In the Pacific Northwest, lawn fungus affects all types of grass and occurs in a variety of weather conditions. From cool, wet weather of fall and winter to warm periods of the summer, this fungus can turn your beautiful yard into a brown patch of dead grass, and it can be a nightmare to eliminate.

So how can you ensure a healthy, green yard this year? While no grass is completely disease-proof, you can control the spread of fungal disease in your yard through proper identification and lawn care treatment. Let’s take a look at what causes lawn fungus, how to identify it, and what you can do to eliminate it.

What causes lawn disease?

Garden lawn with unhealthy brown dead patchesBiologically speaking, your lawn naturally contains fungi and spores, but these microorganisms are not exactly problematic until certain conditions have been met. For lawn fungus to occur, the following factors must be present:

  • A harmful pathogen (i.e. a bacterium that causes disease)
  • The right environment (i.e. air temperature and water quantity in your yard)
  • Host (i.e. grass that is susceptible to the existing pathogen)

It’s important to note that there are many different causes of brown grass, but it doesn’t always mean you have lawn disease. A stressed yard, for example, is often mistaken for fungal disease because it also discolors the grass, and if left untreated, it can make your lawn more susceptible to disease.

The following items can stress your yard and make it more prone to developing lawn fungus:

  • Overwatering
  • Irrigation problems or poor drainage
  • Extreme weather conditions
  • Excessive fertilization
  • Compacted soil
  • Improper mowing (i.e. cutting too low)
  • Drought
  • Dog urine
  • Herbicides
  • Heavy thatch

To protect against the development of fungal disease in the Pacific Northwest, promote a stress-free environment for your yard through regular maintenance and care (i.e. watering, fertilizing, etc.).

Identifying & Treating Lawn Fungus

Successful disease management hinges on selecting the appropriate grass type for your specific area and climate. In Washington State, here are some of the most common lawn diseases and their recommended treatments1:


1. Fusarium Patch

  • Color: Tan or brown
  • Size and appearance: Small (2-12 inches), circular patches
  • Location: Eastern and western Washington
  • Most vulnerable grass type(s): Bentgrass, annual bluegrass, and others
  • Environment: Thrives in cool, moist weather conditions

Treatment: Use a 3-1-2 or 6-1-4 ratio of nitrogen (N), phosphorus (P), and potassium (K), or NPK. You may need to apply fungicides.


2. Leaf (Stem) Rust

  • Color: Yellow, orange, red, brown, or black
  • Most vulnerable grass type(s): Kentucky bluegrass
  • Environment: Results after heavy dews in warm weather

Treatment: Because rust grows upward toward grass tips, treatment is best suited by mowing and applying 1 lb of nitrogen per 1,000 square feet. Water and fertilize as necessary.


3. Red Thread

  • Color: Pink, brown, or light tan in dry weather; red in wet weather
  • Size and appearance: Various sizes/shapes; may be burnt in appearance
  • Location: Eastern and western Washington
  • Most vulnerable grass type(s): Fescues, ryegrass, and bentgrass
  • Environment: Thrives in cool, wet weather

Treatment: Use 3-1-2 or 6-1-4 ratio of NPK and apply treatment during the fall and winter. Be sure to mow the grass, water regularly, and add calcium as needed. In extreme cases, you may need to use fungicides.


4. Powdery Mildew

  • Color: Gray and white; may appear yellow if leaves are dying
  • Size and appearance: Small, powdery blemishes on leaves and grass stems
  • Location: Eastern Washington
  • Environment: Mild, warm conditions, especially in areas of shade

Treatment: Allow more sunlight to pass through to the infected area and increase air circulation. Fertilize, water (preferably in the morning), and cut at a higher lawn mower height. Red or Chewings fescues work best in shady areas.


5. Take-all Patch

  • Color: Brown or gray
  • Size and appearance: Round dead spots approximately 4-36 inches in diameter; usually surrounded by weeds
  • Location: Primarily in western rather than eastern Washington
  • Most vulnerable grass type(s): Bentgrass
  • Season: Late spring and summer

Treatment: Fertilize using ammonium sulfate or other equivalent material. Be careful not to apply excessive amounts of lime and or water.


6. Necrotic Ring Spot

  • Color: Yellow, brown, or black
  • Size and appearance: Dead rings or arcs up to several feet across; may be invaded by weeds or healthy bluegrass
  • Location: Eastern and western Washington
  • Most vulnerable grass type(s): Kentucky bluegrass
  • Environment: Areas of shallow top soil and rock-filled sub-soil
  • Season: Primarily spring and fall, but sometimes most of the year

Treatment: Best treated by hiring a turf specialist. Keep your thatch layer at a moderate thickness and avoid over-watering and over-fertilizing your lawn.


For more information about lawn diseases or if you’d to schedule a turf specialist to examine your grass, contact us today.


1Source: Home Lawns, an extension of Washington State University.