Not All Pythium Diseases are Created Equal

With the excruciating heat and humidity plaguing the Northeast, Southeast and Midwest, there has been numerous mentions of the notorious Pythium. Even the news media has caught wind of this nasty fungal-like organism (maybe that's why the columnist called it a bacterium). Check out Lane's post this week if you want to see what I am talking about.

So why are Pythium diseases problematic when the temperatures rise and relative humidity is through the roof? Pythium species are members of the Oomycota, which are commonly called water-molds. These organisms used to be classified as true fungi, but morphological and molecular evidence show that members of the Oomycota are more closely related to diatoms and brown algae. Yeah I know you don't care, but I do believe in the quote from The Art of War by Sun Tzu- "Know thy enemy and know thy self and you will win a hundred battles." It is vital to understand the pathogens you fight on a daily basis.

We have seen a number of different diseases induced by Pythium species, such as Pythium blight, Pythium root rot and even Pythium root dysfunction. However, the symptoms, signs and conditions favorable for disease development are different for these three diseases. Considering the recent weather conditions, I thought it would be good to review the differences between these diseases as well as the management strategies.

Pythium Blight- This disease has been the subject of nightmares for golf course superintendents for years. The fear most likely steams from the days when Pythium aphanidermatum developed resistance to metalaxyl and entire fairways were wiped out rapidly. Today we rarely hear of entire fairways devastated by Pythium blight, but the disease can develop even the Upper Midwest. However, the development is typically centralized around a drain or low lying area. If the disease is not controlled and hot, humid conditions persist the disease could spread at an alarming rate. Usually we only have 2 to 4 weeks of heat and humidity conducive for Pythium blight development in the Midwest, yet this summer has been a bit different than normal.

The symptoms of Pythium blight start as small, gray spots that can coalesce into larger areas of blight fairly quickly. Typically development of this disease will occur around drains or low lying areas of fairways. The picture just above the heading of Pythium blight is typical of the symptoms we see on creeping bentgrass in the Midwest. Cottony, white mycelium may also be present during early morning hours when dew is present. As for management, its a good idea to start thinking about Pythium blight when nighttime temperatures are above 70 to 75 degrees and when there is plenty of soil moisture. Fungicides that work best are Subdue MAXX, Stellar and Segway. Other products that may have varied results are Banol and Terrazole. Keep in mind that Signature works, but only when pressure is light to moderate.



Pythium root rot- Pythium root rot can be a major problem of golf course putting greens when there is persistent heat, humidity and low light intensity. This disease is also a problem on putting greens with limited air movement. One of the major problems with this particular disease is we know very little about the pathosystem. Consequently most the control recommendations are based on observations made by golf course superintendents. I think Lane posted about Pythium root rot sometime last summer and talked about the issues surrounding this disease.

The symptoms are usually diffuse, irregular areas that exhibit decline. The affected areas can decline quite rapidly because the pathogens destroy root tissue. The picture above is an example of typical stand symptoms. A noticeable decline in root depth is usually observed within affected patches. If you suspect Pythium root rot is an issue at your course, I suggest sending a sample to your local turfgrass pathologist for confirmation. Usually the best medicine for Pythium root rot is a Terrazole drench. Unfortunately, this disease can still develop even if you are on a good Pythium preventative program. Remember that most turfgrass fungicides only move up from the point of absorption, so in order to get Pythium root rot activity the fungicide needs to be washed into the rootzone.

Pythium root dysfunction- I know this is confusing, but Pythium root dysfunction is a totally different beast that Pythium root rot. The conditions that favor Pythium root dysfunction (PRD) symptom develop are hot, dry conditions not hot, humid conditions. PRD shows its ugly head on upland areas and develops into a discrete patch. Normally this disease is problematic for young putting greens built with high-sand content rootzones. I have blabbed on for a while on this post so check out a previous post by Lane for PRD management strategies.

To bring this belaboring post to an end, if you suspect any Pythium induced disease have it diagnosed by your local turfgrass pathologist. These diseases should not be taken lightly and all of them have different management strategies.