Hi, Well brown patches in the lawn can be caused by a number of factors: grubs, dog urine, disease, etc. I don't have a lot of information to on here, but I would start by raking the brown patches thoroughly and perhaps topping them with a little fresh soil. Then, sowing new grass seed over them. I would also spread a weed/feed product (some of these products also have a grub killer in them) on the lawn to help build it up and encourage thicker growth. A well fed lawn will generally fill in quickly, unless there are other problems like competing tree roots or dogs. You should not have to use a pesticide if you spread a grub killer with your weed and feed.