Brown spots in the lawn can be caused by a number of things but the most common is a lack of water. Check the irrigation coverage in areas that are thin or bare. Also, weedy areas may be the result of not enough water to maintain a healthy lawn.
Round, brown spots often with a greener, “frog-eye” center and a yellowish outside ring often indicate necrotic ring spot (NRS) disease. NRS is caused by a soil-born fungus. To manage the disease, do not over water and overseed with a resistant variety. Apply nitrogen in the fall. Spring applications may stimulate rapid growth and further the development of NRS disease.
Dog urine may be the cause of spots in the lawn. The high nitrogen content in the urine will often burn the lawn. The spot can be diluted with lots of water but an easier solution would be to train the dog to use a specific area of the yard.
Mites can cause brown spots in the lawn. Damage is caused primarily due to dry conditions. Water well in warm, dry areas. Water dry areas in the fall and during the winter when possible.
For more information, see the following Planttalk Colorado™ video(s).
For more information, see the following Colorado State University Extension fact sheets.