Looking out across a vibrantly green, healthy lawn is a sight to behold. Millions of individual plants take root and create a veritable sea of green that begs to be walked barefoot. Proper care and maintenance can keep a yard looking luscious and green. However, sometimes when you think you are doing everything right, you look out across that sea of green and see brown patches, rings, or spots. Many people see these spots and assume their watering is lacking in areas and double down to try to make sure their grass gets an increase in watering only to find these sickly-looking areas of their lawn are getting worse instead of better. That is typically because the turf is diseased, not necessarily lacking water.
Fungal Diseases are by far the #1 Problem
A fungal infection of some sort causes most lawn diseases. Most fungi thrive in warm and moist conditions, and the biggest culprit for many fungal diseases of turf is from over-irrigation or inadequate drainage. Fungal infections can be mitigated by altering the conditions in which the fungus thrives. Smarter irrigation and drainage can often solve fungal problems with lawns. Many of these diseases also react to the amount of nitrogen in the soil. Some fungi will flourish with applications of slow-release nitrogen fertilizer. Others will completely disappear. In other cases, when a fungus has established itself into the soil or surrounding foliage, the best way of treating it is to hire a professional lawn care company. Lawn care professionals are trained to identify specific types of fungi that are threatening your turf. Antifungal treatments are applied regularly to abate the growth of the organism and eliminate conditions in which they tend to reproduce. Homeowners and property owners also want their lawn to be on the proper nitrogen fertilizer regimen to squash unwanted fungal growth. While some of these fungal infections can take several treatments to eliminate, many can be eradicated early through proper identification and treatment by a qualified lawn care professional.
Bacterial and Viral Diseases
Although it is uncommon, turf can also suffer from bacterial and viral diseases. Not all bacteria are harmful, and in most cases is a good thing to help keep the ecosystem of your turf in balance. However, occasionally, bacterial infections can occur in plants. The most common symptom of a bacterial infection in your turf is the spotting of leaves, stems, or fruits. Sometimes, bacteria can cause a soft rot of your grass, which can then give your lawn a slimy appearance. Viral infections of turfgrass can also cause many of the same symptoms as fungal or bacterial infections. Often there is no treatment for viral infections in plants other than prevention.
Common Lawn Diseases
Note that a fungus causes all of the lawn diseases listed below except for Pythium blight and Pythium root rot. Pythium was previously classified as a fungus, but the scientific community now classifies it as a fungal-like microorganism called parasitic oomycotes.
Dollar Spot – Aptly named for the silver-dollar-sized spots it leaves in your lawn, dollar spot is caused by the fungus Sclerotinia homoeocarpa. It produces spots that are yellowish-green to straw-colored in yards and gives a lawn the appearance of freckles. Most spots in grass that is cut short are only around 1-3 inches in diameter. However, in lawns where the grass is cut higher, spots can range between 2-4 inches in size. This fungus used to only be prevalent on golf courses, but can now be found anywhere it’s tracked. The fungus spreads through the mycelium, which is usually white-colored, thready part of fungi that is visible. Thus, it can spread to areas of healthy turf through grass clippings, wind, or even by being tracked by your shoes. It is most common in areas where there is high humidity, or irrigation heads are spaced too closely together as a result of holding onto too much moisture.
Brown Patch – Brown patch is a serious fungal disease that can leave large dead-looking patches in your turf. It is caused by the Rhizoctonia solani fungus and can develop any time during the growing season when temperatures remain relatively warm and humid overnight, and there is an extended period of grass wetness. This fungus usually creates thinning patches of grass that are light brown and in a somewhat circular shape. The center of the patch can often recover, leaving a doughnut-shaped pattern. This fungus is one of the most significant contributors of disease in almost all types of grass, though it is prevalent in tall fescue. The disease is spread through resting bodies called sclerotia within infected grass tissue or within the soil itself. It can remain in the soil for many years even in the absence of turf and reinfect newly laid or planted turf years down the road if left untreated.
Red Thread – Laetisaria fuciformis is the fungus responsible for this type of turf disease. Red thread is named for the reddish cast it gives to areas of blighted grass that appears in irregularly shaped patches. The disease is typically restricted to only the green parts of the grass plant, but in severe cases, it can kill the entire organism. It is usually identified in late stages of infection when grass produces a bright pink-colored mycelium at the tips. It is spread to areas of healthy turf through the mycelium by either the spread of yard clippings or walking through affected areas. The fungus is easily spread through the tips of other blades of grass and is most common immediately after periods of intense, heavy rain or excessive humidity.
Rust – Several different rust diseases can infect healthy turf, and the fungus Puccinia spp causes them. Early on, blades of grass may appear to have some light yellow spotting or flecking along the leaves. As the disease progresses, these spots turn into a deep reddish-orange pustule which then can rupture and send thousands of tiny spores into the immediate area. The disease gives off the appearance of rust, and walking through or rubbing your fingers on infected areas can release a very fine, red dust. This disease generally occurs only in late summer and early autumn and does not typically occur during other times of the year. While rust diseases don’t usually kill turf, they can weaken or stress your lawn, making it more susceptible to weeds or other diseases.
