Large Patch Fungus

As the weather cools, watch for Large Patch Fungus, especially on St. Augustine and Zoysia type grasses. This disease may affect any warm-season turf-grasses in Florida.  The disease development can be encouraged by a thick thatch layer, increased soil moisture, and low mowing heights. Excessive irrigation and late fertilization also improve the success of large patch in the lawn.

Large Patch Quick Facts: 

Pathogen: Rhizoctonia solani

Occurrence: This disease is most likely to be observed from November through May when temperatures are below 80F. It is normally not observed in the summer. Infection is triggered by rainfall, excessive irrigation, or extended periods of high humidity resulting in the leaves being continuously wet for 48 hours or more.

Symptoms/Signs: The fungus infects the leaf area closest to the soil, eventually killing the leaf. A soft, dark rot occurs at the base of the leaf, and leaves can easily be pulled off the stem. The base of a pulled leaf has a rotted odor. Roots are not affected by this pathogen. This disease usually begins as small patches about 1 foot in diameter that turn yellow and then reddish brown, brown, or straw colored as the leaves start to die. Patches can expand to several feet in diameter. It is not uncommon to see rings of yellow or brown turf in the center. Turf at the outer margin of a patch may appear dark and wilted.