The Most Common Lawn Diseases in the Southeastern U.S.
Maintaining a lush, green lawn in the Southeastern United States can be challenging due to the region's warm, humid climate. This environment is ideal for various lawn diseases that can quickly turn a beautiful yard into an unsightly mess. Understanding these diseases and how to manage them is crucial for any homeowner looking to keep their lawn healthy and vibrant.
The most common types of lawn diseases in the Southeast include:
- Brown Patch Fungus
- Dollar Spot Fungus
- Large Patch Fungus
- Pythium Blight
- Leaf Spot/Melting Out
- Lawn Rust
- Gray Leaf Spot
- Take-All Root Rot
- Fairy Rings
- Summer Patch
Brown Patch Fungus (Rhizoctonia solani)
Brown patch fungus is one of the most prevalent lawn diseases in the Southeast. It primarily affects cool-season grasses like tall fescue and ryegrass but can also impact warm-season grasses such as St. Augustine and zoysia.
What Does Brown Patch Fungus Look Like?
- Circular patches of brown or tan grass that can range from a few inches to several feet in diameter.
- The outer edge of the patch may appear darker or smoke-ring-like, especially in the morning dew.
- Grass blades may have lesions that are dark brown with a light brown or yellow halo.
What Causes Brown Patch Fungus?
Brown patch fungus thrives in warm, humid conditions, with ideal temperatures ranging between 65°F and 85°F. The disease is exacerbated by excessive nitrogen fertilization, which can promote lush, dense grass that is more susceptible to infection. Poor drainage and overwatering create the perfect environment for the fungus to flourish, as the excess moisture prolongs leaf wetness and encourages fungal growth.
How To Treat Brown Patch Fungus
- Avoid overwatering and water early in the day to allow grass to dry out.
- Improve air circulation by mowing at the appropriate height and avoiding excessive thatch buildup.
- Use a balanced fertilizer and avoid applying excessive nitrogen.
- Apply fungicides containing azoxystrobin, propiconazole, or chlorothalonil if necessary, particularly in areas with a history of brown patch.
Dollar Spot Fungus (Sclerotinia homoeocarpa)
Dollar spot fungus affects both cool- and warm-season grasses, including bentgrass, bluegrass, fescue, and zoysia.
What Does Dollar Spot Fungus Look Like?
- Small, circular, straw-colored spots about the size of a silver dollar (hence the name).
- Spots may merge to form larger, irregularly shaped patches.
- Grass blades may exhibit hourglass-shaped lesions with tan centers and reddish-brown borders.
What Causes Dollar Spot Fungus?
Dollar spot fungus is primarily influenced by low nitrogen levels in the soil, which weaken the grass and make it more vulnerable to infection. Excessive moisture, particularly from dew or frequent, light watering, provides an ideal breeding ground for the fungus. The disease also thrives in temperatures between 60°F and 80°F, making it a common issue in spring and fall.
How To Treat Dollar Spot Fungus
- Maintain proper fertilization to ensure adequate nitrogen levels.
- Water deeply but infrequently, and avoid watering in the late afternoon or evening.
- Improve air circulation and reduce thatch.
- Use fungicides containing azoxystrobin, propiconazole, or iprodione if cultural practices are insufficient.
Large Patch Fungus (Rhizoctonia solani AG 2-2LP)
Large patch fungus primarily affects warm-season grasses such as zoysia, centipede, and St. Augustine.
What Does Large Patch Fungus Look Like?
- Large, circular patches of discolored grass that can grow up to several feet in diameter.
- Affected grass may appear orange or yellow at the edges.
- Patches may be sunken and have a thin, unhealthy appearance.
What Causes Large Patch Fungus?
Large patch fungus is favored by high humidity and temperatures between 50°F and 85°F. The disease is often aggravated by excessive thatch and poor soil drainage, which trap moisture and promote fungal growth. Overwatering and high nitrogen levels, particularly in the fall or spring, can also contribute to the development of large patch fungus.
How To Treat Large Patch Fungus
- Water appropriately and improve soil drainage.
- Reduce thatch through aeration and proper mowing practices.
- Apply balanced fertilizers and avoid high nitrogen levels in susceptible periods.
