Pythium spp. selectively attacking Poa

July 16, 2010 in Extension, Research

In an old post on the Turf Disease Blog, I briefly mentioned a strange Pythium problem that has shown up over the last few years. A few superintendents in the New York Met and select regions in the mid-Atlantic and Northeast may have heard me speak about this at a local conference, but for the most part this problem is not a widespread problem. I will make this disclaimer: we have very limited information on what is really going on with this Pythium and a majority of our info is from trial and error.

The disease, however, has likely been found on at least one course in the Pittsburgh region and is probably more widespread than we know.

Between 2005 and 2009, a dozen or so golf courses had issues controlling what was believed to be summer patch on their golf course putting greens. I had made trips to several of these courses to confirm that what we were seeing in the lab matched what was happening in the field. As it turned out, field symptoms were typical of the classic characteristics of summer patch. Further investigations in the lab revealed that a Pythium species appeared to be the culprit.

The Pythium was not a root disease, but was instead a foliar problem. While mycelium can be seen in small quantities following incubation, it does not “fluff” out like your typical Pythium blight. To see the mycelium, you need a hand lens or a dissecting microscope. Two separate Pythium species were routinely isolated from symptomatic samples. Isolates were identified via DNA sequencing and although the Pythium spp. are not new to turf, they are considered weak pathogens and generally not associated with severe Pythium infestations.

The weakly aggressive species may be the reason for the types of symptoms in the field. As mentioned, the symptoms of this disease are nearly identical to summer patch. The disease appears to selectively infect annual bluegrass and leaves the bentgrass to “fill into” the center of the declining patches. The patches may show up during late spring and the disease may remain active until late summer. Unlike typical Pythium diseases, the patch symptoms are SLOW to develop. Similarities among the courses that have dealt with this (from Maryland up to Massachusetts) include: 1) native soil putting greens with routine topdressing; 2) limited to no internal drainage, mixed bentgrass/annual bluegrass stands; and 3) reliance on Signature for the summer management of Pythium.

While the preventive applications of Signature have been shown to provide excellent suppression of Pythium blight as well as provide improved summer stress management, its influence on this particular problem remains unknown. In discussions with a colleague at the University of Florida, it appears that while Signature provides excellent suppression of the typical, more aggressive Pythium species, in vitro tests have shown reduced effectiveness on certain species (at least one of which are those isolated from our samples).

So what do you do about this potential problem?

1. Get samples diagnosed: This is not an easy one to diagnose and takes a little extra effort. Symptoms look identical to summer patch, which makes accurate identification even more difficult.

2. Utilize more traditional Pythium fungicides during summer: My recommendation has been to stay on your Signature program throughout the season to enhance your summer stress management. However, DO NOT RELY on these applications exclusively to suppress Pythium. My recommendations have been the preventive applications of something like Subdue or Segway when temperatures start to become conducive for Pythium.

3. Curative control with Banol: There have been limited to no trials for this disease on putting greens (if anyone is willing to have me create a quilt-patch of healthy and dead turf on their putting green, please let me know). What seems to work consistently for the curative control of this disease, however, is the foliar application of Banol. Do not water this in.

4. Improve Drainage: This is more of a long-term solution, but anything that can be done to improve the internal drainage on the putting green will help in managing not only this disease, but various other problems during the summer.

Remember, there is very limited research-based information on this problem. We will continue to monitor new cases closely, but unfortunately don’t have any real answers at this point (although the control measures mentioned above have been effective).