Every spring and fall, Charleston homeowners find the same thing. Circles of thin, tan grass show up in a lawn that looked fine a few weeks ago. The patches grow, sometimes several feet across, and the edges look orange or bronze. In most cases this is large patch fungus, the most common disease of warm season lawns in Charleston and across the Lowcountry. Many people still call it brown patch. Here is how to recognize it, why our lawns are so prone to it, and what actually works to keep it under control, based on Clemson Extension guidance.
Large patch vs brown patch: what is the difference?
Both diseases are caused by the same fungus family, Rhizoctonia. Brown patch is the name used for the disease on cool season grasses like tall fescue, and it shows up in hot, humid summer weather. Large patch is the version that attacks warm season grasses such as St. Augustine, zoysia and centipede. It prefers cooler weather.
Because most Lowcountry lawns are warm season grasses, what you are seeing in your yard in April or November is almost always large patch. The name brown patch has stuck around out of habit.
When large patch fungus shows up in Charleston
Clemson Extension notes that large patch is most active in late fall and again in spring. The fungus starts working as soil cools in the fall, often after the lawn has gone mostly dormant. Damage may not be obvious until spring green up, when the patches fail to turn green with the rest of the lawn.
Our mild, damp winters and wet springs make the Charleston area especially prone to it. Long periods of wet leaves, cool nights and heavy dew give the fungus exactly what it wants.
Grasses most affected
- St. Augustine: very common and often severe
- Zoysia: very common, and slow to recover because zoysia spreads slowly
- Centipede: common, especially where it is overfed or poorly drained
- Bermuda: can get it, but usually recovers faster because it grows so aggressively
How to identify large patch
Look for these signs:
- Circular or irregular patches of thin, tan or straw colored grass, from a foot to many feet across
- An orange, yellow or bronze border on the outer edge of an active patch, sometimes called a smoke ring
- Rotted leaf sheaths. This is the key diagnostic. Tug on a few leaves at the edge of a patch. If they pull away easily and the base of the leaf is dark and rotted, that is large patch.
- Doughnut shapes as the center of an older patch starts to recover while the edge keeps spreading
- Patches that return in the same areas year after year, often in low spots, near downspouts or where irrigation overlaps
Large patch is often confused with chinch bug damage, drought stress and dog spots. Chinch bugs cause damage in hot, dry, sunny areas in summer, not cool wet weather. Our article on chinch bugs in St. Augustine explains how to tell the difference.
What causes large patch in Lowcountry lawns
The fungus lives in most soils. It becomes a problem when conditions tip in its favor. Clemson lists these major contributors:
| Condition | Why it matters |
|---|---|
| Nitrogen in fall or early spring | Soft new growth at the wrong time feeds the disease |
| Leaf wetness over 10 hours | Evening watering and heavy dew keep blades wet all night |
| Poor drainage | Low spots and compacted soil stay wet |
| Excess thatch | Holds moisture near the crown of the plant |
| Wrong mowing height | Scalped or overgrown turf is weaker |
How to prevent large patch
Cultural practices do more than any product. Fungicides help, but they will not fix a lawn that stays wet and gets fed at the wrong time.
Time your fertilizer carefully
Avoid nitrogen in mid to late fall and in early spring. Wait until the lawn has fully greened up and soil has warmed in late spring. For St. Augustine, Clemson's calendar calls for nitrogen only in the late spring and summer months. Our guide on the best time to fertilize in Charleston lays out the schedule by grass type.
Water in the early morning only
Water between about 4 and 8 in the morning, and only when the lawn needs it. Evening watering keeps grass wet all night, which is the perfect setup for large patch. In the fall and winter, cut irrigation back sharply. Dormant lawns need very little water.
Fix drainage and compaction
Low spots that hold water after rain are large patch magnets. Core aeration relieves compaction and helps water move into the soil. Regrading may be needed for areas that stay soggy. See our article on when to aerate a lawn in Charleston.
Manage thatch and mow at the right height
Keep thatch under control, especially in zoysia and St. Augustine. Mow at the recommended height for your grass and keep the blade sharp. Bag or remove clippings from infected areas so you do not spread the fungus across the lawn.
Treating large patch with fungicides
Fungicides work best as a preventive, not a cure. Once the leaves are brown, a fungicide can stop the spread, but the damaged grass will not turn green again until it regrows in warm weather.
Clemson's guidance for lawns with a history of large patch is to apply a labeled fungicide preventively in early fall, around early October, when soil temperatures start dropping. A second application a few weeks later helps before the lawn goes dormant. A spring application may be needed if the disease becomes active again as the lawn greens up.
Use a product labeled for large patch on your grass type, and follow the label exactly for rate, interval and watering in. Rotating between fungicide groups helps prevent resistance. Right Stuff Lawn Care adds preventive large patch treatments to fertilization programs for lawns that have a history of the disease.
Frequently asked questions
Will large patch go away on its own?
Active patches often slow down when summer heat arrives, and the grass slowly fills back in. But the fungus stays in the soil and usually returns the next spring or fall if the conditions that caused it do not change. Fixing watering, drainage and fertilizer timing is what keeps it away.
Is large patch the same as brown patch?
They are caused by the same fungus group, Rhizoctonia. Brown patch refers to the disease on cool season grasses in hot summer weather. Large patch refers to the disease on warm season grasses like St. Augustine and zoysia in cool weather, which is what Charleston lawns get.
When should I apply fungicide for large patch in Charleston?
Clemson recommends a preventive application in early fall, around early October, for lawns with a history of large patch. A follow up application before dormancy and one in spring may be needed. Always follow the product label.
Can I reseed or resod large patch spots?
It is usually better to fix the cause first and let the lawn fill in once it is actively growing in late spring. If you resod a spot without changing drainage, watering or fertilizer timing, the new grass is likely to get infected too.