13 Grass Diseases You Need to Watch For

Serene suburban home with picturesque white facade, black shutters, manicured lawn, white picket fence under clear blue sky - aware of grass disease.

Grass diseases can ravage your lawn if you don’t take the steps to treat it. If your garden looks patchy or discolored, it may be time to start treating the impacted area. Read on to learn the thirteen most common lawn diseases in the US and how to identify them. We’ll also cover how you can treat your grass so it can thrive.

What Are Grass Diseases?

Unfortunately, grass diseases are common in the USA. Whether your lawn will be affected depends on the climate, soil, species, and how you maintain your garden. The disease manifests in symptoms like discoloration, wilting, and the eventual death of your lawn.

Pathogens like fungi and bacteria attack the grass and spread if left untreated. Managing and preventing diseases typically involves properly irrigating and fertilizing your lawn and treating infected areas with fungicides to prevent the spread.

Green grass showcasing nature's vibrant shades, while staying vigilant against grass disease.

How Can You Spot Grass Disease?

Spotting diseases in your grass is akin to recognizing when your lawn isn’t in its best shape. Here’s how you can identify the signs:

  • Changes in Color – If you notice patches of grass that differ in color from the rest, like turning brown or yellow, it might indicate your lawn is diseased.
  • Texture Differences – Take note of whether the grass feels different than usual. If diseased, it may sometimes feel slimy, mushy, dry, and brittle.
  • Irregular Patches—Look for irregular patches or spots on the grass. They may show discoloration or unusual growth.
  • Areas with Thinning Grass – Dead spots or areas where the grass is thinning out could be a sign of disease, especially if they spread over time. For easy weed removal and garden maintenance, consider having a weed tool on hand.
  • Fuzzy Growth – Some diseases cause fuzzy or powdery growth on the grass blades or soil surface. Keep an eye out for any unusual textures.
  • Unpleasant Smells – Certain diseases create unpleasant odors. If you detect an odd smell coming from your lawn, it might be a sign of disease.

Regularly watching your lawn to spot signs of disease early on can help you address issues quickly and stop the spread.

Scattered dry leaves hinting at autumn on green grass field, prioritizing grass disease prevention.

13 Grass Diseases to Look Out For

Here are the thirteen most common grass diseases and how to spot them in your garden. Being aware of early issues can help stop the spread before it gets out of hand.

St Augustine Grass Diseases

St. Augustine grass diseases are common – especially in the hotter months. The most common disease for this type of lawn is the St. Augustine Decline (SAD).

SAD happens because of the panicum mosaic virus and causes yellow, thinning leaves. Unfortunately, there is no cure. Replacing infected grass and keeping a tidy garden are the only ways of preventing the disease from spreading. It is also essential to clean your mower’s blades after each cut to prevent further spread of this disease.

Rust Diseases in Grass

Rust disease in grass causes orange or brown spots on the blades, eventually leading to yellowing and wilting. If left untreated, the grass will eventually die.

Rust disease occurs when fungal pathogens from the Puccinia genus infect the grass. This is more common in warm and humid environments, typically during late summer and fall.

Rust disease is often worse when you water your grass incorrectly and there is inadequate drainage or there is too much nitrogen in the soil.

Red Thread Grass Disease

Pink or red thread-like strands on grass blades could indicate that red thread grass disease is present. This happens when your grass is infected by the fungal infection called Laetisaria fuciformis.

Red thread usually happens in cool grass seasons, when the soil has too much moisture and an inadequate balance of nutrients. The diseased area can worsen if you overwater or cut the grass with a blunt blade.

Microdochium Patch (Fusarium)

Microdochium patch, or Fusarium patch, causes patches on the grass that change in color from orange-red to grey, especially in cool and damp weather.

The fungus known as Microdochium nivale causes this disease. Cool-season grasses like ryegrass and fescue are more commonly found to have fusarium. It flourishes in temperatures ranging from 40°F to 60°F. Look out for orange-red patches on your grass during the winter months.

Prolonged moisture and high humidity can also help Microdochium to thrive. To counteract this, ensure your soil is draining properly, and there isn’t any evidence of thatch buildup. It is also essential to check the soil’s pH level, as high levels of nitrogen along with low levels of phosphorous and potassium will make this condition worse.

Brown Patch

Brown patch causes circular brown areas, which causes lifeless grass blades to form. This usually happens in hot and humid climates with too much thatch and nitrogen in the soil.

This disease happens when the Rhizoctonia solani fungus flourishes in temperatures above 85°F alongside high humidity.

Excessively fertilizing your lawn or poor drainage methods can make your grass more susceptible to brown patches. In warm seasons, St. Augustine grass and zoysia grass are particularly vulnerable.

Dollar Spot

Dollar spot leaves pale straw color spots on grass leaves, eventually creating patches of dead grass the size of a coin. Over time, these coin-size patches will emerge into larger, irregular shapes. This typically occurs in warm and humid conditions and in poor draining soil that lacks adequate nutrients.

The fungus Sclerotinia homoeocarpa causes dollar spots and usually affects grass that prefers cooler conditions, like bentgrass and perennial ryegrass.

Fairy Ring

Dark green grass encircles patches of dead grass in sandy soil with low nitrogen levels, creating a fairy ring. These rings happen because of different fungi in the soil, particularly the Basidiomycetes species.

Factors like organic matter breakdown, soil compaction and watering habits affect the growth of fairy rings. In turfgrass, excessive thatch and poor soil drainage can cause fairy rings to spread.

Vibrant green grass with morning dew at dawn, aware of grass disease.

