Lawn Fungus

Lawn Fungus admin February 21, 2023


What are the Most Common Lawn Diseases in Colorado?

The two most common lawn fungus problems that we see in Colorado, especially the Boulder and Fort Collins areas, are Necrotic Ring Spot and Ascochyta Leaf Blight. Less common lawn diseases in Colorado include: brown patch fungus, dollar spot fungus, powdery mildew, pink and grey snow mold, and melting out. Common insect pressures in lawns include sod webworms, clover / spider mites and white grubs.

Before applying any chemicals or fungicides, the first step in the treatment of a lawn disease is to properly identify what is causing the lawn disease. About 99.99% of the time when we investigate a lawn problem for a customer, the lawn disease is being stimulated by improper lawn watering.

At Organo-Lawn we have state licensed lawn care professionals with many years of experience in lawn care and grass disease identification. Always call Organo-Lawn to schedule a disease diagnosis prior to applying potentially dangerous and unnecessary lawn fungicides to a lawn.

Our lawn care experts can diagnose your lawn problem and will be able to explain why most lawn diseases are easily fixed with minor adjustments to the sprinkler system.

Ascochyta Leaf Blight

Ascochyta Leaf Blight

Dog Urine Damage

Dog Urine Damage



Necrotic Ring Spot Fungus

Necrotic Ring Spot Fungus

Snow Mold

Snow Mold

Vole Damage

Vole Damage

Additional Colorado Lawn Fungus and Disease Problems

Brown Patch - Boulder CO

Brown Patch Lawn Fungus

Brown patch is not a major problem of lawns in humid areas, but the low humidity of our Colorado climate helps prevent this common disease of lawns. When there is a case of brown patch in lawns in Colorado it is usually in a very shady area that is being severely over watered. The most susceptible grass types to brown patch include perennial ryegrass, tall fescue, and the bentgrasses. Occasionally, brown patch becomes a problem on Kentucky bluegrasses in mid- to late summer during extended periods of high temperature and humidity. Brown patch is easily controlled on Colorado lawns by watering according to the 1-2-3-2-1 lawn watering technique, core aeration, and proper organic fertilization. The application of fungicides or lawn chemicals is completely unnecessary. The low humidity in Colorado is very beneficial in preventing outbreaks of brown patch.

Dollar Spot Fungus

Dollar spot is almost identical to Ascochyta Leaf Blight and they are both a symptom of shallow grass roots. For most people there really is no difference between Dollar spot and Ascochyta Leaf Blight. Dollar spot is a lawn fungus named for the straw colored, circular patches it creates on your lawn that are about the size a silver dollar coin. This common lawn fungus is the sign of shallow grass roots and it only attacks leaf blades, and does not attack the crown or the roots. This is important because this means the fungus cannot kill the grass and it will only discolor the blade of grass.Treating dollar spot is very simple. Audit the sprinkler system and change the lawn watering technique to the 1-2-3-2-1 lawn watering principals. After the sprinkler audit, water the lawn deeply for 3 consecutive days and then go back to the 1-2-3-2-1 lawn watering technique. Chemical and fungicide treatments for dollar spot are completely unnecessary and should not be applied.
Dollar Spot Fungus - Ft Collins
Fairy Ring Fungus

Fairy Ring Fungus

Fairy rings are caused by a family of soil-inhabiting fungi called basidiomycetes. Symptoms appear in lawns as dark green circles and they range in size from a few inches to 200 feet or more in diameter. Dark colored rings of turf are formed by the release of nitrogen and other nutrients by the fungi that are feeding on decaying organic matter in the soil. It is common to see a circle of mushrooms around the edge of the infected area. Fairy rings are a symptom of a thatch problem in a lawn. Thatch develops in a lawn that is not being watered properly. Fairy rings can grow at the rate of 6 to 24 inches annually depending on environmental factors. Fairy rings are not very common in Colorado because they are not as prevalent in clay soils, as they prefer sandy soils that are low in water and fertility. The best treatment for fair rings in a lawn are to perform a double lawn aerationstimulate beneficial microbial activity in the soil with organic fertilizer treatmentshumate soil conditioner applications, and watering the lawn according to the 1-2-3-2-1 lawn watering technique. Fungicide or chemical treatments are not necessary in preventing and treating fairy rings.

