What’s the difference between pink and gray snow mold?

Gray snow mold (Typhula blight) needs long snow cover. Wisconsin Extension: about 60 days of continuous cover, and it typically does not develop if the ground freezes before the first snow. Pink snow mold (Microdochium patch) does not require snow — Cornell and Wisconsin say it can run in cool, wet weather from fall through spring. Pink patches often show a pink or reddish-brown margin and no sclerotia; gray patches often have a grayish halo and tiny BB-like sclerotia in the leaves. Cornell: a severe Microdochium infection can kill turf; Typhula blight is usually unsightly and rarely kills.

How big are the patches?

Wisconsin’s lawn-maintenance page: gray snow mold typically shows as circular tan or brown patches 1 to 3 feet across. Cornell: Typhula patches can reach several feet; Microdochium patches are usually less than a foot. Penn State: gray-mold patches range from a few inches to several feet and may coalesce. On short golf turf, Purdue describes gray-mold patches about 6 to 12 inches; on taller lawn turf the patches can be larger and less circular.

Should I cut the lawn extra short for winter?

Do not scalp. Keep mowing until the grass goes dormant so long blades do not mat. Wisconsin: mow at 2.5 to 3.5 inches right up to dormancy. Purdue gray-snow-mold profile: continue mowing to 2½ inches into the dormant period. UMN Turfgrass Science: on the last mow, consider lowering 0.5–1.0 inch to a final height of about 2.0–3.0 inches. Purdue’s pink-snow-mold profile: on Kentucky bluegrass and perennial ryegrass lawns, pink snow mold is most prevalent at 3 inches or greater. Height step-down, the one-third rule, and the Purdue-vs-UMN disagreement live on the last-fall-mow guide — this page only records what those sources tie to snow mold.

Does late nitrogen cause snow mold?

Extensions link lush, late nitrogen to worse disease. Wisconsin: nitrogen in late fall can enhance snow mold and should be avoided; do not apply fast-release sources such as urea or ammonium nitrate in fall. Penn State: use only moderate nitrogen in fall. MSU: fertility that produces lush growth just before snow-mold season makes turf more susceptible to Microdochium patch. Timing and yearly nitrogen rates belong on the fertilizing guide — do not stack an extra late feeding on top of that program to “green it up for winter.”

Should I pile driveway snow on the lawn with a snowblower?

Penn State and Purdue do not name snowblowers specifically. They do say not to create long-lasting snowbanks or piles on turf when you clear sidewalks and driveways, and not to accumulate snow in piles along drives and walks. Purdue documents gray-mold damage next to a sidewalk where piled snow sat more than 120 days. Wisconsin (Microdochium): a snow fence that limits accumulation, and faster melt, can reduce disease. Spread snow rather than building the same deep bank all winter. Machine prep is on the snow-blower-prep guide.

What do I do when the snow melts?

Stay off saturated turf. Lightly rake matted, crusted leaves so air can move (UMN, MSU, Purdue, Penn State, Wisconsin). Purdue: recovery is faster once the canopy is opened. Wisconsin: snow mold rarely kills turf; severe patches may need reseeding. UMN: the disease usually blights leaves, not the whole plant; fine fescue is less susceptible. Penn State: nitrogen after melt can speed recovery; a fungicide after symptoms appear is of no value. Do not dethatch a wet, injured lawn in early spring — thatch timing is on the dethatching guide.

Do I need a fungicide?

Purdue: fungicides are not recommended against gray or pink snow mold on home lawns. MSU: chemical control is generally not recommended on home lawns. Wisconsin: treatments are typically not warranted; they may be considered when a lawn has a history of Typhula blight and snow is expected to persist on unfrozen ground longer than three months, applied in October or November. Penn State: preventative sprays on high-value turf go on before first permanent snow (often late November in their region); spring sprays do not help. If a licensed applicator treats a high-value or repeatedly damaged lawn, follow the product label — this guide does not publish rates. Wisconsin names active ingredients labeled for these diseases; it does not replace the label.

Does thatch make it worse?

Wisconsin (Microdochium): remove thatch in September or May if the layer is greater than ½ inch. Penn State: Typhula sclerotia survive summer in leaf litter, thatch, and soil. How to measure thatch and when a vertical mower is justified is on the dethatching guide.

Snow mold: pink vs gray, last-mow height, and what to do at melt

The first bare spots after snowmelt are often not winterkill. They are two different fungi — one that needs a long snow blanket, and one that does not. Cooperative Extension is consistent on prevention (last mow, late nitrogen, snow piles) and on spring: rake the mat; do not spray after the fact.