Leaf Spot – Leaf spot is caused by the Bipolaris fungus, and is extremely prevalent among Kentucky bluegrass. In many cases, these organisms cause leaf spots that do little to harm the overall health and beauty of your turf. However, once cutting height is lowered, and nitrogen fertilizer is applied, some leaf spot diseases can have the capacity to kill your grass completely. When the leaf spot invades the entire plant from crown to root, it is referred to as melting out. Leaf spot can be troublesome because the fungal spores reside in dormant grass and soil and become activated in the cool, wet weather of spring. Spores are produced on the blades of grass and rain splashes the spores onto surrounding newly emerging blades causing the spread of the disease. Continuing generations of spores are produced in mid to late spring, which wash to the crown and root areas, causing the melting out of the entire plant.
Pythium Blight/Pythium Root Rot – Caused by the Pythium anaphanidermatum organism, Pythium Blight and Pythium root rot are among some of the fastest moving and catastrophic turf diseases. This fungus has the ability to completely blight a healthy turf within a period of just a few days. It first appears as small, irregularly shaped spots in grass and leaves appear to be water-soaked. Groups of spots often join together in a streaking pattern and are often determined by the flow and pattern of surface water. Grass may appear to be covered in a white, cobweb-like substance. This fungus can survive for long periods in soil and can spread through previously-infected plant debris or through spores.
Slime Mold – Caused by Mucilago, Physarum, and Fuligo spp., slime molds are a bit different from other turf diseases in that they do not infect turf. Instead, they feed on microorganisms and other decaying organic matter in soil and turf. When weather is warm and wet, slime molds make their way to the surface of their grass and begin producing reproductive structures, which is what gives the fungus a white, blue, or gray appearance. These fungi can survive weather conditions during its spore stage. When two spores unite, it creates a substance called plasmodium, which is when it takes on a slimy appearance. While these fungi may cause yellowing of grass in areas of disease as a result of shade, but very seldom actually severely damage turf.
Fairy Rings – Various mushroom spores cause fairy rings. They can either appear in yards as rings of richly green and fast-growing grass or the complete opposite–rings of thinning yellow and slow-growing grass. The rings can range in size from anywhere between a couple feet to a couple of hundred feet across and may contain a center of weakened or dead grass. The first signs of a fairy ring are often a crop of mushrooms or toadstools just outside the rings and typically crop up in late summer or early fall during periods of intense moisture. They are spread through colonies of mushroom fungi that can live in soil or thatch and continue to grow outward year after year. They don’t generally cause serious harm to grass, though in some cases they can repel water which can cause drought conditions in your yard and lead to the death of turf.
Spring Dead Spot – This type of fungal infection is most common in the Southeastern United States and is caused by Ophiosphaerella korrae. It can cause catastrophic damage to Bermuda grass and are most prevalent during cooler and wetter months of the year. Though the fungus does not usually kill the grass directly, it weakens it to make it more susceptible to damage from cooler temperatures. It can most easily be seen when turf greens up in the spring in healthy areas leaving large, round patches of dead grass. If not properly dealt with, patches will continue to get larger with each successive growing season. The fungus is generally spread mechanically by cutting, tools, and walking through infected areas to non-infected areas, and recovery from this disease is usually very slow.
Summer Patch – Magnaporthe poae is the culprit behind this disease that infects Kentucky bluegrass and fine fescue. This fungal infection presents in the same way as necrotic ring spot and needs to be analyzed by a professional if diagnosing the exact fungus is necessary. This disease causes rings of blighted grass throughout areas of your lawn, creating doughnut-shaped circular patches that can be as large as 12 inches in diameter. It colonizes in roots of the grass, and when conditions are favorable for this fungus, it will begin invading roots of healthy turf. It generally appears in mid-summer when temperatures are high for many consecutive days, and there is a lot of moisture–either through irrigation or rainfall.
Powdery Mildew – Erysiphe graminis can give blades of grass a powdery white appearance. In some cases, entire stands of grass can be covered in powdery mildew giving areas of your lawn a whitish-gray appearance as opposed to deep green. It infects healthy turf through spores that are carried by the wind and thrives in areas where there is poor circulation, high atmospheric humidity (but no moisture on the surface of grass), low light, and cooler temperatures. Kentucky bluegrass that is grown in shadier areas is particularly susceptible to powdery mildew infection.
Large Patch – This disease is caused by a different strain of the same fungus as brown patch. Infection can occur at any time during the growing season but are most common when grass is entering or leaving dormancy. It results in the formation of large patches of dead turf, as the name suggests, that can exceed 20 feet in diameter and is more severe in turf that is mowed to less than 1 inch. Large patch is spread the same way as brown patch through sclerotia within infected grass tissue or soil and can remain in the soil for years.
Treat is Yourself or Hire a Pro
If you believe you are dealing with a lawn disease, homeowners do have the option to purchase a lawn disease control product from a hardware store, or they can hire a lawn service to solve the problem. Hardware stores sell products that can attach to a hose and can be used to spray a whole lawn easily. These products are effective against some fungal problems but not all. Professional lawn care services, especially services that focus on lawn fertilization and weed control, are usually experts at treating lawn diseases. They have access to antifungal lawn treatments and other lawn applications that only licensed professionals can get.