Lawn Fungus: Identify 16 Lawn Diseases and Choose the Right Fungicide

Key takeaways

• Purdue Extension says brown patch fungicides “should not be necessary for residential lawns” because the fungus does not kill crowns or roots, so turf regrows when weather turns (Purdue BP-106).
• Weather sets the calendar: brown patch needs dew periods over 10 hours with nights above 65°F, Pythium blight over 14 hours with evenings averaging 68°F or more (Purdue BP-109).
• Nitrogen cuts both ways: dollar spot, red thread and rust are worse on hungry turf (Purdue fixes red thread with 0.2 lb N per 1,000 sq ft), while brown patch, Pythium and large patch flare with excess nitrogen (Purdue BP-104; Arkansas FSA7527).
• Every homeowner lawn fungicide in Arkansas’s 2026 products guide is FRAC group 11 (azoxystrobin), 3 (propiconazole, myclobutanil) or 1 (thiophanate-methyl), plus copper and potassium bicarbonate; Ohio State rates resistance concern high for groups 1, 3 and 11 (UADA MP154; Ohio State).
• Rule out look-alikes before buying anything: grubs matter above about 5 per square foot (Purdue E-271), and dog-urine spots smell of ammonia when the dead grass is sealed in a plastic bag (WSU HortSense).

What does lawn fungus look like?

Lawn fungus shows up as a field pattern you see from 10 feet away and a sign you see up close. Purdue’s diagnostic guide sorts the patterns into circular patches, frogeyes or rings, linear streaks and diffuse thinning (Purdue BP-124). The close-up sign settles it: cottony mycelium at dawn, red threads, orange pustules, leaf lesions with dark borders, or black, rotted roots.

Read the patch edge, not the dead center, where the fungus has already moved on. The table below lists 16 diseases that extension pathologists profile for U.S. lawns, the grasses each attacks and the sign that separates it from its look-alikes. Grass names follow our Turf and Trees section; if you do not know your species, identify it first, because most diseases attack only a few grasses.

Swipe the table sideways to see every column.

Disease	Grasses it attacks	What you see from 10 ft	Sign up close	Source
Brown patch	Tall fescue, perennial ryegrass; all cool-season grasses	Tan to brown circles 6 in to several ft across; leaves stay upright	Tan, irregular leaf lesions with a dark border; gray “smoke ring” at the edge on short turf	NC State; Purdue BP-106
Large patch	Zoysiagrass; bermudagrass less often	Tan circles up to 20 ft across in fall and at spring green-up	Orange border on active patches; lower leaves die as sheaths are killed	Arkansas FSA7527
Dollar spot	All warm- and cool-season lawn grasses	Sunken straw spots under 1/2 in to over 4 in, often merging	Straw lesions with a red-brown margin; white cobweb growth at dawn	UGA C1091; Purdue BP-105
Pythium blight	Perennial ryegrass, rough bluegrass; tall fescue and Kentucky bluegrass rarely	Small greasy, water-soaked patches that merge in days, often in low spots	Cottony white mycelium in the morning; dead turf mats down	Purdue BP-109
Summer patch	Kentucky bluegrass, annual bluegrass	Circular or oval orange-brown patches and frogeyes from late July	Sparse, dark, rotted roots	Purdue BP-115
Necrotic ring spot	Kentucky bluegrass, annual bluegrass	Clustered gray-tan patches 6 to 8 in, later rings and frogeyes	Stunted, dark roots; tip die-back	Purdue BP-116
Red thread	Kentucky bluegrass, perennial ryegrass, tall fescue	Tan or pink patches 4 to 8 in in spring and fall	Red, antler-like threads on leaf tips	Purdue BP-104
Rust	Kentucky bluegrass, perennial ryegrass	Yellow-green cast, worst in shade and along foundations	Orange pustules; orange dust on shoes and mowers	Purdue BP-110
Gray snow mold	All cool-season grasses	Circular patches 6 to 12 in at snowmelt	Gray mycelium; tiny black or red-brown sclerotia in dead leaves	Purdue BP-101
Pink snow mold (Microdochium patch)	All cool-season grasses	Circular, matted patches, with or without snow	White to pink mycelium on leaves in cool, wet weather	Purdue BP-102
Leaf spot and melting out	Kentucky bluegrass, perennial ryegrass, tall fescue	Diffuse thinning, off-color areas	Purple-brown leaf lesions; no mycelium on leaves	Purdue BP-103
Gray leaf spot	Perennial ryegrass, tall fescue, St. Augustinegrass	Blue-gray, thin turf that looks like drought	Gray mold on leaves after an overnight bag test	Purdue BP-107; NC State
Fairy ring	All lawn grasses	Dark green bands or arcs under 1 ft to over 100 ft; mushrooms after rain	Ring persists in the same spot year after year	Purdue BP-113
Slime mold	Any grass, mostly taller-mown	Yellow, orange, purple or gray crust on blades for 1 to 2 weeks	Spore masses that turn gray and powdery; grass underneath is unharmed	Purdue BP-112
Spring dead spot	Bermudagrass	Sharp circular dead patches as the lawn greens up in spring	Black roots and stolons	Purdue BP-120
Take-all root rot	All warm-season grasses, mostly St. Augustinegrass	Irregular yellow patches a few inches to a few feet that thin out	Short, black, rotted roots; black strands on stolons	UF/IFAS LH079

