I renovated my lawn 3 years ago after a terrible drought. Thanks to the great information offered by so many of you on this site my lawn has looked beautiful since the renovation. Until now. This past August and September we were still having heat well into the high 90's. I received an alert from Turf Files @ NC State stating that even though the temperatures were running above recommended temperatures for over seeding they still recommended Fall over seeding by mid-September. So I followed my normal routine starting with a soil test (everything was in balance), aerated, applied my annual lime, used a slit seeder to over seed and starter fertilizer. Watered 3x daily until the first cutting and put down the winter fertilize in early November. The lawn looked great - for about a month. We had one of the coldest winters on record so I expected the lawn to take a beating but for some reason I have lost about 25% of the lawn and now have huge bare spots. I planned on doing my usual split pre-emergent / fertilizer application (half now the balance in mid-April) but was told that I could forget about over seeding this Spring to repair the lawn if I use a pre-emergent now. Shemin's recommended I skip the pre-emergent and over seed now and in about 6 or 7 weeks put down Dimension with a fertilizer. One of my neighbors suggested I add Bluegrass to my normal Tall Fescue blend to help fill in the bare spots but I have a lot of trees hence several shady areas so I'm concerned the Bluegrass could be more problematic than helpful. Also, I swear by Shemin's Tall Fescue blend and they don't have one with any Bluegrass so would I try to mix the two in the slit seeder or apply the Bluegrass separately? Finally, I use an irrigation well for my lawn (had it installed 3 years ago after the drought and water restrictions) is it possible the well water is causing the damage? Sorry this post is so long but I thought I would try to answer any questions in advance. So thanks for your patience and as usual your advice is greatly appreciated.