Large patch symptoms may occur anytime during the growing season, but they are most common in spring and fall as zoysia, centipede, and St. Augustine are either entering or breaking from winter dormancy.
Large patch disease is caused by a soilborne fungus called Rhizoctonia solani. This fungus is very similar to the one that causes brown patch disease of cool-season turfgrasses in mid-summer.
As its name implies, Large Patch Disease results in the formation of large patches of blighted turf that may exceed 20 feet in diameter. The disease occurs on both residential lawns and golf courses, but it is more severe when the grass is mowed to heights of less than one inch (i.e. golf course fairways) and where soil drainage is poor.
Symptoms of large patch appear in roughly circular patches from 2' up to 10' or more in diameter. The affected turf will initially be orange, yellow, or reddish-brown in color but will then turn tan and collapse to the ground. The disease can spread rapidly to encompass large areas of turf, and distinct circular patches may not be obvious in these cases.
Large patch of Zoysia is a disease that can wreak havoc on any lawn during relatively cool and wet conditions. The disease is most common in the early spring and late fall as the turf is entering winter dormancy or breaking dormancy.
Large Patch is commonly associated with turf in shaded areas or areas that tend to stay moist in the summer months. These patches can develop each spring and fall in the same locations unless proper control measures are taken. The disease forms irregular patches that can range in size from 2' to up to 20' in diameter.
The spring patch symptoms appear as light brown sunken areas that are slower to recover from dormancy than surrounding turf. As the soil temperatures rise throughout the summer, the disease is suppressed until the return of more favorable conditions in the fall.
Fall disease symptoms are bright orange patches of matted turf. The patch attacks the leaf sheaths near the thatch layer of the turf. The disease does not damage the roots or stolons during the infection process so rarely does this disease completely kill large areas of zoysia grass.
Controlling large patch can be accomplished with cultural practices as well as chemical applications. Excessive soil moisture should be avoided so as to not promote large patch. Poorly drained areas should be corrected and turf grass areas should not be over watered.
Thatch should also be kept in check. Thick thatch layers serve as over wintering sites for the disease. Verticutting and core aerification should be performed each year to limit thatch accumulation and eliminate disease habitats.
Fungicides containing the active ingredient triadimefon are very effective for large patch control and are available in garden centers and home improvement stores. Sprayable formulations of triadimefon are more effective than spreader-applied granular products. Products containing azoxystrobin (Heritage) or flutolanil (ProStar) are also very effective but are generally only available to professional landscape managers.
For those areas with a history of large patch, make a single preventive fungicide application in late September to early October. Don't delay the fungicide application! A preventive fungicide application not only inhibits fall infection, but also suppresses or delays disease development in the spring.