When to Apply Fungicide for Large Patch: Start at 70°F in Fall

Quick Answer: When Should You Apply Fungicide for Large Patch?

Make the first large patch application in fall, once soil at 2 inches falls to 70°F and holds there for 5 days, and make the second 3 to 6 weeks later while soil stays above 50°F. Your schedule shows the window as a falling 50-70°F band. Fix the cultural causes first: no nitrogen in the 6 weeks before dormancy, water only when the lawn needs it, and drain the wet spots. NC State Extension starts St. Augustine and centipede earlier, at 80°F, which this guide covers below.

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Large patch shows up in spring as rings of brown and orange grass in zoysia, St. Augustine and centipede lawns. By then the infection is months old. The fungus gets into the plant the previous fall, as the soil cools, and fall is when a fungicide does the most good.

That makes large patch a timing problem. A homeowner granule protects for a few weeks (its label reapplies every 14 to 28 days), so a spray in August, before soil falls to 70°F, wears off before infection starts on zoysia. (St. Augustine and centipede are the exception: NC State starts them at 80°F, in late August or early September.) A spray on visible patches comes too late: the University of Missouri says curative applications are less effective.

This guide covers the fall trigger and how the sources differ on it, where large patch occurs, the second application, the cultural steps that come before any spray, and the two fungicides that fit a homeowner program.

What Large Patch Is and Why Soil Temperature Times It

Large patch is caused by the fungus Rhizoctonia solani. The University of Arkansas calls it a disease of warm-season turf that does its damage in spring and fall, with zoysia, St. Augustine and centipede all highly susceptible. NC State Extension ranks centipede as the most susceptible lawn grass, followed by zoysia and then St. Augustine. Bermuda is rarely affected and recovers quickly. Fescues and bluegrasses are immune. University of Georgia Extension says all warm-season grasses are susceptible in Georgia, with zoysia and centipede most often hit in the Piedmont and St. Augustine and centipede on the Coastal Plain.

Patches run from 1 foot to more than 3 feet across, per NC State, and show tan, yellow, orange or red lesions on the leaf sheaths. Symptoms appear in fall and again in spring, after stretches of cool, wet weather.

The University of Missouri explains why the calendar matters: infection takes place in early fall, when the fungus moves down to the base of the plant inside the leaf sheath, so fungicide has to be in place then, not when symptoms show. Soil temperature is the signal that the fungus is starting that work: NC State says large patch begins to develop when soil temperatures decline to 70°F in the fall.

The Trigger: Soil Falling to 70°F

Every source agrees on fall and on a falling temperature near 70°F. They differ on the grass, the number of days, and whether to measure the soil or the thatch layer above it.

None of these sources states a soil depth. SoilTemps reads soil at 2 inches, the shallowest depth the monitoring networks report.

NC State Extension gives the most specific rule: start zoysia when soil temperatures decline to 70°F for 5 or more consecutive days. Clemson Cooperative Extension applies 70°F to all three grasses after 2 to 3 days. The University of Arkansas and the University of Missouri also use 70°F.

The one real split is St. Augustine and centipede. NC State starts those two at 80°F, which its 2022 trial review places in late August or early September in Raleigh. Clemson and Arkansas do not make that distinction.

University of Georgia Extension and University of Missouri Extension read the thatch, the layer of dead stems and roots between the blades and the soil. Their figures (below 69.8°F; 70 to 75°F) land on the same point in the season as the 70°F soil trigger.

The schedule keeps the task open while soil stays in the 50-70°F band and closes it once soil holds below 50°F, because NC State repeats applications only while soil temperatures remain above 50°F.

Where Large Patch Occurs

Large patch follows the warm-season grasses. The University of Arkansas calls it a disease of warm-season turf, University of Georgia Extension says all warm-season grasses are susceptible in Georgia, and UF/IFAS Extension says it attacks all warm-season turfgrasses in Florida, St. Augustine and zoysia most of all. NC State ties symptoms to cool, wet weather in spring and fall.

