Fairy Rings Lawn Disease - Identification, Cause, Symptoms and Treatment

A Fairy Ring is a lawn disease that is caused by certain types of fungus that causes a ring-like shape on the lawn.

What does a fairy ring look like?

The effect and appearance of a fairy ring can vary depending on what type of fungus is causing the problem. They generally form one or more of the following:

A ring of toadstools on the lawn when there is enough moisture
One or more rings of deep green, lush looking grass
Areas of dead / yellowed grass or bare soil between the lush rings.

The following image shows a ring of toadstools on the lawn that are visible above ground. These are the result of the fungal threads below ground.

Image credit: Famartin / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Some may find a fairy ring that of the toadstool type an attractive feature. Especially in a grassy woodland environment.

They can, however, cause serious problems on a more formal lawn.

Dead grass, uneven colour, bare patches, and toadstools are all undesirable features for a formal lawn.

What causes fairy rings in lawns?

Fairy rings are the result of certain types of fungi forming fungal threads in the soil that the turf is laid on.

The most common fungus to cause fairy rings is Marasmius Oreades. The threads that form are very densely packed, often reaching down so soil depths of around 20cm. They have been known to reach down to about 40cm.

The effect of the tightly packed threads on the grass is to starve the roots of both water and nutrients. They do this by inhibiting root growth and preventing water uptake.

The resulting lack of water will effectively kill the grass in badly affected areas of the lawn. This results in yellow/brown patches of grass appearing around the fairy ring.

Bare patches of soil may appear on the lawn where the grass has been dead a long time.

Photo © Alan Hawkes (cc-by-sa/2.0)

Mycorrhizal fungi live in a symbiotic relationship with trees. These fungi attach to the tree’s roots and form what is sometimes known as a “tethered” ring.

The fungi relies on its interaction with the tree roots. It is therefore prevented from moving too far away from the roots so is “tethered” to the tree.

Totodu74 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

What causes the fairy ring to be a ring and not a circle?

The fungal threads grow outwards from the centre. When the older threads in the centre grow older and die they are broken down by the soil microorganisms. This releases nutrients back into the soil. The grass is then able to re-grow and thus the centre of the circle returns back to ‘unaffected’ lawn.

The reason for the dark green grass is that the threads produce chemicals (termed ‘fairy chemicals’). These are released into the soil on the outer edge of the fairy ring. These chemicals release nutrients in the soil. They can also regulate plant growth. This can give a temporary effect of the grass being lusher due to the extra nutrients that are available to it.

This effect is only temporary however. The threads then expand into this soil on the outer edge of the ring and start to have their detrimental effect on the grass roots.

The following image shows 2 fairy rings where no toadstools are visible. The effect of the fairy ring here is a ring of darker shaded grass.

There is a small, well-defined ring at the front of the photo. A larger, less obvious ring that spans the whole width in the top half of the photo.

How large and quickly can a fairy ring grow?

This can depend on climate, mushroom type and ground conditions. An annual growth rate of around 20cm is possible if there are no barriers to growth.

Field mushrooms (Agaricus campestris) commonly give rise to fairy rings of around 2m in diameter. Marasmius oreades can reach diameters of over 365m but maybe more irregular in shape¹.

There are instances where they can grow much larger than that² although this tends not be in lawns.

According to Utah State University fairy rings can grow

Treatment of Fairy Ring in your lawn

Prevent spreading by removing spore producing toadstools

Once a fairy ring has established itself on your lawn it can be very hard to remove. To try and prevent the spreading of the fairy ring you can cut any of the toadstools off at their base. Place them in a container.

Once you have collected all the toadstools burn them. Do not put them on the compost heap or redistribute them over the lawn or soil. This is because they contain spores that will further the growth of the fungi. Burning the toadstools will destroy the spores.

Prevent spreading by mowing separately

Another tip for preventing the spread of a fairy ring is to mow the infected area independently. This means collecting the grass clippings separately and burning them. Do not add the clipping to the compost heap as they can contain the fungal spores.

After mowing the infected section of the lawn, use a fungicide to clean down the mower. This will kill any fungal spores on the mower that could get transferred to a healthy section of the lawn.

Help the grass by aerating and watering

Another treatment for fairy rings is to to make aeration holes in the turf that follows the ring. Use a garden fork to make the holes and penetrate into the soil below.

This will increase airflow into the soil and improve the ability of water to penetrate into the soil. The roots of the grass are then better able to access water.

After forking the soil you can then water around the ring to provide the affected grass with the water it needs.

Remember to clean your fork thoroughly afterwards. This will ensure that you don’t spread any fungal spores.

How do I get rid of a fairy ring in my lawn?

Getting rid of fairy rings can be tricky but worthwhile. If you don’t take action then the fairy ring can continue to grow for a number of years.

Get rid of fairy rings with fungicide

You may be able to use a fungicide containing dichlorophen that is suited for applying to lawns.

Make sure to check with the manufacturer’s instructions for application and usage guidelines. You don’t want to kill off all flora and fauna!

How to dig out a fairy ring

One labour intensive way to restore your lawn is to literally replace the infected part of the lawn.

Place a plastic sheet/tarpaulin over the lawn next to the fairy ring.
Dig up the turf from the centre of the fairy ring to 18 inches outside the infected area. Place the turf on the plastic sheet so it does not infect the rest of your lawn.
Once the turf has been removed, dig up the infected soil that contains the fungal threads to a spades depth.
Discard this soil (not on the lawn and preferably at a waste disposal site).
Fill the area with fresh uninfected top soil. Mix some well rotted compost or manure into this new soil as according to an article in the Nature journal from as far back as 1884 fairy rings are: “rarely developed on rich soils, or on those which are highly manured”… “They prevail wherever the growth of the grasses is inferior, especially on the poor downs of the chalk districts, and on poor sandy soils where the natural herbage is wanting in vigour.”
Re-sow with lawn seed or lay new turf on the now bare area of lawn.

Why are they called fairy rings?

According to folklore the pattern of toadstools in the ring are the result of fairies dancing around a ring.

References

Fairy Rings Lawn Disease – Identification, Cause, Symptoms and Treatment