Pythium species management controls and recommendations
Managing Pythium species is challenging, especially in the transitional climate zone where temperature extremes complicate disease timing and fungicide efficacy. The following are the current recommendations for managing Pythium blight, Pythium root rot and Pythium root dysfunction. The symptoms, development factors and cultural and chemical control are summarized.
Pythium Blight
Pythium blight first appears as small, sunken, circular patches up to one foot in diameter in cool-season turf during hot, humid weather. In warm-season turf, such as bermudagrass putting greens, Pythium blight first appears as small black or purple spots that can expand into larger irregular areas, especially during prolonged periods of humid, rainy and/or cloudy weather any time of the year.
These symptoms can easily be mistaken for leaf spot, so be sure you obtain an accurate diagnosis. Leaves within affected areas are matted, orange or dark gray in color and greasy in appearance. Gray, cottony mycelium may be seen in the infected areas when the leaves are wet or humidity is high. The disease spreads rapidly along drainage patterns and can be tracked by equipment. This disease can cause widespread damage to a turf stand very quickly when conditions are favorable for development.
Development Factors
Pythium blight may develop when night temperatures exceed 65°F in cool-season turf (50°F for warm-season turf), and leaves are continually wet for 12 to 14 hours for several consecutive nights. For this reason, severe Pythium blight epidemics in cool-season turf are commonly observed the morning after a late afternoon or early evening thunderstorm in the summer. Daytime temperatures above 85°F also encourage Pythium blight development in cool-season turf, possibly due to increased stress. Excessive soil moisture and succulent foliar growth also favor disease development.
Perennial ryegrass and annual bluegrass are most prone to Pythium blight and can sustain significant damage in two to three days if conditions are favorable. Creeping bentgrass and tall fescue are more resistant to the disease but can be severely affected if conditions are conducive for prolonged periods. Bermudagrass putting greens are susceptible to Pythium blight during extended periods of humid, rainy and cloudy weather most any time of the year when temperatures are above 50°F.
Cultural Control
Reduce prolonged leaf wetness by watering before sunrise in the early morning hours. Avoid excessive nitrogen rates to prevent lush, succulent foliar growth, which is very susceptible to Pythium blight. Cool-season turfgrasses should not be fertilized with more than 0.25 lbs. N per 1,000 square feet when conditions favor Pythium blight activity. Avoid establishing turf in low-lying areas that will collect water. If necessary, install subsurface drainage to prevent wet soil conditions. Relieve compaction and maintain soil drainage through hollow tine aerification, and topdress golf course putting greens regularly to minimize thatch accumulations.
To minimize the pathogen’s spread, do not mow or irrigate when Pythium mycelium is on the foliage. Collect and promptly dispose of clippings from infected areas and ensure that mowing equipment is washed before entering an uninfected area.
Chemical Control
Due to the potential for rapid development of this disease, high-value areas and susceptible grasses should be protected with a preventive fungicide program. Applications should be initiated when night temperatures consistently exceed 65°F for cool-season turf (50°F for warm-season turf) and repeated on 14- to 21-day intervals as directed on the fungicide label when conditions favor Pythium blight development.
Pythium Root Rot
Pythium root rot is a persistent problem in poorly drained or over-irrigated areas. The disease can also occur in well-drained areas following extended periods of rainfall. Pythium root rot can occur at any time of the year if the soil remains saturated for several days or weeks. Symptoms are orange or yellow from a distance and usually appear in irregular patterns but occasionally develop in spots or distinct patches. Symptoms of Pythium root rot may spread in drainage patterns during heavy rainfall. The crowns, roots, rhizomes and/or stolons will appear dark and greasy on individual plants. The depth and density of roots will be drastically reduced in affected areas.
Development Factors
Many species of Pythium can cause root rot in turfgrasses. As a result, if the soil remains saturated for prolonged periods, root rot can develop at any time during the growing season. Poor surface or subsurface drainage, over-irrigation, heavy rainfalls and excessive thatch and organic matter accumulation are the most common factors that lead to a root rot outbreak.
Cultural Control
Avoid establishing turfgrasses in poorly drained areas that remain saturated for extended periods. Golf course putting greens must be aerified and topdressed regularly to control thatch and reduce organic matter accumulation. Generally, 15 to 20 percent of the putting green surface area should be impacted by hollow-tine aerification annually, and 5,000 pounds of topdressing should be applied per 1,000 square feet each year.
Pruning or removal of trees surrounding putting greens to increase sunlight penetration and air movement will reduce Pythium root rot activity. Installing high-powered fans will also help alleviate the problem of restricted air movement. Reconstruction is the only practical long-term solution for golf course putting greens with poor internal drainage for Pythium root rot.