Your schedule decides whether to show the task from your area's normal summer and winter temperatures and its climate type, and shows it where the winters are mild enough and the summers warm enough for warm-season lawns. Hot deserts and the dry West are left out. Your soil readings then set when the task opens and closes.

Southern and Warm-Season Lawns

Most of the sources come from this region, from Arkansas and the Carolinas to Georgia and Florida, and they name zoysia, St. Augustine and centipede. University of Georgia Extension sees zoysia and centipede hit most often in the Piedmont, and St. Augustine and centipede on the Coastal Plain.

The South treats later in fall. Clemson's first-application dates for South Carolina run from October 15 in Clemson, Greenville and Rock Hill to October 25 in Charleston and Beaufort. UF/IFAS Extension times Florida by the calendar: the end of September in North Florida and the end of October in South Florida. The schedule closes the task at the end of December even where soil stays above 50°F.

Transition Zone

In the transition zone, where warm-season and cool-season lawns grow side by side, the sources write about zoysia: the University of Missouri and Kansas State University both cover large patch on zoysia lawns. Missouri times zoysia for early to mid-September, when soil first dips below 70°F, and NC State puts the 80°F start for St. Augustine and centipede in late August or early September in Raleigh.

Many transition-zone cities default to a cool-season schedule. The task appears on both schedules there, so a zoysia lawn in one of those cities still gets it. If your lawn is tall fescue or bluegrass, the task does not apply to you: NC State says those grasses are immune.

Cool-Season Regions

Fescue and bluegrass lawns do not get large patch: NC State says those grasses are immune.

The Second Application, and Whether to Spray in Spring

One fall application rarely lasts the season. NC State Extension says two well-timed applications may give season-long control. The sources disagree on the gap between them:

Spring spraying has thin support. The University of Arkansas is the only source with a spring number: start when soil temperatures are consistently above 50°F, which usually matches about 50 percent green-up, and repeat at four-week intervals if the weather stays wet. Kansas State University found spring applications are not as effective as fall applications, and NC State Extension says fall applications are the most critical, and that spring applications may be necessary in cool, wet springs as a complement to a strong fall program. Clemson includes one spring application once the lawn has begun to green up, with no temperature given. Put your effort into the fall program. Add one spring application, at the Arkansas trigger, only if your lawn has a history of severe large patch.

Cultural Controls Come First

Every source puts these ahead of fungicide. Do them before you spend money on a spray.

Step 1: Stop Fall Nitrogen

The University of Missouri warns that nitrogen in fall or spring, when zoysia growth is slow, can tip the scales in favor of the fungus. NC State Extension says not to apply nitrogen to warm-season grasses within 6 weeks before fall dormancy, or within 3 weeks after spring green-up begins. Clemson sets the South Carolina cutoff at August 15 in the Upstate and mid-state and September 1 on the coast, and warns that most winterizer fertilizers contain nitrogen too. UF/IFAS Extension says to use only slow-release nitrogen, sparingly. Time your feeding with the warm-season fertilization schedule.

Step 2: Water Less, and Only in the Morning

NC State lists over-watering among the conditions that favor large patch, and says to irrigate only as needed to prevent severe drought stress in fall and spring. Clemson says to water no more than once a week in spring and fall, always in the early morning. The irrigation timing guide covers the morning watering window.

Step 3: Fix Drainage and Compaction

Poorly drained areas are especially susceptible, per the University of Missouri. NC State recommends subsurface drainage where water stands, and aeration to keep the soil draining. University of Georgia Extension adds that core aeration improves drainage and air movement around the shoots and roots.

Step 4: Mow at the Right Height and Control Thatch

Mowing too low and a thick thatch layer both favor the disease, according to Clemson. NC State says to mow at recommended heights and power rake or vertical mow as needed. Do that work in summer: Missouri recommends core cultivation or verti-slicing in June or July and warns against cultivating in early spring or whenever the disease is active. The aeration timing guide covers warm-season aeration dates.

