The Most Common Lawn Diseases – And How To Stop Them

Trying to identify the most common lawn diseases can be a challenge. This guide was created to give the knowledge on how to identify lawn diseases. After reading this article you will be able to identify: Does my lawn have a disease, which lawn disease, which course of action should be followed, and most importantly, how to prevent lawn diseases from coming back. Just like a three legged bar stool cannot stand if it is missing one of it’s legs, a disease cannot develop in a lawn if it is missing any of the three elements.

  • The Right Environment
  • A Pathogen
  • Susceptible Turf Grass
lawn mowing company logo

The Right Environment

The right environment for disease to grow in turf grass can be stopped with proper cultural practices. These include lawn aeration, proper mowing heights, proper fertilization levels, and adequate watering.

The right environment for diseases can be caused by heavy rainfalls, which we have experienced the last few years in Pennsylvania. On the other end, inadequate rain or proper irrigation can also be a breeding ground for diseases. Excessive thatch and grass clumps can also lead to lawn diseases. Bagging lawn clippings is one option, but this also robs the lawn of healthy natural fertilizer that grass clippings offer. Instead, adhere to proper mowing techniques such as never removing more than 1/3 of the grass blade when mowing. Following a weekly lawn mowing schedule is also very important to maintaining healthy turf grass. In addition, aerating the lawn twice a year, once in the Spring, and again in the Fall, will remove excess thatch buildup.


All lawns are susceptible to pathogens. Planting disease resistant turf grass is one of the most cost effective ways to prevent pathogen buildup. We use high quality turf grass designed by Pennsylvania State University that is specific to South Eastern Pennsylvania lawns. Pathogens are almost always in turf grass, but remain dormant until environmental conditions arise that activate the pathogens.

Susceptible Turf Grass

Turf grass becomes susceptible to pathogen activation when the proper environment gives way to susceptible turf grass. Turf grass becomes susceptible when heavy traffic, heavy rains or drought, improper fertilization, heavy thatch buildup and improper mowing conditions arise. To prevent this, be sure to have mower blades sharp, and to cut turf grass higher in the Spring and Summer. Only during the Fall and Winter should turf grass be cut below 3″ in Pennsylvania.

Disease Identification

Identifying the disease is the first step before treating it. Make sure that insects and pests are not the culprit before applying a fungicide. Check out our ultimate guide to the most common lawn pests in Pennsylvania in order to determine if pests or disease are causing the issues in your lawn. Lawn pests are much more common than disease on residential lawns.

Symptoms And Signs Of The Problem

Symptoms can appear as small, circular, tan lesions surrounded by purple or brown borders. This is known as leaf spotting. Tan, yellow, or red blotches covering most of the blade are known as blighting.

The species of turf grass that is being affected is also important to consider. Some species of turf grass are more resistant to pathogen outbreaks, while others are more susceptible.

The weather and site conditions play a major roll in an outbreak. High humidity, lots of sunlight, drainage conditions, soil conditions, and the amount of rain all play a factor. Poor mowing practices and improper fertilization can play a role in disease outbreak, as well as disease identification.

Common Lawn Diseases

Dollar Spot – 60-75 degrees F.

Dollar spot on a lawn
  • Most severe in high temperatures with inadequate rainfall. Inadequate fertilization will also contribute to dollar spot issues. White “cobwebs” which are the white mycelium of the fungi may be seen in the early morning when the lawn has dew still. Kentucky Bluegrass and Fine Fescue are the most susceptible. Proper cultural lawn practices will avoid dollar spot break outs.

Leaf Spot – Weather between 45-60 degrees F.

leaf spot on a lawn
  • Occurs when the lawn is being scalped (cut too low) during vital Spring and early Summer months. Over-fertilized lawns will make this problem more severe. A dark purplish-red oval border around the disease will appear as it worsens. All cool season turf grasses are susceptible. Avoid lawn scalping, over fertilizing, and frequent light watering.

Snow Mold – 32-45 degrees F.

snow mold on lawn image
  • Occurs in the Fall and Winter. Grass that is left too high during these months will produce snow mold. Perennial Ryegrass and Tall Fescue are the most susceptible. Proper mowing in the Spring and adequate fertilizer will revive turf from snow mold. While the blades of the turf may look dead, the crown and root are not. This is one of the most common lawn diseases, and tends to resolve itself naturally with no fungicides. Make sure to cleanup all leaves in the fall and early winter to avoid this! contact us today for a leaf removal service.

Yellow Patch – 32-45 degrees F.

  • Excessive thatch creates the perfect environment for patch. Patch diseases are almost always caused by excessive thatch. Occurs during the Fall, Winter and early Spring when low temperatures are around 40 degrees. Kentucky Bluegrass and Fine Fescue are most affected. While this is not one of the most common lawn disease for residential lawns, it is commonly found on golf course greens. Light fertilizer in the spring should restore the turf.

Red Thread – Weather between 45-60 degrees F.

Red thread, as the name indicates, can be identified by pinkish-red threads sticking out of the leaf blade. The leaves will at first become red, and then fade out to a bleached straw color. Affects all cool season grasses, especially perennial ryegrass and fine fescue. To prevent red thread, cut turf at proper mowing heights and practice weekly lawn maintenance. Prolonged periods of dampness will help trigger red thread.

Pythium Blight – Hot Temperatures, above 75 degrees F.

pythium blight on a lawn image
  • Excess watering and poor drainage contribute pythium blight. High humidity where water tends to pool up, or not drain properly can affect All Cool Season Turfgrasses. Improve the air quality and drainage to rid lawns of blight. Sometimes called “grease spot” because of the greasy leaves and look that is characteristic of pythium blight.

Fairy Rings – Hot Temperatures, above 75 degrees F.

  • First appear as a cluster of mushrooms or toadstools. These will appear on the outer edge of what forms a ring. The rings can form as either dark green and fast-growing turf, or as slow growing killed turf. High soil moisture and hot temperatures contribute to fairy rings. All cool season grasses can be affected. These symptoms can be masked by core aeration, and moderate fertilization. Fungicides may need to be used as a preventative measure next season if this is a reoccurring problem.

Preventing The Most Common Lawn Diseases

Similar to the treatment of broadleaf weeds and lawn pests, lawn diseases work best with prevention methods. The best “defense” is a strong offense! Go on the offensive this year. Aerate in the spring and fall, cleanup any leaves in the fall and winter, fertilize with pre-emergent early (I recommend March for first treatment). Keep your mower deck in the correct range for the season (3-4″ in the spring and summer, 2.75-3.5″ in the fall and winter). Keep those blades SHARP! We change our blades regularly because slow blades not only slow your mowing down, they can cause a host of issues.

To prevent lawn diseases:

  • Core Aerate
    • Removes thatch, opens up air flow, creates stronger roots.
  • Follow Healthy Lawn Mowing Practices
    • Sharp blades, proper mowing heights for the season, not scalping the lawn.
  • Proper Lawn Fertilization Levels
    • Over fertilizing can actually burn the lawn, stressing it even further. This is why dog urine “burns” the lawn. Urine is high in nitrogen content and creates yellow spots on a healthy lawn. Follow the directions on the label for proper fertilizing, and make sure to have your spreader/sprayer calibrated correctly.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: