Pythium Root Rot....Is it a disease or not?

Hot and wet weather during July and August typically brings outbreaks of Pythium root rot on creeping bentgrass and bermudagrass putting greens in the Southeastern United States. Symptoms of this disease usually appear as a yellow to orange, irregular dieback that is most severe in poorly drained or stressed areas. In some cases, however, Pythium root rot can develop in distinct spots and patches. These patches may be yellow, orange, or even purple in color.

Pythium root rot requires wet soils in order to develop, either from poor drainage, over-irrigation, or frequent rainfall. In fact, some pathologists argue that Pythium root rot isn't a real disease; they believe that the saturated soils are killing the turf and that the Pythium is simply colonizing dead roots. It's a 'chicken and the egg' type argument - no one knows for sure which came first.

I tend to believe that Pythium root rot is a real disease, simply because curative fungicide applications help to stop the problem and encourage turf recovery. That being said, if you have chronic problems with Pythium root rot, the only effective way to manage this disease long term is to improve soil drainage. All of the fungicides in the world will not provide adequate control if the soil is continuously saturated.

From the descriptions above, it is clear that Pythium root rot symptoms are highly variable and can be confused many other problems. Because of this, it is almost impossible to definitively diagnose this disease in the field. Curative fungicide programs for Pythium root rot are expensive, so a misdiagnosis can be costly. If you suspect that you have Pythium root rot, send a sample to a diagnostic lab for confirmation.

Few fungicides are labeled for Pythium root rot control, and there is virtually no scientific data regarding their effectiveness. For preventive applications, applications of mefanoxam, fosetyl-Al, or propamocarb every 14 to 21 days are recommended. An occasional application of ethazole is never a bad idea, especially during periods of wet weather.

For curative applications, I recommend an application of ethazole to provide quick knock-down of the disease, followed a few days later with a mefanoxam application. This is a program that I 'borrowed' from Bruce Martin at Clemson several years ago, and it works like a charm.

To minimize the potential for foliar burn, ethazole must be watered-in immediately after application with at least 1/8” of water. Applications of mefanoxam or propamocarb should also be watered-in, but fosetyl-Al should be applied to the foliage for best results.

For more information about Pythium root rot, please refer to TurfFiles.