Keast Lawn & Snow • July 2026 • East Lansing, MI

Short Answer: Three fungal diseases drive most of the disease damage we see on mid-Michigan lawns from mid July through August. Brown patch produces large circular patches (two to three feet across) with a darker ring on the outside, mostly on tall fescue and ryegrass, when night temperatures stay above 65 degrees and humidity is high. Pythium blight is the fastest-moving and most destructive of the three, presenting as orange-tinted greasy streaks that follow water flow patterns and can wipe out entire sections of lawn in under 48 hours under the worst conditions. Dollar spot leaves small bleached patches the size of a silver dollar to a softball, often running together into larger irregular areas, common on Kentucky bluegrass and ryegrass during warm humid weather. Each one has a different field signature, a different cultural response, and a different fungicide class that actually works. Spraying wrong is wasted money. ID first.

Mid-Michigan has a roughly six week window from early July through mid August when fungal disease pressure on cool-season lawns is at its highest. Warm humid days, warm humid nights, and active grass tissue all combine to create the conditions that these three pathogens need. Properties with irrigation are more vulnerable than properties without (because the irrigation creates the consistent moisture the disease wants). Properties with poor air circulation, heavy thatch, and recent nitrogen applications are more vulnerable than properties without those issues. And once disease is active, the right response depends entirely on which disease you are looking at.

This is a field guide to the three we see most often on East Lansing area lawns. We will walk through how to identify each one, what conditions favor it, what cultural changes help, and what we actually spray when the situation calls for it. The goal is not to turn every homeowner into an amateur turf pathologist. The goal is for you to know enough to recognize when you are looking at disease versus heat damage, and to ask the right questions when someone shows up with a sprayer.

Brown Patch

Brown patch is caused by the fungus Rhizoctonia solani. It is the most common warm-season disease on mid-Michigan lawns where tall fescue or perennial ryegrass make up a significant portion of the turf. Kentucky bluegrass is less susceptible but not immune, particularly in newer bluegrass stands that are still building up the lignin and other structural defenses that mature bluegrass develops.

What it looks like. Brown patch produces roughly circular patches, typically one to three feet in diameter, with a tan or light brown interior and a thin darker ring (often called a smoke ring) on the leading edge of the patch. On dewy mornings, especially when temperatures are still warm at sunrise, you can sometimes see grayish white mycelium webbing across the affected grass blades. The patches often start in shaded areas with poor air circulation and spread outward. Multiple patches in the same area may join together into larger irregular shapes.

Conditions that favor it. Night temperatures above 65 degrees for three or more consecutive nights. Daytime temperatures in the 80s. High humidity (70 percent or higher relative humidity overnight). Extended leaf wetness, especially when evening watering or late afternoon storms keep the canopy wet through the night. Excess nitrogen pushes susceptibility hard because soft fast-growing tissue is the perfect host.

Cultural response. Mow at four inches or so to improve air movement at the canopy level. Water in early morning only (so leaves dry by midday). Skip any nitrogen applications during the active window. Reduce thatch with raking or hand removal if it is over half an inch. Improve drainage and air circulation in low spots if you have ongoing issues.

Fungicide response. When the cultural changes are not keeping up and active spread is visible, we use either azoxystrobin (Heritage) or a chlorothalonil-based product on properties where strobilurin resistance is a concern. Both work well on brown patch when applied at label rate with adequate water carrier (two to three gallons per thousand square feet). One application during the active window is often enough on a residential lawn. Heavy infestations on susceptible cultivars sometimes need a follow-up two to three weeks later.

Pythium Blight

Pythium is the disease nobody wants to find on their lawn. It is caused by various Pythium species (P. aphanidermatum is the most common on cool-season turf in our climate) and it moves faster than any other disease in our area. A lawn that looks fine on Monday morning can have visible pythium damage by Monday evening and be substantially destroyed by Wednesday. The window between first symptoms and major loss is sometimes 48 hours or less.

What it looks like. Small (one to six inch) patches that start with a greasy water-soaked appearance, often with an orange or red tint to the affected blades. Patches frequently run together into streaks that follow water flow patterns (the disease spreads through water movement across the lawn surface). On dewy mornings, look for a grayish slimy film across affected areas, sometimes called cottony blight when the mycelium is thick. The smell of an active pythium outbreak is often faintly off, almost sour, which is something the other two diseases do not produce.

Conditions that favor it. Hot humid weather with night temperatures above 68 degrees. Saturated soils after heavy rain or excessive irrigation. Areas with poor drainage. Heavy thatch. The combination of heat plus standing water on the lawn surface is essentially perfect pythium weather. We see most of our pythium calls during the third week of July through mid August in years with significant summer storms.

