Quick Answer: When Should You Apply Fungicide for Summer Patch?
Apply a preventive fungicide for summer patch in spring, once soil at 2 inches reaches 65°F and holds there for 5 days, then repeat every 28 to 30 days. Purdue, Nebraska, Rutgers, Penn State and Kansas State all time the first spray to 65°F, and your schedule opens the task after 5 days at that temperature. It applies to Kentucky bluegrass and fine fescue lawns; tall fescue is not susceptible. Start with the cultural steps: ammonium-based fertilizer, no heavy spring nitrogen, a 3-inch mowing height and deep, infrequent watering. Purdue treats spraying a home lawn as a last resort.
Quick Answer
Check your local 2-inch soil temperatures now
Enter your city or ZIP code to see real-time soil temperature data from the nearest USDA or NOAA monitoring station.
Summer patch shows up from June through August as rings and crescents of straw-colored grass in a Kentucky bluegrass lawn, often with a green tuft in the middle. Summer heat brings the patches out, but the roots in those rings were infected in spring, when the soil first warmed.
So the spray, if a lawn needs one, goes down in spring, while the lawn still looks healthy. For a home lawn, Purdue puts the fertilizer, mowing and watering habits that keep roots strong ahead of any spray.
This guide covers how summer patch works, the 65°F soil trigger and how the sources count the days, where the disease shows up, the repeat applications, the cultural steps to take before any fungicide, and the two homeowner fungicides whose labels name summer patch.
What Summer Patch Is and Why Soil Temperature Times It
Summer patch is a root disease caused by the fungus Magnaporthiopsis poae (older sources call it Magnaporthe poae). Purdue Extension names its hosts as Kentucky bluegrass and annual bluegrass (BP-115) and Kentucky bluegrass and fine fescues (BP-218), and says it is most severe on Kentucky bluegrass. Nebraska Extension lists all three as primary hosts. Purdue says perennial ryegrass and tall fescue are not susceptible.
The fungus attacks roots, crowns and rhizomes. Purdue says it may infect and colonize roots once soil temperature exceeds 65°F, and that this root infection often happens in spring, before any symptoms. The grass carries on looking normal until summer heat and drought ask more of the roots than the damaged ones can give. Then patches appear: Purdue describes them as 6 inches to 3 feet across, straw-colored and sunken, with dark, rotten roots and rhizomes that pull up easily. Kansas State University adds that the fungus can survive several years in the soil and cause repeat damage in the same spots.
Penn State's Turfgrass Pest Diagnostic Lab says the disease is most common in turf stands three years old or older, and Nebraska sees it most in full sun and in stressed areas near sidewalks and driveways.
That gap between infection and symptoms is why the calendar works against you. By the time you can see summer patch, the time to prevent it has passed, and soil temperature tells you when that time begins.
The Trigger: 65°F at 2 Inches in Spring
The sources agree on the number. They differ on the depth, the time of day they read the soil, and how many days it has to hold.
| Source | Soil temperature | Depth | When read, and how long |
|---|---|---|---|
| Nebraska G1913 (2009) | Reaches 65°F | 2 inches | Mid-afternoon, 5 consecutive days |
| Penn State Turfgrass Pest Diagnostic Lab | At least 65°F | 2 inches | 2 PM, three to four consecutive days |
| Rutgers (2017) | Daily maximum of 65°F | Not stated | 5 consecutive days |
| Purdue BP-115 (2016) | Daily maximums averaging 65°F or higher | 3 inches | Several consecutive days |
| Purdue BP-218 (2024) | Reaches 65°F in spring | Not stated | Not stated |
| Kansas State MF3239 (2015) | Consistently above 65°F | 2 inches | Not stated |
Nebraska Extension gives the most complete rule: begin preventive treatments in May, when soil temperature at a 2-inch depth in mid-afternoon reaches 65°F for 5 consecutive days. Rutgers uses 5 consecutive days with a soil temperature maximum of 65°F, and Penn State uses three to four days of 65°F or more at 2 PM.