Mushrooms on their own are a fruiting body, not a disease of the grass; our guide to lawn mushrooms covers which ones are poisonous and why fungicides do not stop them. Fairy ring belongs in the table because Purdue notes it can kill grass in bands and leave soil that repels water (Purdue BP-113).

Is it fungus, grubs, dog urine or drought?

Four problems make brown patches in lawns, and only one of them responds to fungicide. A tug test, a one-square-foot dig, a sniff test and a look at the whole lawn separate them. UF/IFAS lists diagnosis among its reasons homeowners are discouraged from buying fungicides: each product is made for specific diseases, and treatments differ completely by cause (UF/IFAS PP154).

1. 1Does the turf lift like carpet, with C-shaped white grubs in the top 2 to 3 inches of soil?

   YesGrubs. Count per square foot; most turf tolerates up to 5 (Purdue E-271). See our grub guide.

   NoGo to the next question

2. 2Is it a round spot a few inches wide with a dark green ring, and does dead grass sealed in a bag smell of ammonia?

   YesDog or animal urine (WSU). Water the spot heavily and reseed it; no fungicide.

   NoGo to the next question

3. 3Is the whole lawn blue-gray with folded blades, and do footprints stay visible?

   YesDrought stress (UF/IFAS LH025). Water deeply before sunrise and recheck in a week.

   NoGo to the next question

4. 4Do leaves at the patch edge show lesions, red threads, orange pustules or cottony growth at dawn?

   YesA leaf disease. Match the sign to the ID table, then fix water and nitrogen first.

   NoGo to the next question

5. 5Are the roots short, dark and rotted under a patch or ring that returns each year?

   YesA root disease such as summer patch, necrotic ring spot, spring dead spot or take-all root rot. Get a lab diagnosis; sprays must go on before symptoms.

   NoSend a sample to your state plant diagnostic lab before buying a fungicide (UF/IFAS PP154).

Source: Purdue E-271 and BP-124; WSU HortSense; UF/IFAS LH025, LH079 and PP154

Test	Result	Points to	Source
Tug a handful of grass at the patch edge	Mat lifts like carpet, roots chewed off	White grubs	Purdue E-271
Cut and lift 1 sq ft of sod, 2 to 3 in deep	More than 5 C-shaped grubs per sq ft	Possible grub damage; most turf tolerates up to 5	Purdue E-271
Seal dead grass in a plastic bag for a few hours, then smell	Ammonia odor; dark green ring around a spot a few inches wide	Dog or other animal urine	WSU HortSense
Look at the whole lawn, then walk on it	Folded blades, blue-gray tint, footprints stay visible	Drought stress	UF/IFAS LH025
Check leaves at the patch edge at dawn	Lesions, red threads, orange pustules or cottony growth	Foliar fungus	Purdue BP-124
Pull a plug and wash the roots	Short, dark, rotted roots under a patch that returns each year	Root disease (summer patch, necrotic ring spot, spring dead spot, take-all)	Purdue BP-115; UF/IFAS LH079

Grub thresholds by beetle species, and the dig method, are in our guide to grubs in lawns. For dog spots, Colorado State says pH-changing supplements and “female dogs only” claims do not hold up; the damage comes from nitrogen and salts, and heavier irrigation of the spot dilutes them (Colorado State Extension).

