Can anyone help describe how to tell the difference between a lawn that is under "heat stress" and one in which actually has a disease? I've got numerous customers who have irrigation systems and I'm fairly certain they water regularly, but they still have brown areas (these are all Tall Fescue lawns, clay soil, in Raleigh, NC). I don't think these areas are diseased (brown patch) because we've been way too dry. Most of the grass blades are really thin and completely brown. Mowing seems to be fine (sharp blades, correct mowing height, etc.) Other areas of the lawn are fine, only certain areas affected. My Ag agent says the only way to tell is to send a sample to local university, but it seems most other turf pros don't have to do this. I'm losing customers because I can't tell the difference, HELP!