Purdue adds a warning against going early: fungicide sprays aimed at summer patch will be ineffective if applied before the 65°F threshold is reached, because the fungus is not yet active.
The sources that say when to read the soil all read the warm part of the day: Rutgers and Purdue BP-115 use the daily maximum, Penn State a 2 PM reading and Nebraska a mid-afternoon one. SoilTemps reports the daily average at 2 inches, which runs below the afternoon high. So your schedule opens the task a little later than a daily-high reading would. When the task opens, apply.
Your schedule opens the summer patch task once 2-inch soil has held at 65°F or above for 5 days and is still warming. That is the time for the first application on a lawn with a history of summer patch. Do not spray before it opens: Purdue says a spray applied before soil reaches 65°F is ineffective.
Where Summer Patch Shows Up
Summer patch goes where its host grasses grow. The sources behind this guide come from Indiana, Nebraska, Kansas, Pennsylvania and New Jersey, and Kansas State University says that in Kansas the disease occurs in Kentucky bluegrass lawns. None of the sources lists a warm-season grass as a host.
The bad years are the hot, dry ones. Purdue ties extensive outbreaks to severe heat and drought stress during the summer, and Kansas State says symptoms usually wait until the turf is stressed by heat and drought.
Your schedule shows this task on cool-season lawns, where the soil record of your nearest station shows a growing season long enough for a cool-season lawn. It opens when your own 2-inch soil reaches the trigger, usually between April and June; if your soil gets there earlier, the task opens then.
Kentucky Bluegrass and Fine Fescue Lawns
These are the lawns the task is for. The timing shifts with your soil. Nebraska plans the first application for May and the repeat for June. Purdue's BP-218 puts infection in May and symptoms in June through August. At the Rutgers research farm in North Brunswick, New Jersey, the 2017 trigger came on May 1, the fifth straight day the soil maximum reached at least 65°F.
Tall Fescue Lawns
Purdue says tall fescue is not susceptible, so a tall fescue lawn needs no summer patch fungicide even though the task appears on its cool-season schedule. If your lawn is a mix, the bluegrass in it is what is at risk.
Where Spring Soil Warms Late
The task's calendar runs from April through June. Where spring soil does not reach 65°F before the end of June, the task closes for the season without opening.
If summer patch has hit your Kentucky bluegrass or fine fescue lawn before and your schedule does not show the task this year, time it yourself: make the first application once your 2-inch soil has held at 65°F for 5 days, and repeat every 28 to 30 days.
Repeat Applications
One spring spray does not cover the season. The sources space the repeats about a month apart, and the labels allow shorter gaps:
| Source | Repeat spacing |
|---|---|
| Purdue BP-115 | Several applications at 28-day intervals |
| Nebraska G1913 | Repeat 30 days after the first (May, then June) |
| Kansas State MF3239 | A second application as the fungicide label recommends |
| The two product labels in this guide | Every 14 to 28 days, depending on product and rate |
Penn State adds a limit for one fungicide group: DMI fungicides, the group propiconazole belongs to, should go down at summer patch rates no later than early June, to limit excessive growth regulation and injury to the turf. Purdue warns that using the same fungicide class over and over for summer patch can breed resistant strains of other lawn diseases, such as dollar spot. For how fungicide groups work and how to alternate them, see the lawn disease by temperature guide.
Before the window: aerate, even with solid tines, and water before and after you treat. Purdue says both may help the fungicide reach the roots.
Application 1: when your schedule opens the task (2-inch soil at 65°F or above for 5 days).
Application 2: 28 to 30 days later. If the first was propiconazole and the second date falls after early June, use azoxystrobin for the second. Penn State recommends two fungicide groups for preventive treatment: DMI fungicides such as propiconazole, and QoI fungicides, the group azoxystrobin belongs to. The switch gives you that second group.