- Fungicides containing azoxystrobin, tebuconazole, or flutolanil can be effective, especially when applied preventatively in the fall or spring.
Pythium Blight (Pythium spp.)
Pythium blight, also known as cottony blight or grease spot, is a destructive disease that can rapidly devastate cool-season grasses like ryegrass and bentgrass.
What Does Pythium Blight Look Like?
- Greasy, water-soaked spots that quickly turn brown and die.
- Spots may coalesce into large, irregularly shaped patches.
- In humid conditions, white, cottony mycelium may be visible, especially in the early morning.
What Causes Pythium Blight?
Pythium blight thrives in conditions of excessive moisture and poor drainage, as the excess water creates a favorable environment for the fungus. High humidity and temperatures ranging from 70°F to 90°F further contribute to the disease's spread. Additionally, overfertilization with nitrogen can weaken grass and increase susceptibility to Pythium blight.
How To Treat Pythium Blight
- Improve drainage and avoid overwatering.
- Water early in the day to allow grass to dry.
- Avoid excessive nitrogen fertilization.
- Use fungicides containing propamocarb, azoxystrobin, or metalaxyl as a preventive measure during periods of high humidity and warm temperatures.
Leaf Spot/Melting Out (Bipolaris sorokiniana)
Leaf spot and melting out are often caused by the fungus Bipolaris sorokiniana. This disease commonly affects cool-season grasses such as Kentucky bluegrass and ryegrass.
What Does Leaf Spot/Melting Out Look Like?
- Small, dark brown to black spots on grass blades, which can eventually merge into larger lesions.
- The spots often have a yellow halo.
- Severe infections may cause the affected areas to die off, resulting in a general thinning of the turf.
What Causes Leaf Spot/Melting Out?
Leaf spot and melting out thrive in cool, wet conditions, particularly when temperatures are between 60°F and 75°F. The disease is exacerbated by high humidity and poor air circulation, which prolong leaf wetness and encourage fungal growth. Overwatering and excessive nitrogen fertilization can also contribute to the development of these diseases.
How To Treat Leaf Spot/Melting Out
- Avoid overwatering and water early in the day to ensure grass dries out by evening.
- Improve air circulation by mowing regularly and reducing thatch buildup.
- Use a balanced fertilizer and avoid excessive nitrogen application.
- Apply fungicides containing azoxystrobin, propiconazole, or chlorothalonil if necessary, particularly during periods of high humidity and frequent rainfall.
Lawn Rust (Puccinia spp.)
Lawn rust affects a variety of grasses, including bluegrass, fescue, and ryegrass. The disease is characterized by its bright orange, yellow, or red pustules.
What Does Lawn Rust Look Like?
- Small, pustule-like lesions on the undersides of grass blades, which may appear as orange, yellow, or red powdery spots.
- Affected grass may exhibit yellowing and stunted growth.
- Severe infections can lead to the loss of turf density and overall weakening of the grass.
What Causes Lawn Rust?
Lawn rust thrives in cool, moist environments with temperatures between 50°F and 75°F. The disease is favored by high humidity and low nitrogen levels in the soil. Poor air circulation and prolonged leaf wetness also contribute to rust development.
How To Treat Lawn Rust
- Ensure proper fertilization to maintain adequate nitrogen levels.
- Water deeply but infrequently, and avoid watering in the late afternoon or evening.
- Improve air circulation and reduce thatch through regular mowing and aeration.
- Apply fungicides containing triadimefon, tebuconazole, or myclobutanil if cultural practices are insufficient, especially during periods of high humidity.
Gray Leaf Spot (Pyricularia grisea)
Gray leaf spot is a disease that affects warm-season grasses, particularly St. Augustine and ryegrass.
What Does Gray Leaf Spot Look Like?
- Small, circular lesions on grass blades with a gray or tan center and a darker, reddish-brown border.
- Lesions may enlarge and coalesce, causing large patches of dead grass.
- Infected areas often have a grayish appearance, particularly under humid conditions.
What Causes Gray Leaf Spot?
Gray leaf spot thrives in warm, humid conditions, with ideal temperatures between 75°F and 85°F. Excessive moisture, high humidity, and poor air circulation can exacerbate the disease. Overfertilization with nitrogen and frequent mowing can also contribute to its development.
