Diseases are usually related to heat and moisture. The most susceptible months of the year are June, July, and August. High humidity along with the heat creates an ideal disease environment. However, poor irrigation practices can also promote disease development.
The longer moisture stays in the turf foliage, the greater the disease risk, which is why you should not water at night (between 10:00 p.m. and 4:00 a.m.) since the lawn will stay wet until morning. It is best to irrigate between 6:00 am and 8:00 am. Weather permitting, do not water established sod every day unless there is dry weather, or if the sod feels crunchy or looks dry.
When brown spots first appear, observe them for a few days. If more develop and you have ruled out the possibility of burns or improper watering, you probably have an active fungus. During periods of high humidity, small six-inch diameter spots may multiply, overlapping to become a large area. The grass may be collapsed to a point of lying matted, flat, and rotting. This is symptomatic of the fungus pythium. Reduce the frequency of watering so that the diseased areas will dry out.
Also, make sure that when water is reapplied it is between 6:00 a.m. and 8:00 a.m. Lightly rake up collapsed matted areas to help them air out and to prevent recovering shoots from suffocating. Use a broad-spectrum fungicide such as Daconil or Fore as recommended by your nurseryman. Always apply the fungicides according to label directions. You can also call a lawn care service to solve the problem.
Spraying will usually stop the disease from spreading. Be patient with areas that have been damaged; often a high percentage of recovery will occur over time. If re-seeding or sodding is required, wait until the cooler times of the year.