Large Patch Identification & Treatment

Large circles in a zoysia or St. Augustine lawn during spring or fall are almost always large patch. Treat preventively in fall when soil hits 70°F on the way down, and stop nitrogen well before that.

• Patch shape: circular to irregular rings, commonly 2 to 20 feet across, often with green recovering turf in the center.
• Margin: a distinct orange or bronze band of recently infected turf at the expanding edge.
• Leaf sheath: pull a blade at the margin — the sheath is dark, water-soaked, and rotted, and the leaf detaches easily.
• Roots: generally intact, which distinguishes it from insect damage.
• Timing: appears in spring during green-up or in fall as the lawn slows down, not in mid-summer.

1. Stop nitrogen at least six weeks before the average first frost; late nitrogen is a major severity driver.
2. Water only in the early morning, and reduce total irrigation as the lawn slows in fall.
3. Improve surface and internal drainage in low areas where patches recur.
4. Aerate compacted zoysia and dethatch when thatch exceeds about half an inch.
5. Raise mowing height slightly in fall to reduce stress, then cut back at dormancy.
6. Increase airflow and light in shaded areas that stay wet into mid-morning.

Preventive fall application is the standard approach. Apply when two-inch soil temperatures fall to about 70°F, with a second application 21 to 28 days later if the lawn has a strong history. Azoxystrobin and propiconazole are the common homeowner-available options. Water the product in lightly if the label directs, since the target tissue is at the leaf sheath and crown rather than the leaf tip.

Spring applications can slow an active outbreak but rarely reverse the visible damage. Once the lawn is growing at summer temperatures, recovery happens on its own.

Zoysia and St. Augustine spread by stolons and rhizomes, so patches usually fill in during summer without replanting. Recovery is slow in zoysia — a large patch scar can take most of a season to close. Centipede recovers slowest of the three. If a patch has not begun filling by mid-summer, plug or sod that area.

• Waiting for spring symptoms before treating, when the fall window has already closed.
• Applying a late-fall 'winterizer' nitrogen feed to a warm-season lawn.
• Continuing summer irrigation volumes into cool fall weather.
• Assuming the circles are grubs and applying an insecticide.
• Replanting damaged areas in spring before natural recovery has had a chance.

This guide provides the science behind the following recommendation engine tasks.

• Fall Preventive Fungicide
• Late-Season Nitrogen Cutoff
• Disease Prevention Watering Window

Put a soil thermometer in the lawn each fall. When the two-inch reading drops to 70°F, that is your application date — not the day you first see a circle.