Get it to the roots: this is a root disease. Purdue says to water the fungicide into the soil profile, and Kansas State says to use enough water to carry it into the root zone.
Cultural Controls for Summer Patch
Purdue says control of summer patch is difficult and that relying on fungicides alone is always expensive, with results that are often inconsistent. Nebraska says the disease is managed primarily through cultural practices. Put these in place first.
Step 1: Feed Lightly in Spring, With Ammonium Nitrogen
Purdue says to avoid excessive nitrogen in spring, particularly nitrate-based fertilizers, which can make the disease worse. Kansas State suggests putting 75 percent of a Kentucky bluegrass lawn's yearly nitrogen down in fall and 25 percent in spring, with the spring feeding in a slow-release form. Plan the year's feedings with the cool-season fertilization schedule.
Step 2: Lower Soil pH With Acidifying Fertilizer
Purdue recommends lowering soil pH to 5.5-6.0 by using ammonium-based fertilizers, and Penn State aims for a pH around 6.0 with acidifying fertilizers, with lime applied sparingly and only on a soil test's advice. Kansas State notes that ammonium sulfate can reduce severity, but that high-pH irrigation water can counter the acid in the fertilizer. Purdue also says manganese sulfate at 6 lb per acre in spring may suppress the disease. Test the soil before you change its pH.
Step 3: Mow at 3 Inches
Purdue recommends keeping home lawns mowed at 3 inches, which eases the demand on a damaged root system. Penn State says a low mowing height increases severity, Kansas State sets a floor of 2 inches, and Nebraska raises the mowing height in July and August.
Step 4: Water Deeply, Less Often
Purdue lists deep, infrequent irrigation among the practices that relieve summer stress, and Penn State says frequent light irrigation increases severity while wet soil from poor drainage or overwatering promotes infection. Once patches have appeared, the advice changes: Purdue's BP-218 switches to frequent light watering to minimize stress, Nebraska uses light, frequent watering in dry summer spells to reduce heat stress, and Kansas State says watering in the afternoon can cool the plants. How much and how often to water is in the irrigation timing guide.
Step 5: Aerate and Reduce Thatch
Kansas State says lawns with a history of summer patch should be dethatched or core aerated every year. Purdue recommends core or deep-tine aeration in fall and spring to promote deep rooting, and BP-218 adds vertical mowing and topdressing to cut thatch. Penn State recommends aerating only when no symptoms are showing. Purdue also notes that aeration can carry infected root debris to clean parts of the lawn, so aerate the old patches last. See the aeration timing guide for cool-season dates.
Step 6: Change the Grass Where It Keeps Coming Back
Purdue recommends overseeding lawns with a history of summer patch with turf-type tall fescue, which is not susceptible. Nebraska suggests aerating in late August and overseeding with perennial ryegrass and an improved Kentucky bluegrass blend, or renovating with tall fescue. If you keep bluegrass, Kansas State lists moderately resistant older cultivars (Adelphi, Admiral, America, Baron, Bristol, Challenge, Columbia, Eclipse, Majestic and Monopoly), and both Kansas State and Purdue point to the National Turfgrass Evaluation Program trials for newer ones. The fall overseeding guide covers the seeding window.
Purdue Extension tells residential lawn owners to consider fungicide application only if other options have been thoroughly exhausted, and then to have it done by a custom spray applicator. Nebraska Extension says fungicides should only be considered if other practices fail. If you do treat, keep the steps above going: Kansas State says chemical control is not completely effective, but can reduce disease when combined with them.
What you need
- Granules, for a spreader: Scotts DiseaseEx (azoxystrobin)
- Liquid, needs a pump sprayer: Select Source propiconazole 14.3
Fungicides for Summer Patch
If you treat the lawn yourself instead of hiring an applicator as Purdue advises, these are the two homeowner products whose labels name summer patch. A preventive fungicide is for a bluegrass or fine fescue lawn that has had summer patch before, once the cultural steps are in place. Purdue explains why results vary: summer patch is a root disease, and very little fungicide finds its way underground. Watering it in is what gets it there.
