Common Lawn Diseases & How to Stop Them in Their Roots


Keeping a lush lawn or garden is one of the more satisfying things you can do with your free time. However, from time to time, it can turn into a frustrating ordeal.

You think you are doing everything right – mowing, watering, fertilizing – but all of a sudden, you start noticing unsightly yellow or brown patches or weird white dust-like substance. If you are really unlucky, these begin to spread – and you don’t have a clue what happened.

That’s just one of the scenarios when you find yourself face to face with lawn diseases.

What can we do to prevent and combat lawn disease?

In this article, I will teach you a few things about common lawn diseases. We will look at some of the trickiest and most dangerous turf grass diseases, the reasons for their occurrence, and what you can do to stop them. When you’re done with reading, you’ll be skilled in identifying lawn problems.

Identifying the disease is the key to defeating it, so pay special attention to the Lawn Disease Identification section.

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What is Turf Disease?

Just like when we talk about human or animal disease, lawn turf disease can also be caused by various pathogens. While bacteria and viruses are the most common causes of animal disease, fungus (molds) rank high on the pathogen list in the plant world, especially among turf grasses.

There are many species of fungus that can attack your lawn under right (or should I say wrong) conditions. All of them have a signature look, and later we will learn to identify them.

Another type of lawn “disease” is pest attack. While it may look like a disease, it is mechanical damage by insects or other critters that leads to growth irregularities and wilting.

pests and disease cause yellow spots to green lawn

Why Lawn Diseases Occur?

Turf diseases usually don’t strike at random. Fungi and their spores are everywhere and are a natural part of every lawn.

When all the biological factors are in balance, they don’t cause disease.

However, when something in the environment or within the plant itself is out of order, fungi can proliferate and become a problem.

Three main factors contribute to the actual manifestation of the disease.

Below the leading causes, I’ll list reasons for their presentation:

Weather conditions that favor the proliferation of the fungus

  • Cloudy or overcast weather for days.
  • Not enough direct sunlight.
  • Excessive moisture from rainfall, humidity, or improper watering.

Weak or feeble turf

  • Genetic reasons (bad stock).
  • Unfavorable climatic conditions for a particular grass species.
  • Adverse weather conditions in general (drought, soaking rains).

Aggressive or inadequate management practices

  • Low mowing.
  • Too frequent mowing and grooming.
  • Overwatering.
  • Overfertilizing.
  • Nutrient deficiency (under-fertilizing).
  • High traffic.
  • Dirty mowers.

Another reason why a classic lawn is vulnerable to plant diseases is that it is a monoculture.

That means that a typical lawn consists of one grass species only. When a pathogen becomes adapted to a particular grass species, it can quickly spread to all neighboring plants with no barrier.

It wasn’t always like that. In the old days – 19th and early 20th century – lawn seeds were sold as mixes rather than seeds of a single species.

Relative severity of selected diseases on five cool-season turf species.

Turfgrass Disease Profiles
Source: www.extension.purdue.edu

— = rare; no symptoms, not susceptible.
+ = sporadic; damage is mostly cosmetic and has a short duration.
++ = sporadic; cosmetic damage is of major concern, and structural injury will lead to thin, poor quality turf.
+++ = sporadic; cosmetic damage and serious structural injury to turf depending on the extent and duration of the outbreak.
++++ = chronic; potential for severe structural injury that will affect appearance and playability for unacceptable periods.

Lawn Disease Identification

Let’s look at some of the most dangerous, treatment-resistant, but also most common lawn diseases.

The type of infection you can expect to appear on the lawn depends on the climate, current weather, and the time of the year.

As you will see with each disease, management (also called cultural) practices can either increase or decrease disease susceptibility.

Pythium Blight and Other Pythium Turf Diseases

Pythium Blight Turf
Source: https://ag.umass.edu/turf/fact-sheets/pythium-diseases-of-turf

Pythium is a genus of fungi that causes various diseases in turfgrasses and other plants. Pythium blight of turfgrass is the best known of all of them, infamous for its quick spread, high mortality of affected plants, and extensive turf loss.

