conditions:
Slime Mold likes warm weather and lots of moisture. These conditions create an ideal environment for growth and infestation.


Lawn Disease Treatment

Once you’ve identified the type of lawn disease infesting your grass, you can move on to different control methods and treatments. Despite hard labor to maintain your lawn, fungal diseases can strike suddenly and quickly. Let’s take a look at the best fungicide products to use for effective and targeted lawn disease treatments.

Caravan G — Insecticide and Fungicide 

Caravan G is a highly recommended fungicide and insecticide for addressing pest problems and preventing fungal issues in your lawn. This granular product offers exceptional control of both insects and fungi in just one application. It contains two active ingredients, azoxystrobin, and thiamethoxam, which effectively target pests like grubs, craneflies, chinch bugs, and more. Caravan G is also capable of controlling lawn fungi such as Brown Patch, Fairy Ring, and Large Patch.

With Caravan G, you can enjoy season-long grub control and a month of preventive control against Large Patch disease. By combining both insecticide and fungicide properties, this product proves to be cost-effective compared to using two separate treatments, saving you both time and money. 

Headway G — Fungicide Granular

Headway G is an exceptional granular fungicide that offers broad coverage against various common lawn fungi. With a single application, it effectively targets and mitigates issues caused by Brown Patch, Dollar Spot, Fairy Ring, and more. 

What sets Headway G apart is its unique formulation, combining two broad-spectrum fungicides that work synergistically to eliminate a wide range of lawn fungi. This comprehensive coverage would typically require the use of multiple products, but with Headway G, you get all the benefits in one. Its all-in-one formulation simplifies the treatment process and ensures efficient control of various lawn fungi, providing a convenient and cost-effective solution for your lawn care needs.


Pillar SC — Liquid Fungicide

Pillar SC Liquid Fungicide is the perfect solution when you need fast and effective disease control for your lawn. This liquid fungicide acts quickly, providing exceptional control against 26 common turfgrass diseases, including Brown Patch and Dollar Spot. It is safe to use on all grass types, ensuring compatibility with your specific lawn needs. To achieve the best results, it is recommended to apply Pillar SC using a backpack sprayer with the appropriate spray tip while wearing the necessary protective clothing, eyewear, and gloves.



Fungicide Application Tips

When applying fungicides to your lawn, whether in liquid or granular form, it's essential to follow proper application techniques for effective disease control.

For liquid fungicides, carefully read and follow the instructions on the label. Use a high-quality sprayer and calibrate it according to the manufacturer's guidelines. Apply the fungicide in good weather conditions, and avoid windy days. Walk at a steady pace, overlapping each pass, to achieve uniform coverage across your lawn.

As for granular fungicides, again, read and follow the instructions provided. Use a broadcast spreader calibrated to distribute the granules evenly. Walk in straight lines, overlapping each pass, for complete coverage. After application, lightly sweep or water the lawn to help the granules settle. Apply granular fungicides when the grass and soil are dry.. For best results, water in liquid and granular fungicide within 24 hours of application.

In both cases, wear protective clothing, eyewear, and gloves during application. 

Preventative Lawn Disease Control

To effectively control lawn diseases, it is important to adopt a comprehensive approach that addresses the underlying causes and prevents further spread before using fungicides — this involves maintaining proper lawn care practices such as promoting air circulation, watering wisely, and practising proper fertilization. By following these strategies and maintaining a healthy lawn, you can minimize the impact of diseases and enjoy a vibrant, disease-free golf course lawn. 

Get clued up on all the lawn care terminology by checking out our lawn care glossary.