Her is an interesting situation that I have not seen before. The pictures come from Mike Vander Pol, superintendent at Emerald Hills golf course in Northwest Iowa. This is on a Kentucky bluegrass fairway with a history of Summer Patch caused by the fungi Magnaporthe poae. The symptoms clearly look like Summer Patch, however, I would not expect the hyphae forming a myclial mass around the outside of the ring. It was Pythium weather at the time that the pictures were taken, but Pythium is rare on Kentucky bluegrass and the mycelia mass is clearly around the circumference of the patches.
I had Mike treat a test area with Teramec SP (chloroneb), a pythium control and send a grass sample to the Iowa State Plant Disease and Insect clinic for identification. Mike reported to me that the Teremec did stop the hypha. The laboratory was able to find oospores of pythium on the sample and runner hypae in the roots. They were not able to clearly identify the species of the runner hyphae.
Evidently, the summer patch developed as is common on Kentucky bluegrass at this time of year. This weakens the grass in the infected area. That must have coincided with just the right conditions for Pythium development and the two diseases happened simultaneously. Like I said earlier, I have not seen that before.