The fastest way to tell the difference is by looking at the lesion pattern on the grass blade and the size of the affected area. Brown patch typically creates large, circular patterns up to 3 feet wide, while dollar spot produces small, silver-dollar-sized circles rarely exceeding 6 inches.
Identifying Brown Patch (Rhizoctonia solani)
Brown patch is a fungal nightmare for warm-season grasses like St. Augustine and Zoysia in the South, but it also hits Tall Fescue in the transition zone.
Look for these specific signs:
- The “Smoke Ring”: A dark, grayish-black outer rim visible in the early morning when the grass is wet.
- Large Circles: Patches that range from 6 inches to over 3 feet in diameter.
- Easy Pull: Affected grass blades pull away easily from the stolon because the base of the leaf sheath has rotted.
- Leaf Lesions: Tan lesions with dark brown borders that don’t necessarily span the entire width of the blade.
Identifying Dollar Spot (Clarireedia jacksonii)
Dollar spot thrives on cool-season grasses like Kentucky Bluegrass and Bentgrass, but it is notorious for attacking lawns with low nitrogen levels.
Key identifiers include:
- Size: Small, sunken, straw-colored spots roughly the size of a silver dollar.
- The Hourglass Lesion: This is the “smoking gun.” Lesions on the leaf blade are bleached white and shaped like an hourglass, cinched in the middle.
- Mycelium: In heavy dew, you will see white, cobweb-like growths (mycelium) covering the spots.
- Widespread Pitting: While spots start small, they can coalesce into large, irregular bleached areas if left untreated.
Root Causes: Why Is Your Yard Dying?
Understanding the environmental triggers is crucial for choosing the right treatment strategy. Both fungi thrive in humidity, but their temperature preferences differ.
Causes of Brown Patch
- High Temperature/Humidity: It peaks when night temperatures stay above 65°F and day temperatures hit 80°F or higher.
- Excess Nitrogen: Over-fertilizing with fast-release nitrogen during hot, humid spells is like pouring gasoline on a fire.
- Evening Watering: Leaving the turf canopy wet for more than 10 hours overnight.
Causes of Dollar Spot
- Nitrogen Deficiency: Unlike brown patch, dollar spot loves “hungry” lawns. If you haven’t fertilized, your lawn is at risk.
- Drought Stress: Lawns that are kept too dry or have deep thatch layers (over 0.5 inches) are susceptible.
- Extended Leaf Wetness: Heavy dew or frequent light irrigation that doesn’t reach the roots.
Step-by-Step Treatment and Solutions
Once you have identified the culprit, you must act fast to prevent the fungi from reaching the root crown and killing the plant entirely.
Phase 1: Chemical Intervention
For immediate knockdown, you need professional-grade fungicides.
- For Brown Patch: Use products containing Azoxystrobin. Scotts DiseaseEx is a top-tier consumer choice. For liquid applications, Heritage G or Spectracide Immunox works effectively.
- For Dollar Spot: Look for Propiconazole or Thiophanate-methyl. Ortho Disease B Gon or BioAdvanced Fungus Control are highly effective against the hourglass lesions.
Dosing Tip: Apply granular treatments at a rate of 2 lbs to 4 lbs per 1,000 sq ft depending on the severity of the infection. Always water in granular fungicides with approximately 0.25 inches of water to activate the active ingredients.
Phase 2: Cultural Adjustments
You cannot spray your way out of a bad maintenance routine.
- Adjust Irrigation: Water only between 4:00 AM and 8:00 AM. This allows the sun to dry the leaf blades quickly.
- Mowing Height: Raise your mower blade. For Fescue, stay at 3.5 to 4 inches. For St. Augustine, keep it at 3 to 4 inches.
- Aeration: If your soil is compacted, perform core aeration in the fall to improve drainage and air circulation.
Comparison: Symptoms vs. Common Confusions
It is easy to mistake fungal disease for other issues like pest damage or chemical burns. Use this table to differentiate.
| Feature | Brown Patch | Dollar Spot | Grubs / Chinch Bugs |
| Spot Size | 6″ to 36″ | 1″ to 6″ | Irregular patches |
| Key Sign | Dark “smoke ring” border | Hourglass leaf lesion | Grass peels up like carpet |
| Fertilizer Effect | Nitrogen makes it worse | Nitrogen helps it heal | No effect |
| Primary Grass | St. Augustine, Zoysia, Fescue | Bluegrass, Ryegrass, Bentgrass | All types |
To wrap up your lawn recovery plan, remember that healthy soil is the best defense against fungal outbreaks. If you struggle with persistent Brown Patch or Dollar Spot, your soil might be too compacted for proper drainage and airflow. Learn how to open up your turf and strengthen root systems by checking out our expert guide on When Should You Aerate Your Lawn? to ensure your next treatment delivers maximum results.
People Also Ask
Can I mow my lawn if I have brown patch or dollar spot?
Yes, but you must be extremely careful not to spread the fungal spores to healthy sections of your yard. Always mow the diseased areas last, and wash the underside of your mower deck with a bleach-water solution afterward. Bag your clippings instead of mulching them to remove the infected plant tissue from the lawn.
How long does it take for the grass to recover after treatment?
Fungicides are “preventatives” or “curatives” that stop the fungus, but they do not instantly regrow the grass. After applying a product like Scotts DiseaseEx, the fungus should stop spreading within 48 to 72 hours. However, visible recovery of the brown areas may take 3 to 6 weeks during the active growing season.
Is dollar spot dangerous to pets or humans?
The fungus itself is generally not harmful to humans or pets; however, the chemical treatments used to kill it require caution. After applying liquid or granular fungicides, keep pets and children off the yard until the product has been watered in and the grass is completely dry to prevent skin irritation or accidental ingestion.