Summer Disease Control in Cool Season Lawns

The summer is upon us and many of us are excited for warmer weather. Unfortunately, summer is also the prime time for disease outbreaks in cool season lawns. Cool season lawns are usually located in the transition zone and northern regions of the United States while warm season grasses can grow into the transition zone and southern regions of the country.

Warm season lawns tend to be prone to disease the most during the spring and the fall. Cool season grasses, however, are more prone to diseases during the summer. Diseases in both types of grasses can still take place any time of the year. 

Here is a list of few cool season grass types:

• Kentucky bluegrass,
• Perennial and annual ryegrass,
• Tall fescue,
• Fine fescue,
• Bentgrass.

Learn more about warm season vs. cool season grass and the regions they grow in here. 

What is a lawn disease?

Your natural lawn is a living product. This means you have to feed it, water it and perform other maintenance tasks to keep it healthy and thriving. 

Most lawn diseases are caused by a form of fungus. The fungi need to obtain energy as a means of feeding off of either dead organic matter (and convert the nutrients in dead organisms into energy) or find and take over a host plant. Some common locations you will find fungi in your lawn will be under dead leaves, the shade or in excessive thatch.

Fungi spread through spores, which are easily transferred through wind, rain, mowing and simply walking through a fungi outbreak. 

For fungus to spread and be present, there needs to be three main factors, also known as the disease triangle:

a) a host, living or dead organic matter (thatch and leaves),

b) the right environmental conditions, such as shaded, moist areas to grow in,

c) and the pathogen.

All three must be present for the fungus to grow and spread. Learn more about the disease triangle and what a fungus is here. 

Now, let’s take a look at some of the most common cool season lawn diseases.

Brown Patch

Appearance/Symptoms:

• Large patches of dead grass,
• Thin, circular patches of brown grass,
• Brown, tan or yellow in color.

Causes:

• Hot, humid weather,
• When blades are continuously wet for an entire day or more,
• Poor soil drainage,
• Lack of air movement,
• Shade,
• Cloudy weather,
• Dew,
• Over-watering,
• Watering in late afternoons.

Affected Grasses:

• Most common in tall fescue located in the southeast where temperatures are warmer,
• Ryegrass,
• Bentgrass,
• Bluegrass.

Recommended Treatment:

Read product labels thoroughly before application.

Dollar Spot

Appearance/Symptoms:

• Small, bleached round spots,
• Spots range between 5–6 inches in home lawns,
• Tan-ish color that looks similar to straw,
• Leaves begin to die after becoming girdled on the surface,
• You may also see short, fuzzy, mycelium forming on the turf.

Causes:

• Temperatures higher than 50 degrees Fahrenheit ,
• 10–12 consistent hours of leaf wetness or moisture,
• Lawns with a lower level of potassium usually have poor tolerance against dollar spot,
• Excessive thatch and frequent irrigation.

Affected Grasses:

You may find dollar spot on a wide variety of turfs. The most common are:

• Bentgrass,
• Perennial ryegrass,
• Kentucky bluegrass,
• Bermuda grass.

Treatment:

Read product labels thoroughly before application.

Fairy Ring

Appearance/Symptoms:

• Patches, rings, or arcs of dead grass,
• Dark green in color,
• Grows faster than surrounding turfgrass,
• Mushrooms or puffballs that grow in arcs or rings.

Causes:

• Thatch,
• Drought stress,
• Poor irrigation,
• Infrequent aeration,
• Nitrogen or iron nutrient deficiencies,
• Heavy or frequent rainfall.

Affected Grasses:

• All grasses can be affected by fairy ring.

Treatment:

Read product labels thoroughly before application.

Powdery Mildew

Appearance/Symptoms:

• White grayish spots, 
• Powdery-looking substance,
• Overtime, it can expand and product large white or gray spots.

Causes:

• Reduced air circulation,
• High levels of humidity,
• Low light,
• Temperatures between 60–70 degrees Fahrenheit but less than 90 degrees Fahrenheit.

Affected Grasses:

• Kentucky bluegrass,
• Fine fescue, 
• Perennial ryegrasses.

Treatment:

Read product labels thoroughly before application.

Pythium Blight

Appearance/Symptoms:

• Dark patches,
• Greasy/gray colored layers,
• Light brown surface formation,
• Cotton-like growth,
• Patchy surfaces.

Causes:

• Humid weather,
• More common when temperatures exceed 90 degrees Fahrenheit,
• Outbreaks can still occur when temperatures are at 68 degrees Fahrenheit or higher,
• Low light,
• Improper irrigation practices,
• Watering at the end of the day,
• Standing water,
• Thatch.

Affected Grasses:

• Perennial ryegrass – high chance,
• Creeping bentgrass – high chance,
• Annual bluegrass – high chance,
• Kentucky bluegrass – higher resistance but can still get infected,
• Tall fescue – higher resistance but can still get infected,
• Bermuda grass  – higher resistance but can still get infected.

Treatment:

Read product labels thoroughly before application.

Summer Patch

Photo Credit: University of Massachusetts Amherst.

Appearance/Symptoms:

• Circular patches or rings,
• A size of 6 inches to 3 feet in diameter,
• Off-colored at first then turns yellow or tan,
• Wilting,
• Poor growing,
• Sunken turf,
• Outer edges may be orange, 
• Turf should be easy to pull up when infected,
• Rotted roots, crowns or rhizomes.

Causes:

• Heat,
• Drought stress,
• Excessive nitrogen,
• Potassium deficiency,
• Poor drainage,
• Over-watering,
• Thatch,
• Compaction. 

Affected Grasses:

• Creeping bentgrass,
• Annual bluegrass,
• Kentucky bluegrass,
• Fine fescue.

Treatment: 

Read product labels thoroughly before application.

Cultural Prevention and Treatment of Lawn Disease

Having a healthy lawn is your best line of defense against turfgrass disease. Lawns that are properly fed, watered in mornings, mowed at the right height, regularly aerated and dethacthed, have access to light, located in places with air flow are more likely to 1) better resist disease outbreaks and 2) fight off disease when infected. 

Providing your lawn with essential nutrients is vital to maintaining a healthy, strong lawn. Sod Solutions recommends the Lawnifi® Fertilization Program. Lawnifi gives your lawn what it needs in the form of nano-sized nutrients, exactly when it needs it in the form of easy-to-apply monthly applications from March through November.

It’s important to note that even with the use of an improved fertilizer program, the timely application of fungicide is still necessary for overall lawn health. If you fertilize your lawn with nitrogen before applying a fungicide and presently have a lawn fungus, that fungus will expand exponentially, which can be disastrous for your lawn.

Chemical Prevention

If your cool season lawn has experienced disease around a certain time of year before, be proactive and apply a disease control product at a preventive rate before disease takes hold. Learn more about preventive applications here.

Disease Control Rotations

If problems with a certain lawn disease persist, consider rotating fungicides with different active ingredients as the disease may have built up an immunity to one active ingredient over time. Be sure to read product labels thoroughly before application.

Finally, if you aren’t sure if your lawn is caused by disease or some other external stressor like drought or insects, submit a sample to your local extension office for proper diagnosis. Learn to tell the difference between other common diseases in our blog on Identifying Common Lawn Diseases.

Sources:

• https://www.turffiles.ncsu.edu/diseases-in-turf/fairy-ring-in-turf/
• https://content.ces.ncsu.edu/summer-patch-in-turf