What weather triggers lawn fungus?

Lawn fungus is triggered by a measurable mix of temperature and hours of wet leaves, and each disease has its own window. Purdue’s seasonal profile puts gray snow mold at 31°F to 36°F under snow, dollar spot at 50°F to 70°F with long dew, and brown patch at dew periods of 12 hours or more averaging 65°F or warmer (Purdue BP-125).

Swipe the table sideways to see every column.

Disease	Temperature	Moisture or other trigger	When it shows	Source
Gray snow mold	31°F to 36°F under snow	Snow cover: mild after 40 to 60 days, moderate 60 to 90, severe over 90	Late winter, at snowmelt	Purdue BP-101; BP-125
Pink snow mold	32°F to 50°F	Cool, wet weather; snow not required	Late fall to mid-spring	Purdue BP-125
Red thread	45°F to 60°F	Leaf wetness over 12 hours	Mid to late spring, some fall	Purdue BP-125
Melting out	Cold, rainy weather	Rain; heavy spring nitrogen	April and May	Purdue BP-125
Dollar spot	50°F to 70°F (Purdue); 60°F to 75°F (UGA)	Dew over 8 hours	May to October; spring and fall in Georgia	Purdue BP-105; UGA C1091
Large patch	50°F to 70°F; patches appear as soil drops below 70°F	Long dew periods, wet or poorly drained soil	Fall and spring green-up	Purdue BP-125; FSA7527
Rust	50°F to 60°F	Evening dew over 10 hours on slow-growing turf	Late summer to mid-autumn	Purdue BP-110
Spring dead spot	Moist soil at 50°F to 70°F (infection in fall)	Cold winter after fall infection	Shows at spring green-up	Purdue BP-120
Necrotic ring spot	Soil 60°F to 75°F	Wet soil	Infects spring and fall; shows midsummer	Purdue BP-125
Brown patch	Nights above 60°F to 65°F; severe above 70°F lows and 90°F highs	Leaves wet 10 to 12 hours	Summer	NC State; Purdue BP-106
Summer patch	Soil at 3 in above 65°F for several days	Heat and drought later bring symptoms	Infects mid-May to June; shows from late July	Purdue BP-115
Pythium blight	Evenings averaging 68°F or more; days 86°F to 95°F	Dew over 14 hours; humidity above 90% for 14 hours	Hottest, wettest weeks of summer	Purdue BP-109; UMD
Gray leaf spot	70°F to 95°F	At least 14 hours of continuous leaf wetness	Mid to late summer, after tropical-storm rain	NC State; Purdue BP-107
Take-all root rot	Summer and early fall	Prolonged rainfall plus any turf stress	Roots infected 2 to 3 weeks before leaves show it	UF/IFAS LH079

1. Gray snow mold31
2. Pink snow mold32
3. Red thread45
4. Dollar spot50
5. Large patch50
6. Rust50
7. Spring dead spot (soil)50
8. Necrotic ring spot (soil)60
9. Brown patch65
10. Summer patch (3 in soil)65
11. Pythium blight68
12. Gray leaf spot70

Source: Purdue BP-125 (2013), BP-110, BP-120, BP-115; NC State Gray Leaf Spot in Turf Air temperature unless marked soil. Brown patch is Purdue's 65°F average during the wet period; NC State says it can start above 60°F at night. Pythium is the average evening temperature. Lower Midwest data except gray leaf spot (NC State).

Show the numbers

	Lower temperature threshold
Gray snow mold	31
Pink snow mold	32
Red thread	45
Dollar spot	50
Large patch	50
Rust	50
Spring dead spot (soil)	50
Necrotic ring spot (soil)	60
Brown patch	65
Summer patch (3 in soil)	65
Pythium blight	68
Gray leaf spot	70

The chart sorts the diseases by the lowest temperature at which each pathogen becomes active. Read it as a calendar: the left side is a fall-to-spring problem in the North, the right side a July and August problem. Brown patch, Pythium blight and gray leaf spot share the same night-time weather, and Purdue rates perennial ryegrass susceptible to all three, so one hot, humid week can start them together (Purdue BP-125; BP-124).

