Large Patch in Florida Lawns
Large patch, also known as rhizoctonia blight, is a fungal disease that affects lawns throughout the Southeast. It attacks all warm-season turfgrasses but is especially problematic in St. Augustinegrass and zoysiagrass.
Fungicides can stop the spread of large patch in the short term but to avoid yearly battles with the disease, we suggest adjusting your lawn care practices. Seasonally appropriate lawn management will improve the overall health of your lawn and make it less susceptible to large patch and other fungal diseases.
Cause and Symptoms
Large patch is caused by a fungal pathogen, Rhizoctonia solani. This disease is most often observed when temperatures drop below 80 degrees, usually between November and May. It often becomes a problem in fall, when cooler temperatures and damp weather create ideal conditions for the fungus. Damaged patches will continue to expand in the spring, until temperatures climb above those favorable for disease. In summer the damaged lawn may re-grow, filling in the dead patches. Unfortunately, if the disease isn't controlled, the problem will return again in fall.
Symptoms of large patch are readily observable. Turf damage begins with round, discolored patches that expand over time. The borders of the patches are darker where the fungus is actively growing and sometimes appear orange. The center of a patch is usually brown and sunken, but if the turf is recovering and actively growing, it may include signs of healthy growth.
To distinguish large patch from other lawn issues, pull a blade of grass from the outer edge of the affected area. If the leaf pulls easily off of its stem, and if the base is dark and smells of rot, a fungal disease is likely the culprit. Contact your county Extension office for help identifying the fungus.
Disease Management and Control
As with most fungal diseases, moisture is a primary contributing factor to large patch. Excessive irrigation, rainfall, and high humidity all contribute, but homeowners are only in control of their management practices. Incorrect watering, mowing, and fertilizing practices all make your grass more susceptible to disease.
The best way to treat large patch is also the best way to prevent it: make sure that your lawn care is seasonally appropriate. Minimize the time your lawn spends damp by watering only when necessary, and always in the morning. To avoid feeding the fungus, apply only slow-release nitrogen and do so sparingly, according to IFAS recommendations for your turf species and location. Finally, steer the lawn mower over the diseased areas last. Clean the mower blades afterwards to avoid contaminating new areas. Cultural practices like these can stop the spread and encourage regrowth in the affected areas.
If cultural practices fail to stop large patch, fungicides are also available. These chemical control methods are most efficient and effective when applied where disease has occurred in previous years; this is where it is most likely to occur again. Apply the appropriate fungicide about two weeks before symptoms usually show up. In most years, applications in North Florida should be made at the end of September. In South Florida, apply at the end of October.
Applications made after symptoms have appeared will stop the growth of the fungus but the product may need to be reapplied. Do this through the winter months or until turf begins actively growing to fill in the damaged patches. If the turfgrass is otherwise healthy, regrowth should happen naturally over the course of one or more growing seasons.
As always, we’d like to remind readers that the label is the law. The first step in using any pesticide safely is to read the product label to learn how the product may legally be used. For questions about specific pesticides, please contact the UF/IFAS Pesticide Information Office.
For assistance diagnosing or managing large patch, contact your county Extension office. The UF/IFAS experts are here to help you apply the most up to date research on this and other fungal diseases.