Fungicides for Large Patch

If the lawn has had large patch before and the cultural steps are in place, a preventive fungicide is the next step. The University of Missouri recommends treating only areas with a history of the disease. University of Georgia Extension and the University of Missouri both warn that homeowner fungicides are weaker than professional ones, so expect fewer patches, not a clean lawn.

Clemson Cooperative Extension rates the granular fungicides it lists for large patch. Scotts DiseaseEx (azoxystrobin) applied together with BioAdvanced Fungus Control for Lawns (propiconazole) rates Excellent. An azoxystrobin granule alone (Heritage G) and the propiconazole lawn product alone each rate Good. The University of Arkansas also recommends combining two fungicide groups over a single active ingredient. Azoxystrobin and propiconazole are in different groups (Arkansas lists the pair among its top performers), so using both together follows that advice, as Clemson's top rating does. The lawn disease by temperature guide explains fungicide groups and how to rotate them.

1. Azoxystrobin Granules (Best for All Three Grasses)

Common Brand Name: Scotts DiseaseEx

The DiseaseEx label lists Rhizoctonia large patch at 2 to 4 lb per 1,000 sq ft, with one or two applications in fall, reapplied at 14 to 28 day intervals. It goes down with a spreader. The label says to water for 15 to 20 minutes after application unless rain is expected within 24 hours, and Clemson asks for at least ½ inch of water right after a granular fungicide. Put down ½ inch. People and pets may re-enter after application, per the label.

Best Used For: St. Augustine and centipede lawns, and any homeowner without a sprayer.

2. Propiconazole Liquid (Best for Zoysia)

Common Brand Name: Select Source Propiconazole 14.3

The label names large patch on zoysia only: 3 to 4 fl oz per 1,000 sq ft, one application in early fall (mid-September to mid-October) before symptoms develop, and it tells you to ask your local extension office for the best date in your area. It does not name St. Augustine or centipede, so do not use it for large patch on those lawns; use the azoxystrobin granules instead. For soil-borne diseases the label allows watering in after application. NC State says to spray fungicides for large patch in at least 2 gallons of water per 1,000 sq ft, and Arkansas suggests about 2 gallons with a soil surfactant. That takes a pump sprayer.

Best Used For: Zoysia lawns, as the second fungicide group alongside azoxystrobin.

Common Mistakes

Waiting for symptoms. The rings you see in spring were infected the fall before. A spray on visible patches is a curative application, and Missouri says curative applications are less effective. Treat in fall on lawns with a history of the disease.

Spraying too early. A first application in August, before soil falls to 70°F (or 80°F for St. Augustine and centipede), wears off before infection starts.

Feeding in fall. A winterizer on zoysia or St. Augustine feeds the fungus. Stop nitrogen 6 weeks before dormancy.

Watering at night or every day. NC State lists over-watering among the conditions that favor large patch. Water only when the lawn needs it, in the early morning.

Using a zoysia-only label on St. Augustine. The propiconazole label covers large patch on zoysia only. Read the disease table on the label before you buy.

Treating a fescue lawn. Tall fescue and bluegrass are immune. If your transition-zone lawn is fescue, the large patch task on your schedule is not for you.

Track Your Local Soil Temperatures Today

The fall trigger depends on how fast your own soil cools, and that varies by weeks between neighboring regions and between one fall and the next. A date borrowed from a neighbor two states away misses it.

At SoilTemps.com we track 2-inch soil temperatures from more than 300 USDA SCAN and NOAA USCRN stations, and cities far from a station get a Modeled reading. Your city's lawn care schedule shows when the large patch task is coming up, when it opens, and when it closes for the season.

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Related Guides

• Lawn Fungus by Temperature
• Warm-Season Fertilization Schedule
• Irrigation Timing by Soil Temperature
• Aeration Timing
• When to Apply Pre-Emergent in Fall
• Winter Dormancy Care