1. Dollar spot8
2. Brown patch10
3. Rust10
4. Red thread12
5. Pythium blight14
6. Gray leaf spot14

Source: Purdue BP-105, BP-106, BP-110, BP-125, BP-109; NC State Gray Leaf Spot in Turf Published as 'longer than' or 'at least' each figure. NC State gives 10 to 12 hours for brown patch; Purdue BP-125 gives 12 hours or more.

Show the numbers

	Minimum wet hours
Dollar spot	8
Brown patch	10
Rust	10
Red thread	12
Pythium blight	14
Gray leaf spot	14

Leaf wetness is the input you control. Every hour of irrigation that ends after sunset adds to the dew period, which is why NC State says watering after sunrise, in late afternoon or in the evening increases brown patch, and why UGA recommends knocking dew off with a hose for dollar spot (NC State; UGA C1091). Watering windows by grass are in our guide to the best time to water a lawn.

How do you treat lawn fungus?

You treat lawn fungus in eight steps: confirm the disease at the patch edge, rule out grubs and urine, change watering to before sunrise, move nitrogen in the direction that disease needs, raise the mower, bag clippings from active patches, spray only a product labeled for that disease and site, then reseed with a resistant grass. Purdue and UF/IFAS put cultural steps first (UF/IFAS PP154).

1. Sample the edge at dawn. Look at leaves from the margin of a patch with a 10x hand lens while dew is on. For gray leaf spot, seal a plug in a plastic bag overnight; gray mold on the leaves the next morning confirms it (Purdue BP-107).
2. Rule out grubs and urine. Dig 1 sq ft 2 to 3 inches deep and count; most turf tolerates up to 5 grubs per sq ft without visible damage (Purdue E-271). Do the plastic-bag ammonia test for urine (WSU).
3. Send a sample if the sign is unclear. Send a plug that spans healthy and sick grass to your state’s plant diagnostic lab or extension office; UF/IFAS says visual diagnosis alone is difficult and treatments differ completely by disease (UF/IFAS PP154).
4. Water before sunrise, deeply and less often. Skip late-afternoon and evening cycles; brown patch needs 10 to 12 hours of wet leaves and Pythium more than 14 (NC State; Purdue BP-109).
5. Adjust nitrogen for the disease you have. Add 0.2 lb N per 1,000 sq ft for red thread; hold summer nitrogen to 0.5 lb N per 1,000 sq ft or less during brown patch weather (Purdue BP-104; NC State). Rates by disease are in the next section.
6. Raise the mower and bag active patches. Purdue ties mowing below 2 inches to more leaf spot and melting out, and Arkansas says to bag clippings from large patch areas and avoid mowing wet turf (Purdue BP-103; FSA7527).
7. Spray only if patches keep spreading. Choose an active ingredient listed for that disease on a label that allows residential lawns, apply at the label rate, and water granules or root-disease sprays in as the label directs (UF/IFAS LH079).
8. Reseed with resistant grass. Purdue suggests Kentucky bluegrass to repair perennial ryegrass lost to gray leaf spot or Pythium blight, and names America, Majestic and Midnight among bluegrasses with moderate necrotic ring spot resistance (BP-107; BP-116).

Mowing during an outbreak spreads Pythium and large patch on wet blades, so mow those areas last and only when dry (Purdue BP-109; UMD); the evidence on dew and mowing for other diseases is in our article on mowing wet grass. Reseeding dates and rates are in our overseeding guide.

Does fertilizer make lawn fungus worse?

Fertilizer makes some lawn fungus worse and cures others, so the nitrogen move depends on the disease. Dollar spot, red thread and rust are worse on nitrogen-starved turf; brown patch, Pythium blight, large patch and spring dead spot are worse after heavy or badly timed nitrogen (UGA C1091; Purdue BP-120). Giving “no fertilizer” advice for all lawn fungus gets half the table wrong.