Gray needs snow. Pink does not.

Wisconsin Extension: gray snow mold needs about 60 days of continuous snow cover, usually on unfrozen ground. Pink snow mold (Microdochium patch) runs in cool, wet weather — snow is optional. Cornell: Microdochium can kill turf; Typhula blight rarely does. Home lawns almost never need a fungicide (Purdue, MSU).

Two diseases, one spring mess

Left: pink snow mold can start without snow. Right: gray snow mold under long cover, with sclerotia. Bottom: last mow, skip late nitrogen, don’t bank snow, rake at melt.

Pink vs gray

Gray snow mold (Typhula blight) is caused by Typhula incarnata and T. ishikariensis (also spelled ishikariensis in some bulletins). Wisconsin: roughly circular bleached or straw patches up to two to three feet across, often matted and water-soaked, sometimes with a grayish-white mycelium at the edge. Tiny sclerotia give it away: T. incarnata reddish-brown, about 1/16 to 3/16 inch; T. ishikariensis black, about 1/64 to 1/16 inch, like pepper flakes. Penn State measures those bodies at 0.5 to 2.5 mm and describes the mat as papier-mâché. Wisconsin: T. incarnata is more common in the southern half of the state and usually spares the crown; T. ishikariensis (north) can kill crowns, so recovery is slower.

Gray mold’s weather is specific. Wisconsin: more than 60 days of snow on unfrozen ground with soil about 30 to 40°F; it typically does not develop if the ground freezes before the first snow, or if a midwinter thaw exposes turf to colder air. Purdue’s golf-turf rule of thumb: mild symptoms after 40 to 60 days of cover, moderate after 60 to 90 days, severe when cover exceeds 90 days. On taller-mown turf, Purdue says some less conspicuous symptoms may appear after 40 days.

Pink snow mold (Microdochium patch, formerly Fusarium patch) is Microdochium nivale (some older Purdue sheets say M. nivale). It does not need snow. Wisconsin: more severe at 30 to 60°F, wet weather, alkaline soils, and high nitrogen early or extremely late in the season. MSU: the fungus grows on residue below 60°F; cool, wet spells at 32–46°F with freeze/thaw, fog, or drizzle are especially favorable. Cornell: patches usually less than a foot, with a pinkish margin when wet, and no sclerotia. MSU: on lawn-height turf the color is often a smokier brown than the tan-and-pink rings on golf greens; dog urine spots lack those rings and the fluffy mycelium.

Host notes, not a ranking of your seed bag: Wisconsin — all cool-season lawn grasses can get snow mold; some hard fescues show more resistance; tall fescue and perennial ryegrass are generally more susceptible than fine fescues and Kentucky bluegrass. UMN: all Minnesota lawn grasses can be affected; fine fescue is less susceptible. Cornell: bentgrasses are most susceptible. Purdue pink mold: most damaging on creeping bentgrass and annual bluegrass on golf turf; on Kentucky bluegrass and perennial ryegrass lawns it is most prevalent at 3 inches or greater.

Prevention — without rewriting the last-mow or fertilizer guides

Last mow. Long grass that lodges under snow is the microenvironment these fungi like. Wisconsin: mow at 2.5 to 3.5 inches until winter dormancy so the canopy does not lay over. Purdue gray mold: 2½ inches into dormancy. UMN: drop the last cut 0.5–1.0 inch to about 2.0–3.0 inches. Those numbers do not all match — the last-fall-mow guide is where we walk through MSU, Purdue, UMN, and Ohio State without flattening them into one invented height. This page’s job is the disease link: keep cutting until growth stops, and do not leave a tall, unmown mat.

Late nitrogen. Wisconsin: skip late-fall nitrogen and do not put fast-release urea or ammonium nitrate on in the fall. Penn State: only moderate nitrogen in fall. MSU: don’t force lush growth into the snow-mold window; time feeding so turf can harden off. Rates, holidays, and slow-release fractions stay on the fertilizing guide.

Thatch and leaves. Wisconsin (Microdochium): dethatch in September or May if thatch is greater than ½ inch. Purdue: rake to remove leaf piles. UMN: mulch or remove excessive leaf litter. How to measure thatch — and when a power rake is justified — is on the dethatching guide.

