Left uncontrolled they can kill large sections of your lawn. This could be caused by a common disease problem called Red Thread. This disease causes pink, threadlike material on the surface of grass blades. Left uncontrolled, lawns will thin and eventually decline. Usually the lawn will recover with time.
Brown spots result from dog's urinating on the lawn.
Often the area surrounding the browned out grass will be a darker green. Water the affected areas to dilute the urine content in soil. Severely burned spots may require overseeding to fill in the spots in a lawn. Moles are very difficult to control. They forage through your lawn in search of insects and earthworms that they feed on.