Disease	Made worse by	Nitrogen move	Source
Dollar spot	Low nitrogen	Light, frequent nitrogen; dollar spot often follows the late-spring N slump	UGA C1091; Purdue BP-105
Red thread	Low nitrogen	0.2 lb N per 1,000 sq ft in mid to late spring; fixed over 2 to 3 years of adequate N	Purdue BP-104
Rust	Low nitrogen, slow growth	0.2 to 0.5 lb N per 1,000 sq ft on chronic spots	Purdue BP-110
Fairy ring	Ring stimulates growth	Mask the dark band with 0.1 to 0.25 lb N per 1,000 sq ft around it	Purdue BP-113
Brown patch	Excess summer nitrogen	No more than 0.5 lb N per 1,000 sq ft per feeding in disease weather; 1 lb max at any one time	NC State; Purdue BP-106
Pythium blight	Lush growth, excess midsummer N	Avoid midsummer nitrogen near excessive levels	Purdue BP-109
Leaf spot and melting out	Heavy spring nitrogen	Put most of the year’s nitrogen in fall	Purdue BP-103
Large patch	Early-spring and late-season N	No N until May; max 2 lb N per 1,000 sq ft a season on zoysia, 4 lb on bermudagrass; stop after Aug. 15	Arkansas FSA7527
Spring dead spot	Late-summer nitrogen	Skip late-summer nitrogen on bermudagrass	Purdue BP-120
Take-all root rot	Nitrate N and uncoated urea	Slow-release N matched 1 to 1 with potassium; no lime	UF/IFAS LH079

The arithmetic is simple once the rate is set. A 5,000 sq ft lawn at 0.2 lb N per 1,000 sq ft needs 1 lb of actual nitrogen, which is about 2.2 lb of 46-0-0 urea (1 / 0.46). How to read fertilizer analysis and pick a product is covered in our lawn fertilizer guide, and yearly timing by grass in our lawn care schedule.

What is the best fungicide for lawn fungus?

The best fungicide for lawn fungus is one whose label lists your disease and allows residential lawns, because no product covers everything. Azoxystrobin (FRAC 11) is very effective on brown patch and large patch but does almost nothing for dollar spot, Purdue says; propiconazole (FRAC 3) and thiophanate-methyl (FRAC 1) cover dollar spot (Purdue BP-106; BP-105).

Homeowner lawn fungicides by active ingredient

Arkansas’s 2026 Plant Disease Control Products Guide is the only extension table we found that lists retail lawn products with their FRAC codes and rates. We matched each entry to its EPA registration and current label in October 2026; where the label and the guide differ, the label column wins, because the label is the legal rate. Product names identify registrations, not endorsements (UADA MP154, 2026).

Product as listed	Active ingredient	FRAC	Rate and limits	Lawn diseases listed (selected)	EPA registration
Scotts DiseaseEx Lawn Fungicide (granules)	azoxystrobin 0.31%	11	2 to 4 lb per 1,000 sq ft (label); every 14 to 28 days; max 37 lb per 1,000 sq ft a year	Brown patch, large patch, summer patch, gray leaf spot, snow molds, red thread, rust, Pythium, take-all, spring dead spot	EPA Reg. No. 538-330
BioAdvanced Fungus Control for Lawns (granules)	propiconazole 0.51%	3	2 lb preventive, 3.5 lb curative per 1,000 sq ft (label); curative every 14 days	Brown patch, dollar spot, red thread, rust, summer patch, snow mold	EPA Reg. No. 92564-38
Spectracide Immunox Fungus Plus Insect Control for Lawns (granules)	propiconazole 0.3% + lambda-cyhalothrin 0.02%	3	MP154: 4 lb per 1,000 sq ft. June 2026 label: not directly on residential lawns; spot treatments up to 2 sq ft	Brown patch, dollar spot, rust, leaf spot	EPA Reg. No. 9688-316
Ferti-lome Liquid Systemic Fungicide II	propiconazole 1.55%	3	5 fl oz in 1 gal water per 250 sq ft; brown patch every 14 days; max 8 applications a year (April 2026 label)	Brown patch, dollar spot, red thread, rust, take-all patch	EPA Reg. No. 53883-184-7401
Ferti-lome F-Stop Lawn and Garden (liquid)	myclobutanil 1%	3	5 1/3 fl oz in 1 gal water per 250 sq ft; 1 qt treats 1,500 sq ft; every 2 to 4 weeks	Brown patch, dollar spot, gray leaf spot, necrotic ring spot, red thread, rust, summer patch	EPA Reg. No. 7401-505
Bonide Infuse Systemic Disease Control Lawn and Landscape (granules)	thiophanate-methyl 2.08%	1	MP154: 7.5 lb per 5,000 sq ft. Label: max 3 lb per 1,000 sq ft per application, 12 lb a season, 14 days apart	Brown patch, dollar spot, gray leaf spot, necrotic ring spot, summer patch, take-all patch	EPA Reg. No. 53883-183-4
Scotts Lawn Fungus Control (granules)	thiophanate-methyl 2.3%	1	MP154: 6.75 lb per 2,400 sq ft	Large patch, gray leaf spot, snow molds, necrotic ring spot, red thread, take-all patch	EPA Reg. No. 538-88, listed inactive in EPA PPLS
Natural Guard Copper Soap Liquid Fungicide	copper octanoate 10%	M1	1.5 to 6 oz in 2.5 gal water per 1,000 sq ft	Dollar spot, rust, Ascochyta, Cercospora	EPA Reg. No. 67702-2-7401
H&I Agritech GreenCure	potassium bicarbonate	Not classified	1 to 2 tbsp per gal at first sign	Dollar spot, rust, powdery mildew, leaf spots	GreenCure registrations found in EPA PPLS are inactive