Snow piles. Gray mold is worst where snow is deepest and lasts longest (Penn State: along drives and walks, or over a hill brink). Cultural rule from Penn State: when you remove snow from sidewalks and driveways, do not create long-lasting snowbanks on turf. Purdue home-lawn help: avoid accumulating snow in piles along driveways and sidewalks; their disease profile shows damage beside a walk where piled snow lasted more than 120 days. They do not single out snowblowers. The practical reading: don’t throw every pass onto the same lawn strip all winter. Snow-blower prep is the machine checklist, not a disease bulletin.

Wisconsin also mentions a snow fence to limit Microdochium accumulation and encouraging faster melt. Soil pH at or below 7.0 is on their Microdochium sheet for new and established lawns.

What to do at melt

Wait until the surface can take a footprint without smearing. Then lightly rake to break the crust and stand the blades up (UMN, MSU, Purdue, Penn State, Wisconsin).
Do not expect a spring fungicide to erase what already happened. Penn State: applying fungicides after gray snow mold symptoms appear is of no value.
Wisconsin: damage rarely kills turf; rake to promote recovery; reseed severe patches. UMN: leaves are blighted more often than whole plants. Wisconsin on T. ishikariensis: crown death is possible — those spots may not fill without seed.
Penn State and MSU: a spring nitrogen feeding can help the lawn grow out of foliar blight. Use the fertilizing guide — not a mystery “snow-mold rate.”

Fungicides — home lawn vs high-value turf

Purdue’s gray and pink profiles: fungicides are not recommended for home lawns. MSU: generally not recommended on home lawns. Wisconsin: usually not cost-effective; consider a preventative only with a disease history and a forecast of snow on unfrozen ground longer than three months, applied in October or November (Typhula) or October or November (Microdochium). Penn State: on high-value turf, sprays go on before first permanent snow, often late November in their geography; combinations of different active ingredients are often used there.

Wisconsin lists labeled active ingredients (for example azoxystrobin, propiconazole, pyraclostrobin, and tebuconazole for Typhula; a longer Microdochium list including chlorothalonil, iprodione, and PCNB among others). MSU notes chlorothalonil and mancozeb as contacts used on golf turf without lasting snow, on a two- to four-week interval in that setting, and systemics where snow lasts three or more months. This page does not publish product rates, tank mixes, or a homeowner spray calendar. If a professional treats a repeatedly wrecked lawn, they follow the current label — or you hire them to do that. Spring “rescue” sprays are not a substitute for raking.

