Pythium Disease in Warm-Season Lawns: Complete Guide

Pythium disease is one of the most rapidly destructive lawn problems in Florida, capable of killing large areas of turf within 24-48 hours under favorable conditions. The disease is caused by several Pythium species - water molds that thrive in saturated soil during hot weather. Florida's summer rainy season creates perfect conditions for devastating Pythium outbreaks.

The first symptoms appear as small, water-soaked patches that look dark and greasy, as if the grass has been scalded or soaked in oil. These patches can be circular or irregular and often appear first in low-lying areas where water collects. In the early morning, you may notice white, cottony mycelium covering the infected grass, similar to cobwebs. This mycelium collapses and disappears as the sun rises and the grass dries.

Pythium spreads remarkably fast - patches can expand from a few inches to several feet in a single day when conditions are right. The infected grass collapses and turns a slimy tan to reddish-brown color, and you may notice a distinctive "fishy" or sewage-like odor from severely affected areas. The grass blades often stick together in a matted, greasy mass.

Pythium commonly follows drainage patterns, moving downhill with water flow. You may see streaks of dead grass extending from higher areas to lower spots in the yard. The disease is particularly aggressive on over-watered lawns, compacted soils, and areas with poor drainage. Night temperatures above 68°F combined with daytime highs above 85°F and wet conditions create the ideal environment for explosive Pythium outbreaks.