Two rows changed after the guide went to print. The label EPA accepted on June 10, 2026 for registration 9688-316, sold as Spectracide Immunox Fungus Plus Insect Control for Lawns granules, says “Do not apply directly to residential lawns” and limits spot treatments to 2 square feet, a restriction tied to its lambda-cyhalothrin insecticide (EPA label 9688-316). EPA’s database lists Scotts Lawn Fungus Control’s thiophanate-methyl registration, 538-88, as inactive, and the “Lawn Fungus Control” name now appears as an alternate brand of the azoxystrobin registration 538-330.

Which active ingredient works on which disease?

Extension trials rank active ingredients differently for each disease, and two of the most common lawn diseases need opposite picks. Arkansas rates flutolanil, metconazole, tebuconazole, triticonazole and triadimefon excellent on large patch, azoxystrobin and propiconazole good, and myclobutanil only fair (Arkansas FSA7527). Pythium blight needs its own chemistry entirely.

Disease	Active ingredients extension rates effective	FRAC	Timing or catch	Source
Brown patch	QoIs (azoxystrobin, pyraclostrobin) extremely effective; propiconazole and myclobutanil products also list it	11, 3	QoIs miss dollar spot: pair or rotate	Purdue BP-106; MP154
Dollar spot	Propiconazole, myclobutanil, tebuconazole; thiophanate-methyl; boscalid, fluxapyroxad	3, 1, 7	QoIs do not control it; few homeowner options (UGA)	Purdue BP-105; UGA
Large patch	Excellent: flutolanil, tebuconazole, triticonazole; good: azoxystrobin, propiconazole	7, 3, 11	First fall spray when 5-day 0 to 4 in soil average drops below 70°F	Arkansas FSA7527
Pythium blight	Mefenoxam, propamocarb, cyazofamid, fluopicolide; phosphonates preventive only	4, 28, 21, 43, P07	These do not control other diseases	Purdue BP-109
Summer patch	Penetrant products only; homeowner listings include azoxystrobin, propiconazole, myclobutanil, thiophanate-methyl	11, 3, 1	Start only after 3 in soil averages 65°F; 28-day intervals	Purdue BP-115; MP154
Necrotic ring spot	Thiophanate-methyl, propiconazole	1, 3	Spring sprays when 3 in soil averages 60°F to 70°F; water in	Purdue BP-116
Red thread	QoIs, flutolanil	11, 7	Before red threads form; nitrogen usually enough	Purdue BP-104
Rust	DMIs, QoIs	3, 11	Remedial only on established turf; first sign on new seedings	Purdue BP-110
Gray leaf spot	QoIs; thiophanate-methyl	11, 1	Resistant strains found in the Midwest	Purdue BP-107
Spring dead spot	DMI, QoI and SDHI combinations as soil drenches	3, 11, 7	1 or 2 fall sprays as 2 in soil nears 70°F	Purdue BP-120
Take-all root rot	Azoxystrobin, myclobutanil, propiconazole, pyraclostrobin, thiophanate-methyl	11, 3, 1	Start a month before usual symptoms, monthly, watered in	UF/IFAS LH079
Slime mold	None needed	None	Hose off or rake; gone in 1 to 2 weeks	Purdue BP-112

Granules or liquid is a delivery question. Foliar diseases such as dollar spot and brown patch need product on the leaves, so professional sprays go out in 2 to 5 gallons of water per 1,000 sq ft (NC State). Root diseases need the opposite: UF/IFAS says take-all sprays should be lightly watered into the root zone right after application, and Purdue suggests 2 to 4 gallons or 0.25 inch of irrigation for spring dead spot (UF/IFAS LH079; Purdue BP-120).

