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Tag: Pythium foliar blight

Hot + humid + rain = conditions for Pythium foliar blight

(Megan Kennelly, KSU Plant Pathology)

Here is a turf sample that came in this week. After one night in a moist chamber, there was an obvious cobwebby growth:

Notice how the turf looks matted down and greasy, too.

In the microscope here is what I saw – hyphae (fungal threads) with no crosswalls. This means Pythium foliar blight.

Pythium is not a true fungus, and many fungicides that work for other turf diseases do not work for Pythium blight. For a list of products that can handle Pythium, you can check out this resource (scroll to page 23-24):


In addition, don’t forget that foliar Pythium is different from root Pythium. With foliar Pythium, we see it most often in fairways, tees, and athletic fields. It is extremely rare in putting greens in Kansas. It is also rare in home lawns, but it can happen there from time to time.

Pythium loves water and lush turf. To reduce your risk, avoid over-watering and watering at night. Avoid excessive N. As a special bonus that will reduce the threat of brown patch too! Pythium can easily track with mowers and in with water-flow through drainage. Avoid mowing Pythium areas when it is wet, with mycelium, to avoid tracking it into other areas.

There are more tips here in Identification and Management of Turfgrass Diseases.

The cottony, cobwebby growth can be confused at times with brown patch. If you have any doubt, send some in to the lab.

Unlike Pythium, the brown patch fungus produces distinctive cross-walls in the hyphae:

And here is one more to show cross-walls vs none:


Here are some images of what Pythium foliar blight can look like in the field. You can see how it might be confused with other problems. When in doubt, send something in.


Tracking with a mower:


Not super distinctive…

…but upon closer inspection some mycelium was visible:

After a night in a moist chamber the mycelium was all over:

In the lab, that mycelium did not have cross walls.


Here’s one more shot of Pythium foliar blight in a low area on a bentgrass fairway:


Hot and sticky summer weather = brown patch and Pythium

(Megan Kennelly, KSU Plant Pathology)


Is this brown patch in a tall fescue home lawn? Look for lesions to be sure! See below!

It’s that time of year when you go outside in the morning and immediately start to sweat. Ugh.

High humidity means that the temperatures stays high even overnight. Sticky, humid nights = conditions ripe for brown patch and foliar Pythium.

Brown patch is common in tall fescue lawns, perennial ryegrass athletic fields and fairways, and bentgrass putting greens. I’ve been hearing reports of brown patch popping up in the past few days.

Foliar Pythium is common in bentgrass and rye fairways, and we occasionally see it in lawns that are very lush and wet. Foliar Pythium is very rare on greens. I haven’t seen any yet, but with humidity and nighttime lows in the 70s it’s a possibility.

Fungicides and cultural practices for both diseases are spelled out in detail in the publication Chemical Control of Turfgrass Diseases.


In tall fescue, brown patch symptoms can resemble drought or other injury. If in doubt, check around for the characteristic lesions:

Both diseases can produce mycelium in the turf during wet, humid, dewy mornings. With Pythium, usually the turf looks matted down and greasy.

Brown patch:

Pythium – grass is matted down and greasy/mushy:

Not sure? You can always send a sample to the KSU Plant Diagnostic Lab.

Pythium foliar blight in ryegrass and bentgrass tees and fairways

(Megan Kennelly, KSU Plant Pathology)

I haven’t received any Pythium foliar blight samples yet, but I wanted to provide a heads up and reminder.

Pythium foliar blight, sometimes called cottony blight, is one of the most destructive turfgrass diseases.  The disease can explode in only a few days if conditions are right. Perennial ryegrass and tee- or fairway-height creeping bentgrass are the most common hosts in Kansas. Though Pythium root rot (caused by different species) is common in putting greens, Pythium foliar blight is rare in putting greens. In 10 years, I have seen it only ONE time on a putting green. Tall fescue, Kentucky bluegrass, bermudagrass, and zoysiagrass can become infected, but this is extremely rare.

Conditions for Disease Development

The risk of Pythium blight is highest during humid weather when day temperatures are 86 to 95 degrees Fahrenheit and overnight lows are consistently at least 68 degrees Fahrenheit.

The disease is most common when soils are saturated with water, due to excessive rainfall or irrigation. Long dew periods, high relative humidity, and lush, dense turfgrass growth also favors disease development. Low areas, sites with poor air flow, and sites with poor drainage are particularly vulnerable.


In fairway-height bentgrass and perennial ryegrass, the first symptoms are irregularly shaped, water-soaked, greasy patches up to 4 inches in diameter.

Pythium in rye fairway

If it is humid, a cottony growth may be present early in the morning.

IMG_6412 IMG_6411

The patches may merge into larger blighted areas.

pythium 2006-2

The pathogen can be spread by equipment  and in water drainage patterns. Here is some Pythium blight at Rocky Ford a couple of years ago, following the pattern where heavy rain caused a water flow across this plot from left to right.

r ford pythium blight

Look-alikes: Pythium blight can be confused with brown patch, damage due to thick thatch, drought stress, or grubs. Brown patch is active during these same conditions. If you have any doubt, you can always send a sample to the diagnostic lab.


Pythium thrives in water, so water management is the key to Pythium blight control. The following practices will reduce the risk of other diseases (and stresses), too:

  • Improve drainage in areas where water is likely to stand for any length of time.
  • Avoid overwatering, especially during hot, humid periods.
  • Promote rapid turfgrass drying by proper spacing and pruning of shrubs and trees.
  • Fans can improve airflow in closed-in areas where collars and approaches have a history of disease.
  • Irrigate in the early morning to reduce the number of hours of leaf wetness.
  • Excessive nitrogen fertilization stimulates lush growth that is more susceptible to Pythium blight. Maintain a proper balance of nutrients and avoid fertilizing during periods of Pythium blight activity.
  • If active mycelium is present, avoid mowing, which can spread the pathogen.

Preventive fungicide applications during the summer months may be necessary on perennial ryegrass or creeping bentgrass golf fairways.

Below is the Pythium blight fungicide information from Chemical Control of Turfgrass Diseases by Paul Vincelli and Gregg Munshaw at University of Kentucky. You can click the image below to zoom. For the full guide, visit HERE.