Common Lawn Diseases found in Minnesota Lawns

Fusarium Blight

Fusarium Blight in Lawns

Fusarium Blight is a turf fungus that has become more common in Minnesota lawns. Fusarium Blight generally attacks sodded lawns that are 3 to 7 years old, and in some cases older. Occurrence period is summer to late summer. Stress, compaction, drought and high temperatures  (above 80) enhance symptom expression. Maintaining proper cultural practices is essential when dealing with fusarium blight.

Leaf Spot

Leaf Spot in MN lawns

Leaf spot is a fungus that effects all cool-season grasses. Affected grass blades have purplish lesions with tan centers. Advanced stage (melting out) is caused by crown rot which thins turf and turns entire area brown late summer. Occurrence period is spring and fall. A dull mower blade, cool, overcast, and/or moist conditions can contribute to an outbreak. Poor cultivars of Perennial Ryegrass are often affected by this.

Dollar Spot

Minneapolis Leaf Spot Lawn

Dollar spot causes (1-6″) circular patches of bleached turf. A (cobweb) white fungal growth may appear and be most visible early in the morning when dew is present. Occurrence period is spring and summer. Humid conditions and temperatures between 60-80 are favorable for the fungus. Bag mowing clippings for a couple mowings if fungus is detected.

Powdery Mildew

MN Lawn Powdery Mildew

Powdery Mildew appears as a white to gray powdery growth on grass blades. Turf may thin out with prolonged exposure. Occurrence period is spring to fall. Low light, reduced air circulation and temperatures between 55-72 promote fungal activity. trimming trees and/or shrubs and maintaining adequate fertility will improve conditions. This is often seen in Kentucky Bluegrass (sod) that is grown in shady areas.


Rust in MN Lawns
Rust affects all cool-season grasses. Affected areas are covered with yellow-orange to reddish-brown dust. Prolonged exposure can cause turf to yellow, wither and die. Occurence period is mid summer to fall. Warm nights, wet leaves and low light intensity promotes activity. Most severe when turf is not actively growing or is under stress. Often times, when you walk over a Rust affected are you will have orange rust spores on your shoes.

Pink and Gray Snow Mold

Snow Mold in MN

Snow mold is a fungus that effects all cool-season grasses. Areas affected appear bleached and/or pinkish and grass may be slimy and matted. Occurrence period is early spring. Once ground thaws, lightly “fluff” area using a stiff broom to allow proper air flow to the plant. Generally no reseeding is needed as when the lawn dries out, the Snow Mold will dissapear.

Fairy Ring

Fairy Rings in MN Lawns

Fairy Ring appears as a dark green circular patch or ring 4 to 8″ wide that grows faster than surrounding grass. With time the circular patch may die and mushrooms can appear. Typically shows up in an area that a tree was removed. Decaying wood is the common source of the fungus. Occurrence period is early spring to late fall. Removal and replacement of infested soil will be necessary to solve the fungal problem.


Mushrooms in MN Lawns

Mushrooms are a fungus that generally appear when temperatures are mild and ample moisture is available. Decaying organic matter is a common source of the fungus. There is no effective control for mushrooms. Hand removal is the best solution. In nearly all cases, these will not impact the lawn and subside once moisture is reduced.

Red Thread and Pink Thread

Red Thread in MN Lawns

A fine pink to red appearance indicates active fungi. Affected area is small, between 2″-6″.  Occurs most often in cool, moist conditions. (heavy dew, fog, drizzly rains) Typically occurs in early spring and again in fall. Affects Fescue, Ryegrass, Bentgrass and Kentucky Bluegrass. Fungicides are available but are expensive and often unreliable. This is a self correcting disease by using correct cultural practices. Easy detection is found by Pink fungus growing off the tips of the grass blades.

General Cultural practices for Diseases

Thatch Layer – The thatch layer is the layer of decomposed or partially decomposed organic material between the green part of the plant and the soil. Never allow the thatch layer to accumulate to over 1/2″ thick. If the thatch layer is over 1/2″ we recommend to power rake or aerate the lawn. It is also a good idea to aerate the lawn every September and overseed damaged areas with a good quality seed immediately afterwards.

Water – Try to put down 1″ of water on the lawn every other day when the weather is hot and dry or approximately 3″ a week minimum. Never water at night as the standing water are a great breeding ground for disease. Don’t allow the lawn to dry out at any time during the season. When seeding, water consistently for six weeks, or until seedings are mature.

Mowing – Never mow more than 1/3 of the plant blade off at any time during the season. Set mowing height at 3 – 3 1/2″ during the hot and dry months. Always keep your mowing blade sharp. Do not mow if the temperature is at or above 90 degrees. Try to water immediately after mowing.

Fertilizing – Proper fertilizing is important for certain diseases. Applying the  proper amounts of fertilizer throughout the year is imperative to promote a strong root system and disease tolerance. Many diseases thrive in under or over fertilized turf.

Please remember your part is just as important as FERTILAWN’s in caring for your lawn. Feel free to call at any time throughout the year with any questions.

Your Lawn. Our Passion.