Fusarium Blight

Fusarium Blight is more commonly known as Necrotic Ring Spot. Fusarium blight is caused by the fungi Fusarium roseum and F. tricinctum. The disease is most troublesome on cool season grasses, especially bluegrass lawns. This disease is a clear indication of severe over watering of the lawn for a long period of time. The fungus causes necrosis in the roots which show up as doughnut-shaped rings that can be up to 3 feet in diameter. The center is usually healthy green grass giving a frog-eyed pattern to the diseased area. This distinctive look is why some people call this the frog-eye fungus. Fusarium Blight did not occur in the lawn overnight and was caused by gross over watering of the lawn and is a clear symptom of a completely dead soil. To repair a lawn with severe fusarium blight will take anywhere from 1-2 years. The first step is to change the watering to follow the 1-2-3-2-1- lawn watering technique, and then rebuild the microbial population in the soil with a combination of core aeration, high quality organic fertilizers and humate soil conditioner applications. Fungicides should never be applied to a lawn with fusarium blight because they will slow the recovery process.
Fusarium Blight
Glyphosate Damage on a Lawn

Glyphosate Damage to Grass

Is there a new exotic disease infesting lawns, or do these “exotic diseases” often have a much simpler explanation? The photo to the left is a great example of why lawn care is something that should be left to professional yard care companies. Glyphosate damage in lawns happens a lot and here is a story from one of our lawn care customers… This customer had weeds growing in their lawn, their son thinking he would be helpful went and grabbed weed killer from the garage and decided to spot spray all of the weeds in the lawn. About 10 days later the homeowner started seeing these strange circles “growing in the lawn,” Unable to identify what was killing the grass, they gave us a call saying they have a lawn disease that just appeared all of the sudden. When we get out there, we saw that this was no lawn disease we had seen before. We let them know that those dead areas were from some sort of chemical being put on the lawn. The customer told us that nothing of the sort had been done. We asked him if he or anybody in the house had spot sprayed the lawn using Roundup. He said, “absolutely not!” A few days later they called us back to say that their son admitted to spot spraying Roundup on all the weeds in the lawn. Oops!

Melting Out Disease

Melting Out disease is sometimes called leaf spot. This problem occurs in lawns that are stressed from excessive applications of chemical nitrogen fertilizerimproper lawn watering, and very short lawn mowing height. Two separate fungi cause the lawn discoloration, but, because the diseases usually occur together, they’re considered a single disease complex by experts. Leaf spot symptoms include very small, purple or lack spots on individual leaf blades. The elliptical spots may be surrounded by a purple border. Tissue in the center of the spot often dies and turns a straw color. If a disease extends across the leaf, the blades wither and die. Leaf spot is more common on lawns that were seeded or sodded prior to 1980, because the bluegrass varieties used during that time had relatively poor resistance to leaf spot. Newer bluegrass varieties are very resistant to leaf spot. Some lower quality bluegrass varieties sold in “big-box” stores are susceptible to this disease and should be avoided. Older lawns suffering from this disease should be seeded with high quality seed varieties instead of being treated with fungicides. Preventing this disease is easy if the lawn is being care for with high quality organic fertilizers and organic weed controls, is being mowed tall and watered according to the 1-2-3-2-1 lawn watering technique.
Melting Out Disease on Grass
Poor Sprinkler Coverage - Boulder CO

Poor Sprinkler Coverage

Improperly adjusted sprinkler heads that leave large gaps when watering lawns is one of the biggest lawn care problems of Colorado. About 60% of brown spots in lawns are caused by poor sprinkler coverage. During the hot summer months of June, July and August and during prolonged periods of drought are when brown spots appear in the lawn. Many homeowners assume that a brown spot in the lawn is a disease or fungus, but the majority of the time the brown spots are related to sprinkler heads that are blocked by plants, are not functioning properly, or are not correctly adjusted. To recover a brown spot caused by poor sprinkler head coverage is easy. Start by adjusting or fixing the sprinkler head coverage issue and then water the brown spot for 3 consecutive days, followed by watering according to the 1-2-3-2-1 lawn watering technique. If the area cannot be watered properly with the irrigation system, hand watering with a hose and sprinkler head will fix the dry spot.