Leaf Blight

Leaf blight causes stretched water-soaked spots on the leaves of grass, causing them to change in color to yellow or brown. This typically occurs in cool-season grasses when the weather is humid.

Types of fungal pathogens like Rhizoctonia and Bipolaris cause this disease.  Warm temperatures, high humidity and wet leaves also help leaf blight take hold. To counteract this, ensure you use proper mowing techniques and that the turf isn’t too thick.

Grey Leaf Spot

Grey leaf spot creates round light brown spots on blades of grass, especially in regions with warm and rainy weather.

This condition is triggered by the fungus Pyricularia grisea. It typically impacts grass types like St. Augustine grass and Bermuda grass, which thrive in warmer temperatures.

Grey leaf spot tends to spread when temperatures range from 75°F to 90°F, and there’s high humidity in the air. Wet leaves and too much fertilizer can also help grey leaf spots take hold.

Necrotic Ring Spot

Necrotic ring spots form round areas of grass that have died. You’ll typically see a brownish-yellow circle in cool-season grass types, which indicates its presence.

Ring spots occur when different types of fungi like Ophiosphaerella and Leptosphaeria infect the area. Too much thatch, poor soil aeration and nitrogen imbalance can contribute to its development.

Powdery Mildew

Powdery mildew appears as a white or grey powdery layer on grass blades, typically in cool and damp weather conditions.

Fungal pathogens belonging to the Erysiphales order, like Blumeria graminis are the main causes of powdery mildew.

This disease thrives in temperatures ranging from 60°F to 80°F, along with high humidity and restricted airflow. If your turf is dense or subject to shade, it can encourage powdery mildew to grow.


Pythium causes grass blades to appear greasy and waterlogged, causing them to droop and wither quickly. This happens when the soil doesn’t drain properly, and in warm and moist weather conditions.

This disease occurs when different types of pythium impact the grass during cold and warm seasons.

Too much water, compacted soil, and inadequate drainage typically cause Pythium blight. High nitrogen levels in the soil and excessive thatch can also worsen Pythium outbreaks.

Slime Mold

Slime mold presents itself as powdery growth on grass blades during wet and humid conditions. A fungus found in the Myxomycetes group feeds on the organic material found in soil. This disease thrives in moist conditions and high temperatures when organic matter is more likely to decompose in the soil.

While slime mold doesn’t directly damage lawns, it can be unattractive to look at.

Man operating lawn mower for neat suburban lawn, attentive to grass disease.

How to Treat Grass Diseases

To keep your lawn thriving, it’s important to address grass diseases quickly. Below are steps you can follow to tackle the spread of lawn infection:

Identify the Disease – Before treating the disease, figure out the specific type that’s affecting your lawn using our guide.

Follow Best Lawn Practices – Implement good lawn care practices to prevent the disease from spreading any further. Regularly mow, use the correct watering techniques, and use the right fertilizer.

Use Fungicides – Depending on the seriousness of the disease, you may need to use fungicides to control the spread. Use a fungicide for the disease ravaging your lawn and follow the instructions carefully for best results.

Remove Infected Areas – If certain parts of your lawn have been badly damaged, consider replacing them with healthy turf by reseeding to stop the spread.

Improve Drainage – Ensure proper drainage in your lawn to avoid waterlogged conditions that can worsen the disease.

Adjust Irrigation Practices – Be mindful of overwatering as it can contribute to certain grass disease development and spread. Make sure to adjust your watering schedule to give your lawn just the right amount of water it needs, avoiding excessive moisture that could lead to the growth of diseases.

Summing Up

Maintaining a vibrant lawn requires careful attention and quick action to tackle grass diseases. By learning about the signs and symptoms in this guide, you can spot potential problems early and take measures to deal with them.

Acting early is crucial in preventing diseases from spreading and preserving the beauty of your garden. With a little dedication and effort, you can enjoy a beautiful lawn all year round.

Suburban brick house, manicured lawn, paved walkway, palm tree on sunny day, with caution towards grass disease.

Frequently Asked Questions

Our most frequently asked questions about grass diseases you need to watch.

1. What Are the Reasons Behind Grass Diseases?

Grass diseases happen because of pathogens like fungi and bacteria that invade the grass, especially in conditions that speed up their growth.

2. How Can I Determine if My Lawn Is Infected With a Disease?

Keep an eye out for signs like color changes, differences in texture, irregular patches, thinning grass, fuzzy growth and unpleasant smells coming from your lawn.

3. Is It Possible To Treat All Grass Diseases?

While you can manage many grass diseases fairly easily, some can be harder to get rid of. Accurately diagnose the disease to see whether there are treatments you can use. Diseases like necrotic ring spots are untreatable.

4. Can Grass Diseases Spread To Other Parts of My Lawn?

Untreated grass diseases can spread, particularly in humid and hot environments. Acting quickly to manage the diseased area can help you prevent the spread.

5. What Preventive Steps Can I Implement To Prevent Grass Diseases?

Regularly mowing, correcting watering methods, using fertilizer, and ensuring good soil drainage can help you prevent the spread of grass disease.

6. Is It Advisable To Use Fungicides for Treating Grass Diseases?

Depending on the disease’s severity, using fungicides may be necessary to curb the spread of pathogens. Selecting the right fungicide and carefully following the instructions is essential.

7. Can I Replace Parts of My Lawn That Are Infected To Prevent the Disease From Spreading?

Yes, replacing the infected areas with healthy grass through reseeding or laying sod can stop the disease from spreading any further and prevent long-term damage.

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