How much product does a 5,000 sq ft lawn need?

Label rates are written per 1,000 sq ft, per 250 sq ft or per bag area, which makes products hard to compare. The table converts each label rate to a 5,000 sq ft lawn: area divided by the rate’s area, times the amount per rate (EPA label 538-330; 53883-184).

Product	Label rate	Arithmetic for 5,000 sq ft	Amount for one application
Scotts DiseaseEx (538-330)	2 to 4 lb per 1,000 sq ft	5 x 2 lb to 5 x 4 lb	10 to 20 lb
BioAdvanced Fungus Control granules (92564-38)	2 lb preventive, 3.5 lb curative per 1,000 sq ft	5 x 2 lb; 5 x 3.5 lb	10 lb; 17.5 lb
Infuse Lawn and Landscape granules (53883-183-4)	Up to 3 lb per 1,000 sq ft per application	5 x 3 lb	Up to 15 lb
Ferti-lome Liquid Systemic Fungicide II (53883-184-7401)	5 fl oz in 1 gal per 250 sq ft	20 x 5 fl oz, in 20 gal water	100 fl oz
Ferti-lome F-Stop Lawn and Garden (7401-505)	1 qt (32 fl oz) per 1,500 sq ft	5,000 / 1,500 x 32 fl oz	107 fl oz
Season cap check: DiseaseEx	Max 37 lb per 1,000 sq ft a year	37 / 4 lb	9 curative applications at most

The 20 gallons of mix for a liquid product is what makes hose-end and pump-sprayer treatments of a whole lawn hard to do evenly, a point UF/IFAS makes when it lists measuring, diluting and applying as skills homeowners often lack (UF/IFAS PP154). Spot-treating only the patches and a 2 to 3 ft border cuts the amount sharply.

How do you rotate fungicides to prevent resistance?

You prevent fungicide resistance by never applying the same FRAC group twice in a row against the same disease and by mixing or alternating site-specific groups with a different group. Ohio State rates resistance concern high for thiophanate-methyl (FRAC 1), the DMIs (3), the strobilurins (11) and mefenoxam (4), and low for multi-site contacts such as chlorothalonil (M5) (Ohio State).

FRAC code	Class	Lawn active ingredients	Resistance concern (Ohio State)	Homeowner products in MP154
1	Benzimidazole	Thiophanate-methyl	High	Scotts Lawn Fungus Control; Bonide Infuse
3	DMI (sterol inhibitor)	Propiconazole, myclobutanil, tebuconazole, triticonazole, metconazole	High	BioAdvanced; Ferti-lome; Spectracide Immunox
11	QoI (strobilurin)	Azoxystrobin, pyraclostrobin, trifloxystrobin, fluoxastrobin	High	Scotts DiseaseEx
7	SDHI (carboxamide)	Flutolanil, boscalid, fluxapyroxad, penthiopyrad	Low to moderate	Professional only in MP154
4	Phenylamide	Mefenoxam	High	Professional only in MP154
2	Dicarboximide	Iprodione	Moderate to high	Professional only in MP154
M5	Chloronitrile	Chlorothalonil	Low	Professional turf; not for residential lawns (Purdue)
M1	Inorganic copper	Copper octanoate	Not rated (M codes are multi-site)	Natural Guard Copper Soap

A worked rotation for a tall fescue lawn with a brown patch history might run azoxystrobin (11) at the first nights above 65°F, then a propiconazole product (3) 14 to 28 days later, then back to 11 only if the weather holds. That alternation also covers dollar spot on the group 3 turn, which group 11 misses (Purdue BP-106). UGA gives the same rule for dollar spot: alternate fungicides from different chemical classes (UGA C1091).

Combination products already pair groups: Ohio State lists Headway as azoxystrobin plus propiconazole (11 + 3) and Concert as propiconazole plus chlorothalonil (3 + M5). A product containing 11 + 3 still counts as group 11 and group 3 for rotation, so the next application should be a different group, such as 1 (Ohio State).

