Dollar Spot vs Brown Patch: How to Tell Them Apart

Dollar spot and brown patch are the two most common fungal lawn diseases in the United States, and they're frequently confused with each other — and with each other's treatments. Applying a product aimed at brown patch to a dollar spot infection wastes money and time while the disease continues spreading. Getting this identification right is worth 5 minutes of investigation.

The key visual differences

Patch size is the most important distinguishing factor. Dollar spot patches are roughly the size of a silver dollar — 2 to 6 inches in diameter. If you have a lawn full of small, distinct dead circles, you almost certainly have dollar spot. According to NC State TurfFiles, brown patch patches are much larger, typically 6 inches to 3 feet in diameter (sometimes larger), and tend to run together as the infection progresses.

Look at individual grass blades. Dollar spot creates distinctive lesions with a bleached center and reddish-brown border that wraps across the full width of the blade — the lesion looks like it was tied with a band. In the early morning when dew is present, you may also see white, cottony mycelium (fungal threads) spanning the grass between infected blades. Brown patch creates different blade lesions: tan centers with dark brown margins, and the infected tissue tends to die from the tip downward.

The smoke ring. Brown patch typically produces a darker "smoke ring" border — a ring of water-soaked, grayish grass at the outer edge of the patch visible in the morning. Dollar spot doesn't produce this ring; its patches have less distinct, irregular edges.

What causes each

Dollar spot thrives in conditions that are almost the opposite of brown patch: it prefers cool nights and warm days (the transition seasons, not peak summer), morning dew, and — critically — nitrogen-deficient lawns. This is why dollar spot often signals that your lawn needs fertilizing, not fungicide. As University of Minnesota Extension notes, underfed, slow-growing grass is highly susceptible; a well-fed lawn with active growth is relatively resistant.

Brown patch, in contrast, is driven by warm nights (above 70°F) and excess nitrogen. Heavily fertilized lawns with lush summer growth are the most susceptible. Evening watering that keeps foliage wet overnight is the primary human trigger. NC State TurfFiles on brown patch identifies extended leaf wetness periods — greater than 10 hours — combined with air temperatures above 70°F at night as the core environmental trigger.

This creates an almost paradoxical situation: the treatment for dollar spot (apply nitrogen) is a risk factor for brown patch. Getting the identification right determines the correct course of action.

Treatment

For dollar spot: Start by applying a light nitrogen fertilizer to encourage growth — I typically recommend 0.5 lbs of actual nitrogen per 1,000 sq ft as a starting point. In many cases this alone resolves minor infections by allowing the lawn to outgrow the disease. Improve irrigation timing (switch to morning watering). If the infection is severe or spreading rapidly, fungicides containing propiconazole, iprodione, or thiophanate-methyl are effective. Research published in Plant Disease confirms that propiconazole applied at labeled rates provides reliable curative and preventive control of dollar spot across multiple turfgrass species.

For brown patch: Stop evening watering immediately — this single change often stops disease spread. Skip your next nitrogen application. For active infections, fungicides containing azoxystrobin, propiconazole, or trifloxystrobin are effective. Rotate between chemical families to prevent resistance.

When to call it something else

If your patches are irregular rather than circular, are expanding rapidly along edges of pavement or in the sunniest sections of the lawn, and if the grass peels back relatively easily from the soil — suspect chinch bugs rather than fungal disease. If the dead patches are scattered randomly and the grass lifts off the ground like a carpet — suspect grub damage. Both of these pest problems require completely different treatments from fungal diseases.