Cultural response. Pythium responds less reliably to cultural changes than the other two diseases because once it is active, it spreads faster than cultural shifts can take effect. The big preventive items are not overwatering, not mowing wet lawns (the mower tracks spread the disease aggressively), and not applying high nitrogen during the active window. Improving drainage on low spots is the biggest long-term protection.

Fungicide response. Pythium does not respond to the same products that handle brown patch and dollar spot. The active ingredients that work are mefenoxam (Subdue), propamocarb (Banol), or phosphonate-based products. These need to land before significant damage has occurred or in the very early stages of an outbreak. By the time pythium has covered 20 percent of a lawn, even the right fungicide is mostly a holding action. The damaged turf will need to be reseeded in September.

Dollar Spot

Dollar spot is caused by Clarireedia species (formerly classified as Sclerotinia homoeocarpa). It is probably the most common cool-season disease on East Lansing area lawns through July and August, and it is the one we encounter on the widest range of properties because it tolerates lower nitrogen, drier conditions, and broader temperature ranges than brown patch or pythium.

What it looks like. Small bleached or tan patches roughly the size of a silver dollar (one to three inches) early in the disease cycle. As the disease progresses, patches enlarge and run together into larger irregular dead areas. The individual blades within a patch show hourglass-shaped lesions when looked at closely: a bleached band across the middle of the blade with a darker tan band above and below. On dewy mornings, fine white mycelium tufts may be visible across affected blades. The mycelium is finer and less obvious than brown patch and disappears quickly as the morning warms.

Conditions that favor it. Warm days (70 to 85 degrees), warm humid nights, extended leaf wetness, and low nitrogen status. Dollar spot is unusual in that it gets worse when the lawn is underfertilized rather than overfertilized. Lawns that have been intentionally kept on a light fertility program (organic-based programs, neglected lawns, properties pushing through summer dormancy without any nutrition) often show dollar spot first.

Cultural response. Light nitrogen applications can actually suppress dollar spot, which is the opposite of the brown patch response. Bumping the fertility on a lawn with active dollar spot by a quarter to half pound of nitrogen per thousand square feet often slows the spread. Mow at three and a half to four inches, water in the morning only, and remove dew when feasible (some homeowners drag a long pole or a wet rope across the lawn at sunrise to knock the dew off, which sounds extreme but works).

Fungicide response. Propiconazole (Banner Maxx), myclobutanil (Eagle), or chlorothalonil all work well on dollar spot. We tend to rotate active ingredients across applications to manage resistance, which has been an increasing problem with dollar spot specifically over the last decade. One properly timed application usually handles a residential outbreak. Heavy infestations may need a second three to four weeks later.

Telling Them Apart at a Glance

Three quick patterns to remember. Brown patch produces larger patches (one to three feet) with darker rings, mostly on tall fescue and ryegrass, under hot humid conditions. Pythium produces small fast-moving streaks with orange tint and a slimy film, often following water flow patterns, under hot wet conditions. Dollar spot produces small bleached patches with hourglass-shaped lesions on individual blades, across a wide range of grass species, often on lower-fertility lawns.

If you are uncertain, pull a small sample of affected and adjacent grass and look at the individual blades under good light. The hourglass lesions of dollar spot are diagnostic. The smoke-ring edge and large patch size of brown patch are diagnostic. The greasy orange streaking of pythium is diagnostic. Heat damage and drought damage produce none of those signatures because they are not disease.

What We Do on a Disease Call

When we get a call about brown patches in July or August, we walk the property and look for the field signatures above. We sometimes take a small turf sample back to the lab if the ID is borderline. We check the irrigation timing and coverage because mistimed irrigation is the most common contributor to all three diseases. We look at the fertility history because high nitrogen feeds brown patch and low nitrogen feeds dollar spot. We assess the soil drainage on the affected areas because pythium especially is driven by saturation.

Then we make a decision about whether the response is cultural, chemical, or both. On many residential properties, simple changes to irrigation timing and a one-time fungicide application handle the immediate outbreak. On lawns with chronic issues, we often plan a longer-term shift in mowing height, fertility, irrigation, and species composition (some grass cultivars are dramatically more disease-resistant than others, which becomes relevant during fall renovation planning).

What to Do Next

If you are seeing patches that look like any of the three diseases above and want a confirmed ID and a treatment plan, we are glad to walk the property. The right diagnosis in mid-July saves both the immediate damage and the cost of spraying the wrong product. We serve East Lansing, Lansing, Okemos, Haslett, Williamston, Holt, DeWitt, and surrounding mid-Michigan communities.

Call us at 517-894-5792 or visit keastlawn.com to schedule a disease assessment.