When is a lawn fungicide not worth it?

A lawn fungicide is not worth it when the disease is cosmetic, the weather that drives it is ending, or the product cannot reach the target. Purdue calls red thread largely cosmetic, says slime molds need no treatment, and says summer patch sprays applied after symptoms appear have very limited effect (Purdue BP-104; BP-112; BP-115).

If your situation is	Do this	Why (source)
Brown patch on tall fescue while nights stay above 65°F	Water before sunrise, hold N to 0.5 lb per 1,000 sq ft or less, let cooler nights stop it; spray a labeled product only if patches keep expanding	Does not kill crowns or roots; turf regrows (Purdue BP-106)
Dollar spot in late spring or early summer	Feed light nitrogen; remove dew; use a group 3 or 1 product if needed	Worse on low N; QoIs do not control it (Purdue BP-105)
Red thread or rust	Add 0.2 to 0.5 lb N per 1,000 sq ft and keep mowing	Largely cosmetic; nitrogen outgrows it (BP-104; BP-110)
Greasy, collapsing patches in a hot, humid low spot on ryegrass	Stop evening watering, mow there last; reseed with Kentucky bluegrass or tall fescue if it recurs	Pythium kills plants within days (Purdue BP-109)
Zoysia or bermudagrass with patches that return each fall	Preventive fall fungicide when 0 to 4 in soil drops below 70°F; no N until May	Sprays after patches show are much less effective (FSA7527)
Kentucky bluegrass with frogeye rings in July	Core aerate in fall, mow at 3 in, water deeply; plan spring sprays only if it recurs	Summer patch sprays after symptoms barely work (Purdue BP-115)
Colored crust on grass after rain	Hose it off or rake it	Slime mold is not infectious (Purdue BP-112)
Dark green rings or arcs	Mask with 0.1 to 0.25 lb N per 1,000 sq ft	Fungicides must reach the soil; masking is cheaper (Purdue BP-113)
Product label lists chlorothalonil	Do not use it on a home lawn	Daconil SDG label: “Do not use on home lawns” (EPA 100-1694; Purdue BP-103)
Granules that also contain lambda-cyhalothrin	Read the bag for the residential-lawn restriction before you spread	June 2026 label for 9688-316 bars direct application to residential lawns (EPA label)

What several guides say vs what the extension source says

Several top-ranking lawn fungus pages give advice that the extension pathologists who study these diseases contradict. The most common error is treating “lawn fungus” as one problem with one fix. The table sets each claim beside the primary source, so you can see where a broad-spectrum spray or a blanket no-fertilizer rule would backfire (Purdue BP-106).

Claim on consumer guides	What the primary source says	Source
A broad-spectrum lawn fungicide treats most fungus	QoI products are extremely effective on brown patch but not on dollar spot; Pythium products control no other disease	Purdue BP-106; BP-109
Fertilizer feeds fungus, so stop fertilizing	Dollar spot, red thread and rust are worse on nitrogen-deficient turf	Purdue BP-105; BP-104
Apply fungicide as soon as you see the disease	Summer patch, large patch and take-all sprays work only before symptoms	Purdue BP-115; UF/IFAS LH079
Daconil (chlorothalonil) is a good lawn fungicide	The Daconil SDG label says do not use on home lawns, daycare or playground turf	EPA 100-1694; Purdue BP-103
Lawn fungus will not go away on its own	Brown patch, red thread and gray snow mold damage usually recovers once the weather changes	Purdue BP-106; BP-101

This page is general information, not pesticide advice. The label is the law: use only products registered for your state, labeled for residential turf and the disease you have, at the label rate. Some states require a license to apply fungicides for hire; see our guide to the pesticide applicator license for lawn care.

Question	Short answer	Best evidence
Main threat by grass?	Brown patch on tall fescue in summer; large patch on zoysia in fall and spring	Purdue BP-106; Arkansas FSA7527
Fastest killer?	Pythium blight: large areas in days	Purdue BP-109
Water when?	Before sunrise; never evening	NC State; UGA C1091
Feed or starve?	Feed for dollar spot, red thread, rust; hold N for brown patch, Pythium, large patch	Purdue; UGA; Arkansas
Homeowner fungicide groups?	FRAC 11, 3 and 1; rotate	UADA MP154 (2026)