Dog Spots or Lawn Fungus? How to Tell the Difference

Round brown spots in the lawn. Is it the dog, or is it a disease? People spray fungicide on dog spots and blame the dog for fungus all the time. A couple of quick checks will tell you which one you've got.

The ring test

Look at the edge of the spot.

• Dog spot: a brown or straw-colored center with a ring of extra-green, lush grass around it. The middle got too much nitrogen and salt all at once and burned. The edges got a light dose, like fertilizer, and grew greener.
• Fungus: often a brown or tan patch without the dark green ring. Some diseases show a darker or smoky edge, or a ring of dying grass, but not that lush green halo.

The tug test

Grab some brown grass in the middle and pull gently.

• Dog spot: roots are usually still attached. The grass is burned, not chewed.
• Grubs: the turf lifts up like a loose carpet, roots chewed off. See fall grub damage.
• Disease: varies, but look at the blades. Lesions, spots, a web or fuzz in the morning, or dark specks point to fungus.

Where and when

• Dog spots show up where the dog goes: near the door, along the fence, in the same part of the yard over and over. They appear year-round, and stand out more in dry spells.
• Disease follows the weather: hot and humid nights for brown patch, cold and wet for snow mold. It often shows up in several places at once after a stretch of that weather. See brown patch diagnosis and gray vs. pink snow mold.

Fixing dog spots

• Water the spot right away after the dog goes, if you can. Diluting it prevents most burns.
• Train a spot. A mulched or gravel area for the dog saves the lawn.
• Rake out the dead grass, loosen the soil, and reseed. Perennial ryegrass and tall fescue tend to handle it better than Kentucky bluegrass. In fall, that may mean dormant seeding or waiting for spring.
• Skip the supplements that claim to change your dog's urine unless your vet says so.

Fixing fungus

Usually the fix is the conditions, not a spray. See fungicide on a home lawn is usually the wrong fix.

When in doubt, your state's extension plant diagnostic lab can look at a sample for a small fee.

Photo: Prob. brown patch of Centipedegrass (Eremochloa ophiuroides) caused by Rhizocton by Plant pests and diseases, CC0.