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Pythium Blight Control: Get Rid of Pythium Blight

July 10, 2023
Pride In Turf

Pride in Turf understands how important a well-manicured lawn is to many homeowners. That is our goal with our lawn fungus services, and we want the same for you. It is important to control Pythium blight, as it can quickly turn your green, lush lawn into a brown, diseased mess. We will delve into the details of this fungal disease - its symptoms and best practices to eradicate this destructive fungus from your lawn. We hope this information is useful in helping you keep a healthy lawn.

Understanding Pythium Blight

Pympythium blight is caused by the fungal pathogen Pythium spp., and is also known as cottony blight or grease spot. It is a common lawn disease that thrives in hot and humid climates, typically appearing during periods of high humidity with daytime temperatures above 86 degrees and night temperatures above 68 degrees. Excessive moisture, poor drainage, overwatering, and compacted soil are contributing factors that create an environment that is conducive for pythium blight development. If left untreated, it can spread rapidly, causing extensive damage to your turf.

The lawn fungus Pythium blight occurs mostly in cool season grass types, such as tall fescue, creeping bent grass or perennial rye grass; however, it can also impact warm-season grass types like Bermudagrass or Zoysia. The pathogens, Pythium SPP., thrive in warm and wet conditions, making them particularly prevalent during periods of highly humid or hot humid weather with excessive moisture. These pathogens can persist in the soil and thatch layer, waiting for favorable conditions to attack the turfgrass. Once the disease establishes, the lawn fungus spreads rapidly, leading to extensive damage.

Early fall through late spring are times when pythium blight is more common in the south. Pythium blight appears suddenly during hot, humid weather and is common in the wettest areas and in the surface drainage pattern. This lawn disease is harshest on immature grasses and seedlings and is not as commonly found in home lawns. This turfgrass, however, can plague commercial or residential landscapes.

Many pythium species cause diseases of roots, crowns, and/or foliage that result in a general decline of turfgrass stands. When the roots and crowns are attacked, the disease is called Pythium root rot. Disease may occur in small patches or involve large areas, especially on highly maintained golf course greens.

Even though there are many pythium species, pythium aphanidermatum is the primary species associated with pythium diseases in the US. The lawn disease often grows in lines following paths where water drainage occurs, or in a lawn's mowing pattern. Mycelium, the gray mold created by pythium aphanidermatum can survive in soil as well as on dead or cut grass blades.

Symptoms of Pythium Blight

Identifying Pythium blight early is crucial for effective pythium blight control. Pythium blight appears initially as circular, small patches, usually measuring one to three feet in diameter. The patches exhibit a dark brown or black water-soaked appearance, which may resemble a grease spot or irregularly shaped blotches. In the morning, a white, cottony growth (mycelium) may be visible on the patches.

The mycelium it most abundant when infected areas are wet. Once the infected grass dries, the disease becomes less visible and yellow patches appear where the greasy shapes were. Pythium aphanidermatum forms the gray mycelium or fruiting bodies

The mycelium produced by Pythium spp. is similar in appearance to other turfgrass diseases such as dollar spot and brown patch. As the disease progresses, the patches enlarge rapidly, often merging to form larger areas of dead, brown grass.

Pythium blight first appears as small, sunken circular patches up to one foot in diameter during hot, humid weather. In warm-season turf such as bermudagrass putting greens, pythium blight first appears as small black or purple spots. These can expand into larger irregular areas, especially during prolonged periods of huid rainy, and/or cloudy weather any time of the year.

Symptoms of pythium root rot may spread in drainage patterns during periods of heavy rainfall. The pathogen may cause seedling damping-off, or root rots. On individual plants, the crowns, roots rhizomes, and/or stolons will appear dark and greasy. The depth and density of roots will be drastically reduced in affected areas. Pythium root rot occurs in areas with high soil moisture, poor drainage, and low light. Disease can be severe in locations with low mowing height and excessive wear.

