I just noticed what appears to be a fungus on the lawn. It is very localized to an area of less than 100 sf. It does not cover the whole area but runs in a couple of "stripes" about 12" wide. The pictures show it on the grass and I also found what appears to be the same thing around the base of a choke-cherry tree. The tree appears to be healthy but there are some spots (white) on it and I see some stress fractures in the bark. The area of lawn which is affected has 1) never manifest this before, 2) is similar in soil type, grass type and exposure to sun etc as a large area around it and 3) otherwise appears healthy (not much thatch, green). I haven't used any fertilizers or herbicides and usually keep it cut at 3". I'm wondering what it is, why its here, and what to do about it. Could it have come from the tree? My only other thought is that there is a pile of weed from the flowerbed just up the hill which have been sitting there for 6 weeks and are decomposing. Could something have leached out of the pile? Any suggestions are welcome and thanks in advance.