Common Lawn Diseases

Common Lawn Diseases in Minnesota

​Lawn diseases can be hard to identify, particularly if you're not aware of the symptoms. Recognizing the signs early can help you prevent more extensive damage to your lawn. Here is a list of the most common lawn diseases found in Minnesota.

Ascochyta Leaf Blight
Ascochyta Leaf Blight is a stress-induced fungal disease found in lawns. It causes straw-like and bleached irregular patches in the grass that appear rapidly, oftentimes overnight. If you inspect infected blades of grass, you will notice that they look dead on the top and in the middle but are still green near the root. It is possible that you may also notice very small, dark brown spots on the blades. It is very uncommon for roots to be affected. (Photo: Note that the lawn was infected by Ascochyta Leaf Blight and subsequently spread after a mower operated on the lawn, causing the appearance of "tracks").

Dollar Spot
Dollar Spots are an invasive fungus that present as sunken patches which are very small and circular. Most frequently, the spots are the size of a silver dollar but can reach up to six inches in diameter on taller turf. Like many other lawn diseases, the Dollar Spots are straw-colored. However, they can initially appear as brown and are often found in clusters. As the clusters grow, they can become irregular patches and less circular shaped.

Brown Patch
Brown Patch is an invasive fungus that also causes patches of brownish-yellow grass (however, these patches differ from Dollar Spot in that they are irregular shaped and much larger). These patches often start around six inches in diameter but have been known to easily grow to multiple feet in diameter (sometimes even more than 10 feet). Brown Patch most commonly occurs in higher temperatures and higher humidity levels. ​

Leaf Spot
Leaf Spot presents as circular brown lesions on blades of grass. Grass infected by Leaf Spot will begin to appear yellowish and start to wilt, which often causes homeowners to incorrectly assume that their lawn is affected by drought stress. Subsequently, homeowners will over-water their lawn causing the disease to spread further. Unfortunately, Leaf Spot often spreads to the root of your grass and can kill portions of your lawn. It thrives in warmer temperatures and requires high levels of moisture to survive. 

Necrotic Ring Spot
Necrotic Ring Spot initially presents as light green patches in lawns that range in size from a few inches to multiple feet in diameter. These patches can be spread throughout the yard or be centralized to a small portion. At first glance, this lawn disease can be difficult to distinguish from other patch diseases. However, these patches gradually develop into bronze or straw-colored rings, with healthy, green grass in the center. This often creates a “donut” or “frog-eye” appearance. ​

Red Thread
Red Thread is a fungal lawn disease that is easily identifiable by its pinkish-red thread-like strands of fungal mycelium. This lawn disease often develops during sustained periods of humid or rainy weather, and flourishes in temperatures between 40 degrees to 80 degrees. Red Thread can weaken your lawn and cause it to be more susceptible to other diseases, but it will not kill your lawn. Oftentimes, the grass affected by this condition will recover in a few weeks time. ​

Powdery Mildew
Powdery Mildew is a fungus that causes turf to appear as though it was dusted with flour, giving infected turf a “powdery” appearance. This lawn fungus can occur on a vast variety of grass species, and thrives in elevated humidity, shaded-areas, and areas with limited air circulation. Powdery Mildew can also affect healthy plants (such as flowers, vegetables, and fruits). Unfortunately, severely infected grass will eventually turn yellow/brown and begin to die.

Pythium Blight
Pythium Blight presents as small dark patches in turf (often appearing black, orange, or purple in color). The small patches typically grow into much larger, irregular areas (and are often found on golf courses). Pythium Blight spreads quickly in ideal conditions: high temperatures, high moisture, and decreased air movement. This lawn disease is often called “grease spot”, as infected areas are often greasy in appearance. Unfortunately, like many other turf diseases, this can spread rapidly by being tracked by lawn equipment.

Rust Disease
Rust Disease is easily identifiable because it causes an orange or rusty-colored powdery substance on blades of grass. The infected turf initially appears to have small, yellow spots but the spots quickly rupture into the powdery “rusty” residue. Unfortunately, this lawn disease spreads easily and often sticks to shoes, pets, and lawn equipment. Rust Disease can occur anytime through Spring and Fall - and with all lawn fungi, thrives in wet and humid environments.

Snow Mold
Snow Mold is a common fungal lawn disease that forms when snow or wet leaves cover turf for an extended period of time. The damage is typically noticed by homeowners in the Spring after the snow begins to melt. Snow Mold (both Pink and Gray) have a fuzzy, web-like appearance, typically in circles ranging from a few inches to a few feet in diameter. The grass in these affected patches will typically become matted down and straw-colored.

How to Prevent

At West Metro Lawn and Snow, we support a natural approach to correcting these common lawn diseases. This is because fungicide treatments kill both the bad and the good bacteria in your lawn, leaving your lawn far more susceptible for the fungal issues to reoccur in the future.

Here are a few of our top recommendations on how to help your turf fight back:

• Mow Regularly (and Correctly). Ensure that your lawn is being mowed regularly and at the appropriate height. Grass that is allowed to grow too tall (or that is cut too short) is more susceptible to lawn fungus. 
• Water Deeply but Infrequently. Water your lawn deeply but less frequently. This encourages deep root growth, making your grass more resilient to fighting off fungus and disease. In addition, be sure to water in the early morning (versus evening - as moist conditions overnight can promote the development of fungal disease).
• Fertilize Regularly. Regularly fertilizing your lawn will help to promote healthy turf growth and a lawn that is less likely to develop lawn fungus and disease throughout the Green Season.

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