Control of Pythium Blight

Proper lawn management practices play a vital role in preventing and controlling disease development. There are many factors to consider in controlling pythtium blight in lawns, whether you have perennial ryegrass, tall fescue, kentucky bluegrass, annual bluegrass, or another type of turfgrass. Pythium blight is susceptible on all types of grass.

The following are some factors to follow in controlling pythium blight in your lawn:

Mowing Practices:

It is important to mow your lawn at the appropriate height and maintain the lawn at the appropriate height for your grass type and grass blades. This encourages healthy growth and air circulation. Also, keep your mowing equipment in good condition. It helps to mow frequently to maintain the appropriate height to help prevent pythium blight.

Avoid mowing wet, infected grass where mycelium is present to avoid spreading spores with the mower blades.


Avoid excessive watering, as too much moisture creates an ideal environment for disease development of pythium blight. The best method is to water your lawn deeply, but infrequently. The best time to water is in the early morning. This helps give the grass time to dry out during the day and avoid prolonged leaf wetness.

Ensure Proper Drainage:

You need to correct any drainage issues in your lawn to prevent standing water in your lawn as well the possible formation of stagnant water. Excessive soil moisture is a cause for pythium blight, so it is important to assure you have proper drainage to prevent lawn fungus. Ensuring proper drainage also helps during damp weather conditions.

Aerating your lawn regularly is important, as aeration helps improve soil structure and drainage. This reduces soil compaction and enhances water and nutrient uptake. This also helps reduce the risk of pythium blight.

Reduce Humidity and Increase Sunlight Exposure:t

If you have shady areas in your lawn or you have overhanging branches or structures causing areas of shade, this can create areas of excessive moisture, conducive to pythium blight. You cannot control cloudy weather or humid weather, but you can remove obstructions, where possible, to allow more air circulation and ability for damp areas to dry. It is important to improve drainage wherever possible to prevent pythium fungus and help your grass to grow green and lush.

Thatch removal is an important method if controlling pythium blight fungus.. You should dethatch your lawn regularly to prevent thatch buildup. Thatch buildup creates a humid environment promoting pythium blight.

Reseeding and Renovation:

You should remove and replace severely infected areas. If pythium blight has caused extensive damage to your lawn, remove the dead grass and reseed or resod the affected areas. Try to choose disease-resistant grass varieties. Fungicide treated seed is also available.

Chemical Control of Pythium Blight

In severe cases or when preventive measures are insufficient, chemical control may be necessary. However, it should be used as a last resort in conjunction with cultural practices. It is best to consult with a professional for appropriate fungicide recommendations, as formulations and application methods vary. Also, professionals, like Pride in Turf, have access to be best fungicides that are not available to everyone to treat pythium blight.

If you choose your own fungicide, find one labeled for pythium blight and appropriatefor your turfgrass species. Fungicides containing ative ingredients like mefenoxam etridiazole, or azoxystrobin are effective against Pythium spp.

Timing and application is important, so apply fungicides according to the label instructions, targeting the active growth period of Pythium spp. Make sure to cover the affected areas thoroughly and follow recommended rates and intervals.

To minimize the risk of developing fungicide resistance, alternate between different fungicide classes with each application. Avoid relying on a single fungicide for an extended period.


Controlling pythium blight requires a proactive and integrated approach. By understanding the disease, implementing cultural practices, enhancing soil health, and judiciously employing chemical control methods, you can effectively manage and prevent pythium blight in your lawn. Regular monitoring and maintenance are crucial for long-term success. Prioritize healthy turf practices to keep your lawn vibrant and disease-free.

For the best results to deal with pythium blight in your lawn, contact Pride in Turf. They are professionals and know exactly what your lawn needs and and know how to treat your turfgrass. The experts at Pride in Turf will work with you and develop a plan that works for you to help you get rid of pythium lawn fungus or any other lawn issues you may be having.

Pride in Turf wants your yard to be the envy of the neighborhood!

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