How To Treat Gray Leaf Spot
- Improve air circulation by mowing at the recommended height and reducing thatch.
- Avoid overwatering and water early in the day to allow grass to dry out.
- Use a balanced fertilizer and avoid excessive nitrogen application.
- Apply fungicides containing azoxystrobin, propiconazole, or flutolanil as a preventive measure during warm, humid conditions.
Take-All Root Rot (Gaeumannomyces graminis)
Take-all root rot is a serious disease that primarily affects warm-season grasses such as Bermuda and zoysia.
What Does Take-All Root Rot Look Like?
- Root systems are often rotted or decayed, resulting in poor grass growth and yellowing.
- Grass blades may show signs of wilting and thinning.
- Affected areas may develop circular patches of dead or thinning grass.
What Causes Take-All Root Rot?
Take-all root rot thrives in warm, humid conditions with temperatures between 70°F and 85°F. The disease is often aggravated by poor soil drainage, excessive moisture, and high soil pH. Overuse of nitrogen fertilizers can also contribute to its development.
How To Treat Take-All Root Rot
- Improve soil drainage and avoid overwatering to reduce moisture levels around the roots.
- Adjust soil pH to a more neutral range if it is too high.
- Use appropriate fertilizers and avoid excessive nitrogen application.
- Apply fungicides containing azoxystrobin, tebuconazole, or flutolanil as needed, especially in areas with a history of take-all root rot.
Fairy Ring (Marasmius oreades and other fungi)
Fairy rings are a common lawn issue caused by several species of fungi, including Marasmius oreades. These rings can affect various types of grasses, including both cool- and warm-season varieties.
What Do Fairy Rings Look Like?
- Circular patches of darker or greener grass with a ring of dead or brown grass around the outer edge.
- Rings can vary in size and may have a noticeable difference in growth rate within the affected area.
- In some cases, the rings may have a mushroom-like appearance in the center, especially during wet weather.
What Causes Fairy Rings?
Fairy rings develop when fungal mycelium grows in the soil, often due to organic matter or thatch accumulation. The fungi produce a growth pattern that results in a ring shape, with the outer edge of the ring having more vigorous growth due to the increased availability of nutrients. The disease is more common in poorly drained soils and areas with high organic content.
How To Treat Fairy Rings
- Improve soil drainage and reduce thatch buildup.
- Aerate the soil to improve root growth and reduce fungal activity.
- Avoid excessive watering and high nitrogen fertilization.
- Fungicides may be used in severe cases, with products containing propiconazole or chlorothalonil being most effective when combined with cultural practices aimed at reducing fungal growth.
Summer Patch (Magnaporthe poae)
Summer patch primarily affects warm-season grasses such as Kentucky bluegrass and perennial ryegrass. The disease is most commonly observed in lawns during the summer months.
What Does Summer Patch Look Like?
- Circular patches of turf that may range from a few inches to several feet in diameter.
- Affected grass may appear yellow or tan, often with a distinct sunken or depressed appearance.
- Patches may have a characteristic yellow halo around the edges, with the center of the ring often remaining green or healthy for a time.
What Causes Summer Patch?
Summer patch thrives in warm, humid conditions with temperatures between 65°F and 85°F. The disease is exacerbated by high soil moisture and poor soil drainage, which create a favorable environment for fungal growth. High nitrogen levels and thatch buildup can also contribute to the development of summer patch.
How To Treat Summer Patch
- Improve soil drainage and reduce excessive moisture by watering appropriately.
- Aerate the soil to reduce thatch and improve root growth.
- Use a balanced fertilizer and avoid high nitrogen levels, especially during the summer months.
- Apply fungicides containing azoxystrobin, propiconazole, or tebuconazole as a preventive measure, particularly during periods of high humidity and warmth.
Lawn Disease Treatments
Lawn diseases can be a significant challenge for homeowners in the Southeastern United States, but with proper identification and management, you can keep your lawn healthy and beautiful. Regular monitoring, proper watering, balanced fertilization, and good cultural practices are essential in preventing and controlling these common lawn diseases. If you suspect a severe outbreak or need assistance, consult our lawn care professional at Unlimited Lawn Care to provide the expertise and lawn disease treatments necessary to protect your lawn.