We planted about a 3" Red Oak this Spring and about a month ago the leaves started turning brown. I thought it was from the summer heat so I watered it quite a bit, but with no noticeable improvement. The other Red Oak across the yard has had no issues. Other trees and plants in the yard appear to be fine. I have treated the trees twice with Bayer Tree & Shrub Control previously. I am thinking of testing the soil next. I truly hope its not some problem like Sudden Oak Death or Red Oak Borer. Any thoughts?
Don't use any additional pesticides until you find out what is going on. Take leaf samples to local Extension office, see what help you can get there.