Powdery Mildew on Grass

Powdery mildew in lawns is usually the result of grass that is growing in an area with poor air circulation. This minor lawn fungus starts with small light spots on the blades of grass. As the disease progresses, almost the entire blade of grass will turn white and it looks as though the lawn has been sprinkled with talcum powder. Powdery mildew develops in shady locations that have poor air movement. Colorado is a very dry climate and lawns that have reoccurring outbreaks of powdery mildew indicate that the lawn is not being watered according to the 1-2-3-2-1 lawn watering technique. Pruning trees to reduce shade helpful in increasing the amount of sunlight that reaches the grass. If the lawn area is in constant shade, consider covering the area with attractive mulch. The area under a tree is perfect for a mulch-covered shady retreat with garden seating and potted shade plants. Powdery mildew will not damage the crown of the grass and therefore it is not necessary to treat the lawn with a fungicide or chemical lawn treatment. Improving air flow and following the 1-2-3-2-1 lawn watering technique are the best defenses for preventing powdery mildew.
Powdery Mildew on Grass
Power Rake Damage

Power Rake Damage to Grass

Power raking or thatching a lawn after the grass had started to green up can cause serious damage. Most lawns do not need to be power raked because they do not have an excessive thatch layer. Many lawn care companies do not understand what power raking a lawn accomplishes and they offer this unnecessary lawn care service to customers. Damage to the lawn can occur if the power rake is performed after the lawn has started to green up for the season. If a lawn is suffering from an excessive thatch layer a better method for controlling the thatch problem is to stimulate beneficial microbial activity in the soil. The reason that the thatch is accumulating is because there is an absence of microorganisms that feed on the organic matter. Power raking a lawn is only necessary in the most extreme cases. Lawn damage caused from a power raking or thatching that was performed too late in the season will usually take 1-3 months to recover. Proper lawn mowing, using high quality organic fertilizersproper lawn watering, and core aeration will help the lawn recover faster. Always consult with a professional lawn care company prior to power raking a lawn.

Rust on Grass

Rust in lawns appears as orange powdery spores growing on grass blades. This is a fairly uncommon lawn problem in Colorado due to our extremely dry climate. If we do see rust growing on lawns it tends to be after rainy or humid weather. Rust us usually noticed after the orange postules rub off onto shoes, clothing or feet. Rust spores can easily be tracked into homes. Cool nights with heavy dew and light, frequent rainfall or irrigation create ideal conditions for rust to develop. Watering according to the 1-2-3-2-1 lawn watering technique will help prevent rust from developing in grass. Rust typically does not cause severe problems on lawns but they may weaken turf grasses and make them more susceptible to other problems like heat and drought stress or other lawn diseases. Preventing and controlling rust is best accomplished through proper cultural practices. Lawns that are being watered according to the 1-2-3-2-1 lawn watering technique, are being mowed at three inches or taller, and are being fertilized with high quality organic fertilizers rarely suffer from rust pressure. Good airflow and proper sunlight are also important in preventing rust from growing on grass. Using fungicides or chemicals to control rusts on lawns are unnecessary.
Rust on Grass
Dog Vomit Slime Mold

Slime Molds on Grass

Foamy looking patches called slime molds may appear out of nowhere on lawns or mulch areas. It is common for these slime molds to appear after rainy periods, especially if temperatures are warm and humid. Slime molds come in all colors and can be white, gray, yellow, purple, orange or brown. Some people say the patches look like vomit from a dog or other animals which is where the name “dog vomit slime mold” may have originated. Slime molds are a group of fast-growing fungi and they are usually more unsightly than harmful. They don’t cause damage to the lawn. The slime mold fungi may actually benefit the plants by consuming potential pathogens and bacteria that could harm the plants. Slime molds are not unsightly and not considered to be dangerous to humans or animals. Chemical controls or fungicides are unnecessary and if they are used, they are highly ineffective. Watering according to the 1-2-3-2-1 lawn watering technique will help prevent slime molds from developing. If slime molds do develop, they can be managed by waiting until the area is dry and then rake or mow the affected areas. Using a hose to wash the slime mold with a forceful stream of water is also an easy way to manage their presence.