Chemical Control
Where this disease has been a persistent problem, apply labeled fungicides every 14 to 21 days during the growing season or when rainfall occurs for two to three consecutive days. For curative applications, first apply etridiazole, followed by an application of cyazofamid, picarbutrazox, mefenoxam, or propamocarb two to three days later. To minimize the potential for foliar burn, etridiazole must be watered in immediately after application with at least 1⁄8 inch of water. Other fungicides should also be watered in with at least 1⁄8 inch to drive the active ingredient into the root zone where the Pythium root rot pathogens are most active.
Pythium Root Dysfunction
Pythium root dysfunction is a disease caused by creeping bentgrass putting greens, and it is most damaging to greens constructed within the last 10 years. The pathogen infects bentgrass roots during the fall and spring and reduces their ability to absorb water and nutrients from the soil. Symptoms may appear at any time of year but are most severe during hot, dry weather. Pythium root dysfunction appears in circles or irregular patches up to two feet in diameter that initially show signs of wilt or nutrient deficiency.
As the disease progresses, affected areas turn orange and decline, eventually collapsing to the ground. Infected roots are tan in color and lack root hairs, which causes the sand to fall easily from the roots when examining a soil probe sample. Reductions in root depth may not be evident during the fall and spring, but roots infested with Pythium species associated with PRD die back rapidly when soil temperatures exceed 85°F.
Development Factors
Pythium root dysfunction infects creeping bentgrass roots in the fall, winter and spring when mean daily soil temperatures are between 50°F and 75°F. Disease activity reduces the turf’s ability to absorb water and nutrition from the soil and also leads to rapid root dieback when soil temperatures exceed 85°F. Therefore, the appearance of Pythium root dysfunction symptoms is enhanced by low fertility, drought stress and low soil oxygen levels. Symptoms are most common during hot weather in summer but may also appear during warm, dry conditions in fall, winter or spring.
Cultural Control
To provide adequate water and nutrient-holding capacity, creeping bentgrass greens should be constructed with at least 10 to 15 percent organic matter by volume. After establishment, creeping bentgrass should be fertilized with 4 to 6 lbs. N per 1,000 square feet annually, depending on climatic conditions. Regular soil and tissue testing should ensure that all other nutrients are present adequately. Raise mowing heights to 0.125 inches during summer to increase photosynthesis and alleviate stress.
Avoid severe drought stress by irrigating before wilt symptoms become widespread and supplement with syringing and hand watering areas that dry out more quickly. Soil surfactants increase soil moisture uniformity across putting greens and assist with water management.
Plus, frequent cultivation and topdressing are needed to maximize oxygen levels in the soil. Generally, 15 percent to 20 percent of the putting green surface area should be impacted by hollow tine aerification annually, and 5,000 pounds of topdressing should be applied per 1,000 square feet yearly. Biweekly solid tine aeration during summer will increase root survival.
Chemical Control
Standard Pythium fungicides, such as mefenoxam (Subdue Maxx) and propamocarb (Banol) have provided poor to moderate control of Pythium root dysfunction when applied alone. The most effective fungicides in recent trials at NCSU have been picarbutrazox (Serata), cyazofamid (Segway) and fluopyram/prothioconazole/propamocarb (Resilia).
Fungicides may be used on either a curative or preventative basis for Pythium root dysfunction control. Both strategies employ the same fungicide rotation with all applications watered in immediately with 1/8 inch of post-application irrigation:
1. Serata (0.6 fl oz per 1,000 square feet)
2. Resilia (4 fl oz per 1,000 square feet)
3. Segway (0.45 fl oz per 1,000 square feet)
Serata should be applied for preventative control every 21 to 28 days in the fall and spring when mean daily soil temperatures are between 50°F and 75°F. Curative applications should be made every 14 to 28 days based on the appearance of symptoms.
In recent trials, we have not observed significant differences among QoI fungicides when used alone for Pythium root dysfunction. Regardless of which fungicide is applied, effective curative control also requires increased mowing heights and nitrogen inputs to relieve stress and allow the affected plants to heal.
Source: Jim Kerns and Lee Butler, NC State University Extension, Turfgrass Diseases. Pythium blight, Pythium root rot and Pythium root dysfunction. Last updated 2025.
Jim Kerns, Ph.D., is a professor and extension specialist of turfgrass pathology at North Carolina State University in the Department of Entomology and Plant Pathology. For more information, contact him at jpkerns@ncsu.edu.
Lee Butler, M.S., is an extension coordinator at North Carolina State University in the Department of Entomology and Plant Pathology. For more information, contact him at ebutler@ncsu.edu.
Related Articles
Subscribe to Golfdom
If you enjoyed this article, subscribe to Golfdom to receive more articles just like it.
