Question
I have numerous spots (up to 12 " diameter) around 3 seperate trees where the lawn appears to have been stressed and subsequently died. I have underground sprinkers and use them on a regular basis. I also fertilize with a Scott 4 Plan schedule. I thought that maybe it was rabbits but the there are to many seperate spots. They are just around the base of the tree and it is almost as if something had dripped from the trees. Any suggestions?

Answer
James:

There are trees which do give off a substance which acts like an herbicide.  Without knowing the genus and species of tree, I can not speculate on this.

If the rest of the lawn is healthy, greens and growing well, it may just be that these areas are higher than surrounding soil and and, thus, dryer.  I have seen this also.

Other than these suggestions, I know of no other causes.  The circles sound like ideal distances away from the trees for easy mowing, however.  Trimming time is reduced.

Are there any fungal signs, like mushrooms, white mass below the soil?

Best wishes.