Lawn Diseases: Identification, Prevention and Treatment

Lawn diseases manifest in different ways, from discolored patches to powdery coatings. Identifying symptoms early can prevent widespread damage and improve treatment outcomes. Here are some of the most common types of lawn disease and the most susceptible grass types they affect: 

Snow Mold (Early Spring Disease)

• Susceptible grasses: Kentucky bluegrass, perennial ryegrass, bentgrass, fescues
• Symptoms: Bleached, matted turf in irregular patterns
• Found in areas under heavy snowpack or in lawns left too long before winter

Snow mold is a common turfgrass disease that affects cool-season grasses. There are two types: gray snow mold and pink snow mold. Gray snow mold, caused by Typhula blight fungus, typically develops under prolonged snow cover. Pink snow mold, caused by Microdochium nivale fungus, can occur even without snow but thrives in cool, wet conditions. Affected areas may range from a few inches to several feet in diameter.

Solution: Lightly rake the affected areas in the spring and apply fertilizer to encourage new growth. Improving drainage and aeration can also prevent future outbreaks. For severe cases, dethatching may be necessary to remove infected material. Reducing the mowing height of a mower in the fall can also help reduce snow mold.

Red Thread (Spring Disease)

• Susceptible grasses: Perennial ryegrass, Kentucky bluegrass, fine fescues
• Symptoms: Red or pink fungal threads on leaf tips
• Most severe in cool, wet weather with persistent moisture

Red Thread, also known as Pink Patch, is a fungal disease commonly seen in the spring that affects cool-season grasses like tall fescue, Kentucky bluegrass and perennial ryegrass. It can also affect warm-season grasses like Bermudagrass. It is recognizable by the presence of red or pink threads extending from the grass blades. This disease thrives in cool, wet weather conditions with persistent moisture.

Solution: Light fertilization and collecting clippings help reduce fungal spread. Avoid overwatering, as excessive moisture encourages fungal growth. Keeping nitrogen levels balanced strengthens the grass and makes it less susceptible to infection. If the thatch layer of the turf is too thick or the soil is compacted, lawn aeration might be needed.

Dollar Spot (Early Summer Disease)

• Susceptible grasses: Bentgrass, Kentucky bluegrass, perennial ryegrass, fine fescues, Bermudagrass, centipedegrass, St. Augustinegrass, Zoysiagrass
• Symptoms: Small tan lesions shaped like an hourglass on leaf blades, possible morning fungal growth
• May be accompanied by spider web-like fungal growth in the morning

Dollar Spot is a turfgrass disease typically seen in late spring and early summer that creates small, silver-dollar-sized patches of dead grass, often merging into larger areas. It's caused by a fungal disease that thrives as temperatures and humidity begin to rise.

Solution: Light fertilization, infrequent but deep watering and clipping removal reduce disease severity. Increasing nitrogen levels can help turf recover faster. Proper mowing height and aeration improve airflow, making conditions less favorable for fungal development.  

While some lawn diseases are unavoidable, many can be prevented by following some lawn care tips. Here are some key strategies:

Proper watering: Water in the morning so the grass dries before nightfall, reducing disease-friendly moisture conditions. Deep, infrequent watering is preferable to shallow, frequent watering, as it encourages stronger root growth and reduces surface moisture. Avoid overwatering, as excessive soil moisture can lead to fungal diseases like Pythium blight.

Mowing correctly: Keep mower blades sharp and cut grass at the recommended height for your turf variety to reduce stress and susceptibility. Scalping the lawn weakens grass, making it more prone to disease. Additionally, alternate mowing patterns to prevent soil compaction and avoid creating conditions that favor fungal disease development.

Aeration: Reduces soil compaction and improves root health, making grass more resilient. Aerating enhances air circulation, helping to prevent fungal growth. Proper aeration can also help prevent the formation of patches of dead grass caused by turfgrass diseases.

Fertilization: Use the right amount of nutrients to prevent deficiencies and excess nitrogen, which can promote disease. Conduct a soil test to determine the appropriate fertilizer mix for your lawn’s needs if disease symptoms persist. Balanced fertilization supports healthy growth and can help prevent diseases caused by nutrient imbalances.

Dethatching: Remove excessive thatch buildup to improve airflow and reduce moisture retention. A thatch layer thicker than half an inch can create an environment where fungi thrive, especially under snow cover, leading to diseases like gray snow mold and pink snow mold. 

There is no universal treatment for lawn diseases because their development depends on multiple factors. Fungicides are often used as preventatives rather than cures, meaning they work best before a disease takes hold.

The best treatment approach involves improving cultural practices:

Watering adjustments: Reduce overwatering and avoid nighttime irrigation. Water early in the morning to allow excess moisture to evaporate throughout the day. This helps prevent fungal diseases that thrive in humid weather conditions.

Mowing adjustments: Keep grass at the proper height and remove infected clippings to minimize disease spread. Sharpen mower blades regularly to ensure clean cuts that heal quickly. Proper mowing can prevent the spread of fungal spores and reduce the severity of turfgrass diseases.

Aeration and overseeding: Aeration will improve drainage, build roots and create healthy grass plants that are more resistant to diseases. Overseeding with resistant grass types, such as certain types of tall fescue, can help your lawn recover from disease damage more quickly.

Applying fungicides selectively: If a severe outbreak occurs, fungicides may be necessary. Choose a product suited to the specific disease and follow label instructions carefully. Rotating fungicides with different active ingredients helps prevent resistance. For diseases like Pythium blight, timely fungicide application is crucial due to the rapid progression of the disease.

Since diagnosing lawn diseases can be tricky, professional lawn care services like TruGreen have the expertise to properly identify, diagnose and develop treatment plans for affected lawns. Consulting an expert can save time and ensure your lawn receives the best care.