GreenMaker Blog
Summer–Fall 2025 Lawn Fungi Guide: What’s Turning Your Grass Yellow (and What to Do About It)
We’ve got some fun-guys (and gals) working here at GreenMaker, but they’re not the ones turning your lawn yellow this summer and fall. In fact, our team is working hard to keep your grass lush, green, and healthy. The real culprits? A handful of fungi that thrive in hot days, humid nights, and heavy dew.
From patchy rings to mysterious straw-colored spots, lawn fungi are sneaky—and they don’t care how much time you’ve spent mowing or watering. The good news: once you know which fungus you’re dealing with, you can stop the spread and help your turf recover. Below you’ll find a simple symptom cheat sheet, disease spotlights, and the exact steps we take at GreenMaker to fix it fast.
Quick Symptom Cheat Sheet
- Yellow/tan spots the size of quarters → likely Dollar Spot.
- Large, irregular brown patches with dark borders → likely Brown Patch.
- Orange powder on shoes/mower → likely Rust.
- Dark, greasy-looking collapse after hot, humid nights → likely Pythium Blight.
- Perfect circles (rings) of fast-growing dark green or dead grass → likely Fairy Ring.
- Fading rings in Kentucky bluegrass mid/late summer → Necrotic Ring Spot/Summer Patch.
Tip: When in doubt, send us a clear photo in morning light. Close-ups + a few wider shots help us diagnose fast.
Top Lawn Diseases in Summer–Fall
Brown Patch (Rhizoctonia)
When it hits: Warm, humid stretches; night temps above ~65°F (18°C).
What you’ll see: Irregular, smoky-brown patches from dinner plates to kiddie-pool size; leaves may have “smoke rings.”
Why it happens: Excess nitrogen in summer, evening watering, dense/thatchy turf.
What helps: Morning-only irrigation, raise mowing height, reduce thatch, balanced (not heavy) nitrogen mid/late summer; consider a strobilurin or DMI fungicide rotation if severe.
Dollar Spot (Clarireedia)
When it hits: Late spring through fall in dew-heavy mornings.
What you’ll see: Bleached spots the size of a quarter to silver dollar; leaves with hourglass lesions; spots merge into larger blighted areas.
Why it happens: Nitrogen-starved turf, low mowing, leaf wetness.
What helps: Light, regular nitrogen (per your turf type), sharpen blades, water deeply & early, not daily; fungicide only if chronic.
Rust (Puccinia spp.)
When it hits: Late summer into fall, especially in slow-growing lawns.
What you’ll see: Orange dust on shoes/tires; thin, yellowing turf.
Why it happens: Low fertility and drought stress slow leaf growth.
What helps: Light nitrogen to spur new growth, consistent irrigation, keep blades sharp; usually no fungicide needed.
Pythium Blight
When it hits: Heat + high humidity, poorly drained or overwatered areas.
What you’ll see: Dark, greasy-looking, matted leaves; rapid spread along mower tracks.
Why it happens: Prolonged leaf wetness; nightly watering; heavy, soggy soils.
What helps: Improve drainage, water only at dawn, avoid fertilizing during heat waves; targeted fungicides if caught early.
Fairy Ring
When it hits: Anytime soils are dry with buried organic debris.
What you’ll see: Rings or arcs of darker green grass, mushrooms after rain, sometimes a band of dead turf.
Why it happens: Fungi decomposing organic matter and changing soil hydrophobicity.
What helps: Core aeration + wetting agents, deep watering, remove thatch. Severe rings may need localized soil replacement and professional treatment.
Summer Patch & Necrotic Ring Spot
When it hits: Mid/late summer; Kentucky bluegrass is susceptible.
What you’ll see: Fading circles or “frogeye” patterns—green center, dead ring.
Why it happens: Root-infecting fungi aggravated by compaction, heat, and shallow roots.
What helps: Core aeration, overseed with resistant cultivars (tall fescue mixes help), balanced fertility, appropriate mowing height; preventative fungicides may be warranted on repeat sites.
Look-Alikes to Rule Out
- Dog urine: small yellow spots with very green edges; often recur in favorite “zones.”
- Drought/heat stress: uniform bronzing on sunny slopes or along sidewalks.
- Grubs: turf peels up like carpet; wildlife/armadillo/skunk damage overnight.
- Weed killer burn: sharp edges that match spray patterns or footprints.
Our Proven Prevention Playbook
- Water like a pro: 1–1.5 inches per week total (including rain), applied at dawn 2–3 days per week. Avoid night watering.
- Mow high & often: Follow the 1/3 rule; raise height during heat (fescue 3–4", bluegrass/rye 2.5–3.5"). Keep blades sharp.
- Feed smart: Light, frequent nitrogen in summer for cool-season lawns only if needed; avoid heavy doses in heat.
- Thin the thatch: Core aeration annually if thatch > 0.5". Overseed with disease-resistant blends.
- Improve airflow: Prune dense shrubs/trees; increase morning sun where feasible.
- Rotate fungicides (if needed): Alternate FRAC groups to prevent resistance; spot-treat rather than blanket when possible.
DIY vs. Pro: When to Call GreenMaker
Light cases of rust or dollar spot often resolve with better watering and a small nutrition boost. Call us if you see any of the following:
- Rapid spread over days (especially in humidity).
- Perfect rings/arcs forming or mushrooms popping after rain.
- Recurring brown patch every summer despite “good” care.
- Pythium-like collapse after hot nights or along mower tracks.
We can confirm the diagnosis, apply targeted materials (the right actives, right rate, right timing), and tune your cultural plan so the problem doesn’t bounce back.
Late-Summer to Fall Care Calendar
| Timing | Do This | Why It Helps |
|---|---|---|
| Now–Early Fall | Morning irrigation; raise mowing height; spot nitrogen if pale; monitor dew-heavy areas. | Reduces leaf wetness window and stress that fuels disease. |
| Early–Mid Fall | Core aeration + overseeding (cool-season lawns). | Breaks compaction, cuts thatch, adds resistant cultivars. |
| Mid–Late Fall | Balanced fall fertilization; keep mowing until growth stops. | Builds roots and density for next year’s disease resistance. |
FAQ
Will fungicide “cure” my lawn overnight?
No. Fungicides stop new infection; existing leaf damage must grow out. Expect visible recovery as new blades replace damaged ones.
Are treatments safe for kids & pets?
We select labeled products and follow all re-entry intervals. Once dry (or as directed on the label), normal use can resume.
Is one treatment enough?
Some diseases need a short series of applications, timed 14–28 days apart, plus cultural adjustments (watering, mowing height, aeration).
Need a Hand?
Free Lawn Health Check: Send us photos or book a quick walk-through. We’ll ID the issue and give you a clear, step-by-step plan—DIY or full-service.
GreenMaker Notes
This guide covers the most common summer–fall turf diseases. Exact recommendations can vary by grass type (tall fescue, KBG, rye), soil, shade, irrigation, and local weather. Always follow product labels. If you’re unsure, we’re happy to confirm the diagnosis before you treat.