Nebraska Extension, using a University of Kentucky efficacy table, rates azoxystrobin 4 (excellent control) and propiconazole 3+ (between the good-to-excellent and excellent ratings) for summer patch. Kansas State's 2015 version of the Kentucky table rates azoxystrobin 4 and propiconazole 3.
1. Azoxystrobin Granules (Best Rated, No Sprayer Needed)
Common Brand Name: Scotts DiseaseEx
The label lists summer patch at 2 to 4 lb per 1,000 sq ft, reapplied at 14 to 28 day intervals, using the shorter interval and higher rate when disease conditions last. Spread it with a spreader, then water for 15 to 20 minutes unless rain is expected within 24 hours. The label allows no more than 37 lb per 1,000 sq ft in a year, so two or three spring applications fit well inside it. People and pets may re-enter after application, and the label allows it after seeding or at seed germination, which suits a lawn you are overseeding with tall fescue.
Best Used For: A bluegrass or fine fescue lawn with a history of summer patch and no sprayer, and the second application in a program that started with propiconazole.
Scotts DiseaseEx Lawn Fungicide (azoxystrobin 0.31%, granular, 10 lb)
Azoxystrobin granules whose label lists summer patch at 2 to 4 lb per 1,000 sq ft, reapplied every 14 to 28 days. Water in for 15 to 20 minutes unless rain is due within 24 hours. Nebraska Extension rates azoxystrobin excellent for summer patch.
2. Propiconazole Liquid (Best for Larger Lawns With a Sprayer)
Common Brand Name: Select Source Propiconazole 14.3
The label lists summer patch at 4 fl oz per 1,000 sq ft every 28 days or 2 fl oz every 14 days, beginning in April, with no more than 16 fl oz per 1,000 sq ft in a calendar year. Because summer patch is soil-borne, the label lets you water the spray in afterward. Keep people and pets off until the spray dries. Propiconazole is a DMI fungicide, so follow Penn State's advice and finish the propiconazole applications by early June.
Best Used For: Larger bluegrass lawns, owners who already have a pump sprayer, and the first application in a program that rotates to azoxystrobin.
Select Source Propiconazole 14.3 Fungicide (pint concentrate)
Propiconazole concentrate whose label lists summer patch at 4 fl oz per 1,000 sq ft every 28 days or 2 fl oz every 14 days, beginning in April. Water in after spraying so it reaches the roots. Nebraska Extension rates propiconazole 3+ for summer patch.
Common Mistakes
Spraying the rings in July. The roots in those rings were infected in spring. Purdue says sprays applied after symptoms occur have very limited effects.
Spraying before the window opens. Purdue says a summer patch spray applied before soil reaches 65°F is ineffective. Wait for your schedule to open the task.
Skipping the watering-in. A fungicide left on the blades does little against a fungus in the roots. Water it in the same day.
A heavy spring feeding of nitrate nitrogen. Purdue says nitrate-based fertilizers in spring can make the disease worse. Feed lightly, with ammonium.
Short mowing and frequent light watering. Penn State says both increase severity. Mow at 3 inches and water deeply.
Spraying tall fescue. Tall fescue is not susceptible, according to Purdue. The task is for Kentucky bluegrass and fine fescue.
Track Your Local Soil Temperatures Today
The 65°F trigger moves with each spring's weather and with where you live, so a fixed calendar date can put the first spray down before the fungus is active or after the roots are already infected.
SoilTemps.com reports the 2-inch soil temperature for your city from the nearest of more than 300 USDA SCAN and NOAA USCRN stations, or a Modeled reading where no station is close by. Your city's lawn care schedule follows the summer patch task through spring, from coming up to open to closed for the year.
Has your soil reached 65°F?
Enter your city or ZIP code to check your local 2-inch soil temperature and whether your spring summer patch window has opened.