If you don’t try to stop the disease and the weather conditions don’t become less favorable for Pythium spread, large turf areas can completely die off in only a few days.

At the onset of the disease, you will notice relatively small round patches of water-soaked, dark, “greased” grass in short-mown turfs. During dew hours early in the morning, you may also see cottony white mycelium. When turf dies, it becomes matted.

Cause of Pythium Blight on Lawns

The disease is of fungal origin, with Pythium fungi being the cause. Although several Pythium species can cause blight, Pythium aphanidermatum is most commonly to blame.

However, weather plays a vital role in the spread of the disease. Pythium aphanidermatum outbreaks occur during summer days with long dew periods (lasting 14 hours or more), late afternoon rains, and evening temperatures are at least 68°F.

They are most common in low areas where dew forms early in the evening and remains until the morning.

Unlike some other diseases which thrive in low-fertility soils, Pythium loves to attack lush turfs with high or excessive nitrogen in the ground.

Affected Grass Species

  • Creeping bentgrass (particularly affected)
  • Rough bluegrass (particularly affected)
  • Annual bluegrass (particularly affected)
  • Perennial ryegrass (particularly affected)
  • Kentucky bluegrass (limited damage)
  • Tall fescue (limited damage)

How To Fight Pythium Blight

Applying fungicides to fight Pythium is tricky and is best left to professionals. The fungicides efficient against Pythium are used in recommended tank mixes.

They must be rotated among Further Resistance Management Recommendations for Modes of Action (FRAC) groups because it’s the only way to prevent fungicide resistance development.

Management Practices to Fight Pythium Blight

  • Preventing water logging is the key; Improve drainage, avoid overwatering, do not water in the late afternoon or evening, reduce automatic surface watering and use syringing.
  • Avoid overfertilizing, especially with nitrogen. Use slow-release nitrogen fertilizers instead of quick-release fertilizers.
  • Ensure adequate calcium levels can also increase susceptibility to Pythium blight.
  • Mechanically remove thatch (when it exceeds 0.5″).
  • Adjust mowing practices: raise mowing height, reduce mowing frequency, don’t mow wet grass, and especially if you can see the mycelium (cottony structures).
  • Plant Pythium-hardy grass cultivars.

Dollar Spot Disease in Grass

Dollar Spot Disease in Grass
Source: https://ag.umass.edu/turf/fact-sheets/dollar-spot

Dollar spot is a fungal turf disease that got its name from its beginning manifestation – straw-colored or whitish circles the size of a silver dollar, 1-3 inches in diameter.

In time, they can spread to be 6 inches wide. In severe cases, circles will merge, forming large irregularly-shaped blocks of affected grass, usually sunken.

On humid nights or in the dew-rich mornings when the fungus is active, you may be able to notice cotton-like or cobweb-like growth too.

When you look at the grass blades, you will see small white-to-straw-colored patches, often with brown or reddish-brown hourglass-shaped margins.

Cause of Dollar Spot Disease on Lawns

The pathogen behind the dollar spot disease is the fungus Clarireedia jacksonii, although, in literature, you will also find it under its former name, Sclerotinia homoeocarpa.

It is active from May to October and appearing in temperatures ranging from 60 to 90°F. It prefers the weather pattern with warm days, cool nights, and heavy dew.

Beyond weather, C. jacksonii also prefers a particular type of soil. It gets most severe in dry soils with low nitrogen. Also, it stays dormant and survives unfavorable periods in the thatch, so having a thatch-filled lawn is also a contributing factor to the fungus survival and proliferation.

The fungus can be spread by mowers, golf carts, shoes, and by wind and water. Because of that, and because of frequent chemical treatments, golf courses are especially susceptible.

Affected Species of Grass

  • Fine fescue
  • Tall fescue
  • Perennial ryegrass
  • Bentgrass
  • Centipede grass
  • Kentucky bluegrass
  • Bermudagrass
  • Zoysa Grass

How to Combat Dollar Spot Disease

The dollar spot disease is notoriously fungicide-resistant, especially in the case of frequent and heavy treatments of the lawn.

