Large Patch (Brown Patch) in St. Augustine Grass: How to Spot It and What to Do in Northeast Florida

Large patch does not mean the lawn is dead, and it is not fixed by more water or more fertilizer. Here is how to confirm it, how to separate it from look-alikes, and what University of Florida researchers recommend.

Seeing brown patches and not sure why? Ask RightWay to diagnose the cause before you treat.

Large Patch vs. Brown Patch: Why the Names Get Mixed Up

UF/IFAS calls the fall-through-spring disease large patch. It is caused by the fungus Rhizoctonia solani, and it is sometimes called brown patch. UF/IFAS points out that the name brown patch more accurately describes a separate turfgrass infection that occurs in the summer. Most Florida homeowners searching for brown patch in St. Augustine grass in the cooler months are looking at large patch.

Large patch affects all warm-season turfgrasses and is especially common in St. Augustine and zoysia, the two grasses seen most in Duval and St. Johns County neighborhoods.

When Large Patch Shows Up in Northeast Florida

UF/IFAS says the disease is usually seen from November through May, when temperatures drop below 80 degrees. It often starts in the fall, when cool temperatures and damp weather create the right conditions, and the patches keep growing into spring until the weather warms. In summer, the lawn may regrow and fill in the dead patches. If the disease is not managed, it returns the next fall.

Extended leaf wetness is the trigger. UF/IFAS lists rainfall, excessive irrigation and long periods of high humidity that keep leaves wet for 48 hours or more.

How to Identify Large Patch

• Shape: round patches that start about a foot across and can grow to several feet, sometimes forming rings.
• Color: yellow, then reddish brown, brown or straw-colored. The outer edge often looks darker, and sometimes orange, where the fungus is active.
• Center: often brown and sunken, though it may show new green growth as the turf recovers.
• Location: any part of the lawn that stays damp, including low spots, shaded areas and spots watered by overlapping sprinklers.

The Pull Test

Grab a few blades at the outer edge of a patch and tug. In large patch, the leaves pull easily from the stem, the base of the blade is dark and rotted, and it smells of rot. The fungus attacks the leaf base near the soil, and UF/IFAS notes it does not affect the roots.

Large Patch or Something Else? A Quick Comparison

If the patch keeps spreading in warm sunny weather, check for insects first using our guide to chinch bug damage in St. Augustine grass. If browning follows a frost, see our winter lawn care guide. Where the brown comes and goes with the weather, it can also be watering: during the current shortage, read our guide to lawn watering restrictions in Jacksonville and St. Johns County.

What Makes Large Patch More Likely

• Too much water, too late in the day: leaves that stay wet overnight are a major trigger.
• Too much quick-release nitrogen in the fall: UF/IFAS says to avoid excess nitrogen during disease periods and to use slow-release sources.
• Leaves left on the turf: a mat of leaves traps moisture against the grass.
• Poor drainage and shade: low spots and shaded corners stay wet longer.
• Disease history: large patch usually returns in the same spots each year.

What to Do About Large Patch

UF/IFAS says the best treatment is the same as the best prevention: lawn care that fits the season. The steps in order:

1. Water only when needed, and only in the morning. UF/IFAS recommends early morning, before 8 a.m. Under the one-day-a-week watering limit now in place in Duval and St. Johns County, set the timer for the early hours of your watering day and skip any cycle after rain.
2. Hold back on nitrogen. If you must feed, use slow-release nitrogen sparingly, within UF/IFAS rates for your grass and location.
3. Mow diseased areas last and clean the blades afterward. This keeps you from carrying the fungus to healthy turf.
4. Rake leaves and debris off the lawn. Drier turf is less hospitable to the fungus.
5. Be patient. If the lawn is otherwise healthy, UF/IFAS says regrowth should happen naturally over one or more growing seasons.

What About Fungicide?

If the cultural steps do not stop the spread, fungicides are available. UF/IFAS says they work best where the disease has appeared in previous years, and that the ideal timing is about two weeks before symptoms usually show up, which in North Florida is typically the end of September. Applications made after symptoms appear will stop the fungus from growing but may need to be repeated through the winter until the grass starts growing again.

Always read the product label before use, since the label is the law, and treat only the affected area unless a professional recommends otherwise. A wrong diagnosis wastes the product, because fungicide does nothing for insects, root rot or herbicide injury.

How to Prevent Large Patch Next Fall

• Mark where patches appeared this year, since they usually return in the same places.
• Keep irrigation to the schedule the lawn needs and run it before sunrise.
• Avoid late-season quick-release nitrogen.
• Keep leaves off the lawn through the fall and winter.
• Improve drainage in low spots and trim back shade where it makes sense.
• Ask a lawn professional about timing a preventive application for your property. RightWay's lawn service is built around Northeast Florida timing and conditions, and the team can tell cold damage from fungus and pests before building a plan.

When to Call a Professional

• Patches keep spreading after you change watering and feeding.
• You cannot tell whether it is fungus, insects or root rot.
• The same areas fail every fall.
• A large share of the lawn is affected.

If you are in Nocatee, Ponte Vedra or Julington Creek, where irrigation clocks are often controlled by the community, ask your HOA to confirm the controller is not running in the evening.