Lots of lawns are suffering from the hot humid weather of last week. Temperatures were close to 30 C. These sorts of conditions put the lawns to a great deal of stress. This patch of lawn was newly sodded either this spring or last fall.
Large areas have turned brown. According to the homeowner, this happened very quickly.
Pythium is a disease that can be highly contagious and spreads quickly. Often, the lawn mower can be a cause of the disease spreading. In this situation, you can see the marks left in the lawn by the mower wheels. Where the disease was spread by the blades and mower body, the pattern is less distinct.
In some cases the lawn deteriorates quickly. Most often, the lawn will recover, but it may take some time. Overseeding will help to fill in some of the damaged areas.
To prevent further spread, refrain from watering that will leave the lawn damp through the night hours. Do not mow when the lawn is wet or in hot temperatures. Mow at 3" height minimum. Use a slow release fertilizer. We'd recommend something with 75% slow release nitrogen. Finally, mow the diseased areas last to minimize spread to the healthy parts.