Unfortunately, if you want to rely on fungicide treatment as a sole way of controlling the disease, you are in for a lot of work with an uncertain result.

Preventive treatments during the favorable season, changing and using fungicide of different fungicide classes, and avoiding fungicide that the C. jacksonii has the most resistance to are some basic instructions. However, you may benefit from professional advice.

Everyone agrees that using cultural practices that sabotage the fungus, with or without chemical management, is the central pillar of fighting dollar spot disease.

  • Water stress: watering should be deep but infrequent, and not often, and superficial. Also, you can remove dew in the morning by rolling, whipping, or poling the grass early in the morning. You can also mow, but mowing wet lawns is not recommended.
  • Apply nitrogen fertilizers frequently per instructions to avoid nitrogen depletion.
  • Use organic fertilizers such as compost and bio fungicides.
  • Overseed with newer grass cultivars which were selected to be not so susceptible to the disease.
  • Consider using mixed-species lawn seed mixes that include low flowering species such as white clover; clovers will also help maintain adequate nitrogen levels.

Anthracnose Lawn Disease in Grass

Anthracnose Lawn Disease
Source: https://content.ces.ncsu.edu/anthracnose-in-turf

Anthracnose is a fungal disease that appears in two forms:

  • Foliar Blight
  • Basal Root

Foliar blight symptoms look like yellow and brown, irregular patches on turf at the beginning. Soon, the patches turn tan, and the grass dies.

A look under the magnifying glass can reveal black, hair-like structures representing the fungus’ flowering. It can look similar to extreme drought stress, but the main difference is that the symptoms are made worse instead of less severe with watering.

Basal root symptoms include yellowing of the leaves, the brick red color of the youngest blades, and black root at the blades’ base. When the fungus infects the growing part of the plant, the recovery is slow and uncertain.

Cause of Anthracnose Disease on Lawns

Anthracnose is caused by the fungus called Colletotrichum cereale. The disease has become much more aggressive in recent years in places of intensive turf management such as golf courses.

Anthracnose lives and survives in plant debris, living as a saprophyte – an organism that feeds on dead matter.

However, when the grass is stressed from heat, low mowing, poor drainage, heavy foot traffic, too much thatch, and nutrient deficiency, the fungus can turn on the living plants.

Affected Species of Grass

  • Annual bluegrass (particularly affected)
  • Kentucky bluegrass
  • Creeping bentgrass
  • Fine-leaf fescues
  • Bermudagrass
  • Perennial ryegrass
  • Meadow grass

The disease commonly strikes at golf courses.

How to Combat Anthracnose Lawn Disease

As with the dollar spot disease, Anthracnose is hard to treat with fungicides. It responds better to preventive treatments rather than curative ones.

If the treatment is needed and unavoidable, it is best to get anthracnose while it is in its foliar stage.

The weapon of choice is a multi-site fungicide protectant such as chlorothalonil, plus a systemic penetrant fungicide.

As with other hard-to-treat diseases, it is much better to try to work on anthracnose prevention via good lawn management practices.

  • Avoid low mowing, especially during periods of disease outbreaks and heat stress. Increasing mowing height just 0.1” can already help lessen the disease severity.
  • Do proper essential maintenance – aerate and dethatch.
  • Improve drainage and air movement (by pruning trees and bushes where needed).
  • Make sure that nitrogen and potassium levels are sufficient.
  • Be mindful of irrigation because both underwatering and underwatering can help the disease spread.
  • Whip the dew, especially when the humidity is high for days on end (this is beneficial for all fungal lawn diseases).
  • Consider syringing the turf during high heats.
  • Conduct spring and summer topdressing.
  • Wash the mower well after using it on the diseased areas.

Bacterial Diseases of Turfgrass

Here’s something to add to the variety. Besides fungal diseases, turfgrass can also be affected by harmful bacteria.

While similar in appearance, there is one major difference between bacterial and fungal diseases. While fungi can attack otherwise healthy turf if the weather conditions are right, turf bacterial infections occur almost exclusively due to stress and aggressive management practices.