Tree Leaf Damage

This lawn has a very strange spotted pattern to it and at first glance it looks as if it has some strange or exotic disease. What caused this discoloration has nothing to do with the lawn, instead it was caused by the tree. This tree had dropped a lot of leaves for the fall and the homeowner allowed the tree leaves to sit on the grass for 3 weeks without cleaning them up. The leaves blocked the sunlight from reaching the grass and all the brown spots are caused by a lack of sunlight. It is important to rake or mow the leaves that are sitting on the grass. This lawn will recover as soon as it gets adequate sunlight but it might take a few weeks for full recovery.
Damage from Tree Leaves

Preventing Lawn Diseases

Sound Cultural Practices are The Key to a Healthy Lawn!

The key to treating and preventing lawn fungus problems is as simple as creating an environment which stimulates a diverse populations of microorganisms, which is called a living soilWhen the soil is healthy the lawn’s ecosystem is in balance and the lawn will look great!

That being said all species of plants are subject to disease infestations. Fungi cause the majority of grass diseases. Turf grasses are susceptible to disease infestations because turf is a mono-culture comprised of a large number of similar species having a uniform genetic makeup. During stressful conditions like heat, drought stress and poor cultural practices a pathogen (disease or fungus) invades the turf grass. These problematic grass diseases become destructive and can spread quickly if the environmental conditions are prime for the fungus.

The most effective grass disease control in Colorado is to maintain proper lawn care cultural practices, such as proper lawn mowing techniques, the use of organic lawn fertilizersproper lawn watering (deep and infrequent watering), core aeration, and avoiding the use of all lawn chemicals.

Necrotic Ring Spot fungus

Necrotic Ring Spot is a common disease that affects lawns and grass worldwide. This lawn in Boulder Colorado was one of the worst cases of NRS and it took 2 years to repair this lawn.

How Does Organo-Lawn Control Lawn Diseases without using Chemicals?

If you didn’t notice that every lawn disease in Colorado is preventable by watering according to the 1-2-3-2-1 lawn watering technique.

Most lawn diseases are caused by improper cultural practices like poor irrigation management and mowing the lawn too short. If the lawn is suffering from a lawn fungus or disease, we will draw up a plan to first stop the cause with the lawn problem and then fix the lawn disease. Our permanent fix will usually involve making simple but important changes: such as adjusting mowing height and adjusting watering schedules. We never use fungicides to fix lawn problems because they usually cause more damage to the situation.

Before applying any fungicide to your lawn, call our offices today to schedule one of our professional lawn care technicians to come out to perform a disease diagnosis. We do charge for this lawn care service, but we waive all or some of the fee if you end up using our recommendations to correct the lawn care problem. Remember the first step in repairing a grass disease is properly diagnosing what is causing the problem to occur in the first place.

Organo-Lawn is your local lawn care expert and can explain in Layman’s terms what is causing the lawn to have brown spots. Call today to talk to one of our professional lawn care technicians. (303) 499-2000 Boulder or (970) 225-9425 Fort Collins

Lawn Care Expert

FAQ – Lawn Care Program

What is the most common lawn fungus found in lawns in Colorado?

The most common Colorado lawn fungus is called Necrotic Ring Spot. This lawn disease is a perennial soil borne lawn fungus that affects Kentucky bluegrass and is caused by severe over watering of the lawn for a long period of time. Ascochyta Leaf Blight is another lawn problem that affects lawns that have shallow digging grass roots

How to treat lawn diseases without using chemicals?

Following the 1-2-3-2-1 lawn watering recommendations is one of the most important steps to preventing and curing lawn diseases. Improper lawn watering practices are the main cause of 99% of lawn diseases. The most effective defense to pathogen infestations is to maintain proper lawn care cultural practices, such as proper lawn mowing techniques, the use of organic lawn fertilizers instead of chemical lawn fertilizers, proper lawn watering (deep and infrequent watering), core aeration, and avoiding the use of chemical pesticides at all times.

To schedule organic lawn care services please call our office at (303) 499-2000 Boulder or (970) 225-9425 Fort Collins.