Thanks for the advice, but I've ruled out lack of water as a problem. I do
water regularly and we've had a very wet spring here. Th lawn didn't get a
chance to dry out. Now fungus is a possibility. How can you tell? Can fungus
cause the expensive problems that I have?- Hide quoted text -

Yes it can but I thought fungi were hard to identify--I lack the
experience. I had to have someone help me do it. On my lawn we
identified some slime mold that was leaving a black, powdery substance
in the grass blades http://en.wikipedia.org/wiki/Image:Slime_Mold_DP2.jpg
and read that this is harmless and does not hurt the lawn.