Lawn Disease: Identification & Treatment Guide

A thick, green lawn can turn spotty and thin overnight when disease strikes. But identifying the problem early and treating it correctly can save your lawn.

This guide shows you how to recognize the most common lawn diseases and what to do about them.

Common Lawn Diseases and How to Identify Them

Dollar Spot

What it looks like:

• Small, circular tan/brown patches (size of a silver dollar, hence the name)
• Often start in spring/early summer
• Bleached appearance; grass blades have tan lesions

Conditions that trigger it:

• Cool, moist mornings
• Poor air circulation
• Under-fertilized lawns (low nitrogen)
• Thin grass

Treatment:

• Improve air circulation (thin canopy, reduce thatch)
• Increase nitrogen fertilization
• Fungicide if severe (apply early morning or evening)
• Water in morning only (avoid wet grass at night)

Brown Patch (Rhizoctonia)

What it looks like:

• Large, irregular brown patches (2–5 feet across)
• Often a dark ring at the patch edge
• Center may recover, leaving ring-shaped spot
• Worst in summer heat + humidity

Conditions that trigger it:

• Warm, humid nights (60–85°F)
• Excessive nitrogen
• Wet leaves at night
• Poor drainage

Treatment:

• Reduce nitrogen fertilization (especially in summer)
• Water early morning only
• Improve drainage if needed
• Reduce thatch
• Fungicide in summer if severe

Powdery Mildew

What it looks like:

• White/gray powder on grass blades (looks like baby powder)
• Often in shaded areas
• Blades may yellow
• Worse in cool, moist conditions

Conditions that trigger it:

• Shade (poor air circulation)
• Cool, moist spring/fall weather
• Humidity
• Dense turf

Treatment:

• Thin canopy (prune nearby plants, improve airflow)
• Avoid heavy shade areas (consider shade-tolerant grass)
• Water roots only, not foliage
• Reduce nitrogen (excess N promotes it)
• Fungicide if severe

Rust

What it looks like:

• Reddish-orange powder on grass blades
• Looks like rust on metal
• Blades may yellow
• Often on mower wheels (you'll see red stains)

Conditions that trigger it:

• Cool, moist conditions (spring/fall)
• Low nitrogen
• Dense thatch
• Shade

Treatment:

• Improve air circulation
• Increase nitrogen (apply light fertilizer)
• Reduce thatch (dethatch or aerate)
• Fungicide if severe
• Most rust clears on its own as temps change

Fairy Ring

What it looks like:

• Circular ring of darker, greener grass
• Dead/brown band inside or outside ring
• Mushrooms may appear around the ring
• Grass grows vigorously around edge

Conditions that trigger it:

• Buried organic matter (thatch, wood, old compost)
• Long-term fungal activity
• Poor drainage

Treatment:

• Aeration helps (relieves compaction)
• Deep watering (penetrates below fungal layer)
• Fungicide treatments are usually ineffective
• Improve drainage if possible
• Remove mushrooms (don't let them spread spores)
• May need to wait it out (can persist for years)

Slime Mold

What it looks like:

• Gray, tan, or black slimy coating on grass
• Looks alien (often spores on blade tips)
• Worst in humid, wet conditions
• More of a cosmetic issue than a disease

Conditions that trigger it:

• High humidity
• Wet grass
• Dense thatch

Treatment:

• It's harmless to grass
• Spray with water to remove
• Improve air circulation
• Don't fertilize heavily (promotes thick canopy)
• Will disappear on its own when conditions change

Prevention: The Best Medicine

Healthy Lawn = Disease Resistant

• Proper mowing: Cut at 2.5–3.5" (taller grass shades soil)
• Aeration: Relieves compaction; improves air circulation
• Balanced fertilization: Don't over-feed (excess N promotes disease)
• Thatch control: Over 0.5" blocks air and moisture
• Watering: Early morning only, 1–1.5" per week
• Good drainage: Fix wet areas
• Grass variety: Choose disease-resistant varieties

Treatment Steps

Step 1: Identify Correctly

• Look at patch size, color, shape, location
• Check blade lesions and stem damage
• Consider season and recent weather
• Compare to this guide or extension photos

Step 2: Environmental Adjustments

Most diseases respond well to:

• Reducing watering (morning only)
• Improving air circulation
• Reducing thatch
• Adjusting fertilization

These often clear the disease without fungicide.

Step 3: Fungicide (If Needed)

If environmental changes don't work after 2–3 weeks:

• Choose fungicide for the specific disease
• Apply early morning or evening (not during heat)
• Follow label instructions exactly
• May need 2–3 applications spaced 7–14 days apart
• Don't apply during extreme heat or drought

When to Call a Professional

Call a pro if:

• You can't identify the disease
• Multiple diseases are present
• Your lawn is severely affected (>25% of lawn)
• Environmental changes alone aren't working
• You want professional fungicide treatment

DIY is fine if:

• You can identify the disease
• It's isolated to small areas
• Environmental changes help
• You prefer not to use fungicides

FAQ: Lawn Disease

Q: Do all brown patches mean disease? A: No. Drought stress, urine burn, and compaction also cause brown spots. Disease typically has characteristic patterns (rings, lesions, etc.).

Q: Can I spread disease when mowing? A: Yes. Clean mower blades between lawns to avoid spreading. Mulching clippings is safe (don't bag and move to compost).

Q: Is fungicide safe for kids/pets? A: Most fungicides are safe once dry. Keep kids/pets off during application. Read label for safety info.

Q: Will disease go away on its own? A: Often, yes. Many diseases clear when conditions change (temperature, humidity, water). But treating early is faster.

Q: Should I worry about disease spreading to my neighbors? A: Some diseases spread via wind spores. Most stay localized. Good practices (reduce moisture, improve air) help minimize spread.

The Bottom Line: Stay Ahead

Lawn disease doesn't have to be scary. Identify early, adjust your practices, treat if needed, and most diseases clear quickly.

A thick, healthy lawn is your best defense against disease.

Last updated: March 2026