Lawn care tips
Brown Circles in Your Lawn This Fall? It's Probably Large Patch
If round brown patches are opening up in your lawn as the weather cools, and they are getting bigger rather than staying put, you are almost certainly looking at large patch. It is the most common cool-season lawn disease in North Florida, it particularly likes St. Augustine, and the window for getting ahead of it is narrow.
How to know that is what you have
Large patch is caused by a fungus, Rhizoctonia solani, and it leaves a fairly distinctive calling card.
Look for round patches that expand over time. That expansion is the tell. Drought stress, a fuel spill, a dog, or a buried piece of construction debris all make brown spots, but they make brown spots that stay roughly the same shape. A fungal patch creeps outward week to week.
Then look at the edge. UF/IFAS describes the borders as darker where the fungus is actively growing, and notes they “sometimes appear orange.” The center of a patch is “usually brown and sunken.” That orange-ish leading edge on an expanding circle is about as close to a diagnostic signature as lawn problems get.
| What you see | Large patch? |
|---|---|
| Round patch, expanding weekly, darker or orange edge | Very likely |
| Brown area, fixed size, sharp straight edges | No, look for a physical cause |
| General overall yellowing across the whole lawn | No, more likely nutrition or cold |
| Irregular patches that spread in hot weather | Different problem, possibly chinch bugs |
If it is midsummer and spreading, read up on chinch bugs instead. Those two get confused constantly, and the treatments have nothing to do with each other.
Why it shows up now
The fungus is temperature-driven. UF/IFAS says it becomes active “when temperatures drop below 80 degrees, usually between November and May,” and that it “often becomes a problem in fall.”
That timing is exactly why it catches people out. You spend the summer watching for insects, the weather finally breaks, everything feels easier, and that is the moment this particular problem wakes up.
It attacks all warm-season grasses but is “especially problematic in St. Augustinegrass and zoysiagrass,” which covers most of what is growing in Tallahassee yards.
The other ingredient is water. Excessive irrigation, heavy rainfall and high humidity all feed it. A lawn that is being watered on a timer through the autumn, or one sitting under a mat of wet leaves, is being handed the conditions the fungus needs.
The timing that actually matters here
This is the part worth writing on the calendar.
UF/IFAS guidance on preventive fungicide is regional, and North Florida is early: “In North Florida…applications should be made at the end of September. In South Florida, apply at the end of October.”
A preventive application is what it says. It works before symptoms appear, by protecting grass that has not been infected yet. Once you are looking at established patches you have moved from prevention to damage control, and control in the middle of an outbreak is considerably harder and less satisfying.
So if your lawn has a history of this, late September is the appointment, not November when you first notice circles.
What to do if it is already here
Prevention has sailed, but you can still stop making it worse.
- Water in the morning, and only when the lawn needs it. UF/IFAS is explicit about morning watering, because it lets the blades dry during the day. Evening irrigation leaves grass wet all night, which is precisely the condition the fungus wants.
- Back off the nitrogen. Apply “only slow-release nitrogen and do so sparingly.” The instinct when grass looks bad is to feed it. With this disease that instinct is wrong, because lush new growth going into cool weather is exactly what gets infected.
- Get debris off the turf. Wet leaves packed on the lawn hold moisture against the crown for weeks. Our leaf season here runs long, so this is not a one-off job.
- Mow it last, or clean the deck. Moving a mower straight from an infected patch across clean turf is a reasonable way to spread it around the yard.
- Do not panic about the dead look. The fungus attacks leaf sheaths. The plant frequently survives and regrows from the runners once it warms up.
The honest expectation
Large patch is a disease you manage rather than eradicate. Once a lawn has had it, the fungus is in the soil, and wet cool autumns will bring it back.
What changes the outcome is doing the small things on time: watering in the morning rather than at night, keeping the autumn feeding light and slow-release, clearing the leaves before they pack down, and treating preventively at the end of September if the lawn has a history. Get those right and most yards go from visible patches every year to the occasional mild one.
Not sure what you are looking at?
Half the difficulty with lawn disease is that several different problems produce brown grass, and the fixes actively conflict. Feeding a lawn with large patch makes it worse. Treating a fungus when the real issue is insects wastes a season.
We handle fertilization and weed control on a schedule across Leon County, and part of that is spotting this sort of thing while it is still small. Request a free quote or call and describe what you are seeing.
Symptom descriptions, temperature ranges and North Florida treatment timing are from UF/IFAS Extension. See Large Patch in Florida Lawns.
Common questions
Is large patch the same thing as brown patch?
They are caused by the same fungus, Rhizoctonia solani, and people use the names interchangeably, but UF/IFAS separates them. Large patch is the cool-weather version that shows up in autumn and spring on warm-season grass, which is what we get here. Brown patch more properly refers to a summer infection. If someone in Tallahassee is describing round expanding patches in November, they mean large patch whichever word they use.
Will the grass grow back where large patch killed it?
Usually yes, but slowly, and not until warm weather returns. The fungus attacks the leaf sheath rather than killing the runners outright, so the plant often survives and recovers once temperatures climb past the range the disease likes. Patches that were large or that got walked on all winter can stay thin and may need plugging in late spring. What you should not do is try to push recovery with nitrogen in the middle of winter, because that feeds the fungus rather than the grass.
Can I prevent large patch without spraying anything?
You can improve your odds a great deal. The disease needs moisture to establish, so the cultural side matters: water only when the lawn actually needs it and always in the morning so the blades dry during the day, keep nitrogen slow-release and sparing going into autumn, and do not let leaves or debris sit on the turf holding damp against it. On a lawn with no history of the disease that is often enough. On one that gets it every single year, culture alone usually is not.