FAQ

What’s the difference between pink and gray snow mold?: Gray snow mold (Typhula blight) needs long snow cover. Wisconsin Extension: about 60 days of continuous cover, and it typically does not develop if the ground freezes before the first snow. Pink snow mold (Microdochium patch) does not require snow — Cornell and Wisconsin say it can run in cool, wet weather from fall through spring. Pink patches often show a pink or reddish-brown margin and no sclerotia; gray patches often have a grayish halo and tiny BB-like sclerotia in the leaves. Cornell: a severe Microdochium infection can kill turf; Typhula blight is usually unsightly and rarely kills.
How big are the patches?: Wisconsin’s lawn-maintenance page: gray snow mold typically shows as circular tan or brown patches 1 to 3 feet across. Cornell: Typhula patches can reach several feet; Microdochium patches are usually less than a foot. Penn State: gray-mold patches range from a few inches to several feet and may coalesce. On short golf turf, Purdue describes gray-mold patches about 6 to 12 inches; on taller lawn turf the patches can be larger and less circular.
Should I cut the lawn extra short for winter?: Do not scalp. Keep mowing until the grass goes dormant so long blades do not mat. Wisconsin: mow at 2.5 to 3.5 inches right up to dormancy. Purdue gray-snow-mold profile: continue mowing to 2½ inches into the dormant period. UMN Turfgrass Science: on the last mow, consider lowering 0.5–1.0 inch to a final height of about 2.0–3.0 inches. Purdue’s pink-snow-mold profile: on Kentucky bluegrass and perennial ryegrass lawns, pink snow mold is most prevalent at 3 inches or greater. Height step-down, the one-third rule, and the Purdue-vs-UMN disagreement live on the last-fall-mow guide — this page only records what those sources tie to snow mold.
Does late nitrogen cause snow mold?: Extensions link lush, late nitrogen to worse disease. Wisconsin: nitrogen in late fall can enhance snow mold and should be avoided; do not apply fast-release sources such as urea or ammonium nitrate in fall. Penn State: use only moderate nitrogen in fall. MSU: fertility that produces lush growth just before snow-mold season makes turf more susceptible to Microdochium patch. Timing and yearly nitrogen rates belong on the fertilizing guide — do not stack an extra late feeding on top of that program to “green it up for winter.”
Should I pile driveway snow on the lawn with a snowblower?: Penn State and Purdue do not name snowblowers specifically. They do say not to create long-lasting snowbanks or piles on turf when you clear sidewalks and driveways, and not to accumulate snow in piles along drives and walks. Purdue documents gray-mold damage next to a sidewalk where piled snow sat more than 120 days. Wisconsin (Microdochium): a snow fence that limits accumulation, and faster melt, can reduce disease. Spread snow rather than building the same deep bank all winter. Machine prep is on the snow-blower-prep guide.
What do I do when the snow melts?: Stay off saturated turf. Lightly rake matted, crusted leaves so air can move (UMN, MSU, Purdue, Penn State, Wisconsin). Purdue: recovery is faster once the canopy is opened. Wisconsin: snow mold rarely kills turf; severe patches may need reseeding. UMN: the disease usually blights leaves, not the whole plant; fine fescue is less susceptible. Penn State: nitrogen after melt can speed recovery; a fungicide after symptoms appear is of no value. Do not dethatch a wet, injured lawn in early spring — thatch timing is on the dethatching guide.
Do I need a fungicide?: Purdue: fungicides are not recommended against gray or pink snow mold on home lawns. MSU: chemical control is generally not recommended on home lawns. Wisconsin: treatments are typically not warranted; they may be considered when a lawn has a history of Typhula blight and snow is expected to persist on unfrozen ground longer than three months, applied in October or November. Penn State: preventative sprays on high-value turf go on before first permanent snow (often late November in their region); spring sprays do not help. If a licensed applicator treats a high-value or repeatedly damaged lawn, follow the product label — this guide does not publish rates. Wisconsin names active ingredients labeled for these diseases; it does not replace the label.
Does thatch make it worse?: Wisconsin (Microdochium): remove thatch in September or May if the layer is greater than ½ inch. Penn State: Typhula sclerotia survive summer in leaf litter, thatch, and soil. How to measure thatch and when a vertical mower is justified is on the dethatching guide.

Last fall mow — canopy height into winter, including the universities that disagree on the last notch.
Fertilizing — when nitrogen belongs on a cool-season lawn, without a late soluble dump.
Dethatching — the ½-inch thatch check Wisconsin ties to Microdochium.
Mower winterization — put the mower away after the last cut.
Snow blower prep — fuel and chute safety; pile snow with the Penn State / Purdue bank rule in mind.
November checklist — last mow and snow gear on the same calendar.

Sources

Wisconsin Horticulture — Typhula blight (gray snow mold): >60 days snow on unfrozen ground; 30–40°F; sclerotia sizes; crown vs leaf; Oct/Nov fungicides; >3 months snow for home-lawn consideration.
Wisconsin Horticulture — Microdochium patch: no-snow disease; 30–60°F; pH ≤ 7.0; thatch > ½ inch in Sept or May; no fast-release N in fall; snow fence.
Wisconsin Horticulture — Lawn maintenance: gray mold ~60 days cover; patches 1–3 ft; mow 2.5–3.5 in to dormancy; skip late-fall N.
UMN Turfgrass Science — November 2023 home lawn newsletter: last mow drop 0.5–1.0 in to about 2.0–3.0 in; leaf litter.
UMN Extension — What does winter injury look like on your lawn?: patches up to 3 ft; three pathogens; fine fescue less susceptible; light raking.
Cornell Cooperative Extension (Monroe) — Snow molds of turfgrass: Typhula vs Microdochium; patch size; kill vs rarely kill; bentgrass.
Penn State Extension — Gray snow mold: snowbanks from walks and drives; moderate fall N; rake + N at melt; spring fungicide of no value; sclerotia 0.5–2.5 mm.
MSU Extension — Microdochium patch: not generally for home lawns; 32–46°F wet weather; <60°F survival; 3+ months snow and systemics on golf turf.
MSU Extension — Winter damage: molds, moles and voles: light raking; spring fertilizer for recovery.
Purdue Extension BP-101-W — Gray snow mold: 2½-in last mow; 40/60/90-day golf rule of thumb; >120-day sidewalk pile; no home-lawn fungicide.
Purdue Extension BP-102-W — Pink snow mold: most prevalent on KBG and rye lawns at 3 in or greater; no home-lawn fungicide; don’t pile snow on the same side of drives and walks.