Causes of Lawn Bacterial Disease

Bacteria called Xanthomonas translucens pv. poae causes bacterial wilt in annual bluegrass, while Acidovorax avenae subsp. avenae causes paleness and a general decline in bentgrass.

Because the causes and the symptoms are similar, the two diseases are often described as one. Also, other diseases can occur along with bacterial infection.

The first symptoms are small, yellow spots; soo, thinning of turf begins to show, especially in high-traffic areas. Another characteristic symptom is etiolation – pale-yellowing and elongation of the leaves as if the plant was growing without sunlight. Collapse and death may also occur.

As for the weather conditions, bacterial turf decline usually occurs in high humidity when daytime temperatures are in mid-80s F.

The bacterial turf diseases develop in places of high turf stress – intense grooming, heat and drought, low nitrogen levels, and increased traffic.

Another significant factor is mowing. Mowers can transmit bacteria between different lawn segments, and mowing cuts on the leaves serve as an entry point for the microorganisms.

That is how contaminated mowers can disseminate the disease. Low mowing also contributes to the general susceptibility of the lawn to stress and diseases.

How to Fight Bacterial Wilt

Unfortunately, conventional bacteria-killing treatments don’t exist for this disease. The most you can do in chemical management is to use plant growth regulators (PGRs).

However, it is sort of a gamble because PGRs can make the situation better or worse. The effects depend on many factors such as the active ingredient in question, concentration, and environmental conditions.

On the other hand, management practices can do no damage. Here’s what to do to curb the spread of turf bacteriosis.

  • Mow the lawn only when it’s dry. Wet mowing creates bigger wounds on the blades, and these are ideal for microbes to enter.
  • Increase mowing height and reduce the frequency.
  • Avoid grooming, aeration, and topdressing the lawn when the disease is active.
  • Avoid fertilizers with ammonium sulfate, which can exacerbate etiolation.
  • Don’t walk over the affected areas.
  • If possible, use a different mower for the diseased patches; alternatively, carefully wash and disinfect your standard mower.

Other Lawn Diseases (and What to do About Them)

bare yellow spots in grass

The lawn disease list is really long (and many of them have pretty vivid names). I’ll just name a few: Fairy Ring, Powdery Mildew, Slime Mold, Gray Snow Mold, Pink Snow Mold, Brown Patch, Take All Patch, Summer Patch, Necrotic Ring Spot, and so on.

Although the exact treatment for each may vary, there are several steps that work in stopping all lawn diseases.

If you analyze the previously mentioned management practices, you could draw out the conclusion yourself, but here is the “best-of” list for your convenience.

  • Try to reduce moisture on your lawn; avoid frequent and shallow watering, as well as overhead watering in humid periods of the year (use syringing instead). Whipping, rolling, or poling and can help reduce dew in the morning.
  • Mow as high as practical, and avoid mowing wet lawn.
  • Aerate and dethatch the lawn regularly.
  • Avoid overfertilizing and under-fertilizing turf and make sure it has optimal nutrients.
  • Overseed with disease-resistant cultivars, or opt for an ‘alternative,’ mixed-species lawn.
  • If disease occurs, use only approved fungicidal treatments strictly per instruction; use a different mower for the affected area.
  • Wash your mower diligently, especially if the part of your lawn is affected, as mowers are great disease disseminators.

Conclusion

While different pathogens prefer different hosts (grass species) and variable climatic conditions, the golden rule with all lawn diseases is that prevention is better than the cure.

Using best management practices is the most efficient way to prevent lawn disease.

If the disease does occur, make sure that chemical treatments are also according to the best available techniques, and make sure to get it fast – diseases like Pythium blight can kill a large chunk of your lawn in only a few days.

Do you have any problems with lawn diseases? What was the worst one to strike your turf? How do you manage? Help others by sharing your precious experience in the comments.

Andy Gibson

My name's Gibson. Andy Gibson. I like to think of myself as the Bond of the backyard, that is if yard work ever became sexy. I write about everything about indoor and outdoor gardening and the dread-it-but-still-need-to-do-it chores around the yard, like cleaning out the gutter guards.

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