Monitoring and targeting of a range of treatments are key to managing this notoriously difficult problem.

Fairy rings are a common problem on bowling greens. Although they can be seen throughout the year, they are at their worst during the warmer period from spring – autumn. Fairy rings compromise playing quality due to cover loss, surface subsidence, or the lush ring of growth that typically occurs around the edge of the ‘rings’.

Fairy rings are caused by several soil-inhabiting fungal species, which are collectively referred to as basidiomycete fungi. Cunningham (1934) mentioned that there were 6 fungi that caused fairy rings in New Zealand; 3 of them were common in greens and lawns while the other 3 caused rings in fairways and rough. Fairy rings can occur in a range of soil types but are generally worse on greens which are thatchy or constructed from light (sandy) soils. They are not confined to turf areas and are often seen on farms (especially in dry regions).

Typical fairy ring symptoms on a bowling green.

Damage symptoms due to insufficient moisture.

The causal fungi of fairy rings live saprophytically (i.e. live only on plant and organic matter) in the soil. It is the feeding on this organic matter that releases nitrogen and gives rise to the dark green, ring symptoms.

Fairy ring, unlike other diseases such as Brown patch or Sclerotinia spp, does not directly attack cotula or starweed plants. The results of the fungi activity, however, can affect them both. The damage seen or associated with fairy rings is largely due to:

• Dry patch i.e. the fungi causes the soil to become water repellent and plants die from moisture stress.
• Lush growth as a result of nitrogen being released by microbial activity within a ring.

The main signs and symptoms of fairy rings are:

1. Large (300mm to many metres in diameter), irregular-shaped, green rings forming primarily during spring – autumn. Note: during summer, the ‘ring’ can turn yellow then brown as the cotula or starweed suffers moisture stress before finally dying.
2. Mushrooms or puff balls (basidiocarps) developing within the ‘green ring’.
3. Plugs taken from a fairy ring typically have an orangey–tan brown discolouration within the thatch where the fungi are feeding, and a distinctive, musty or mushroom-like smell.

Orangey-tan coloured thatch zone where fairy ring is active.

Fruiting bodies (mushrooms).

Managing fairy rings

When managing these rings, it is important to understand that the fungus is found in the soil (and not in the plant which is more normal when dealing with disease). Consequently, the zone where the fungus is located in the soil profile must be targeted if long-term control is to be achieved.

The ‘active zone’ of the fairy ring (which must be targeted) is about 100-300mm beyond the ring and to the depth of any mycelium visible in the profile.

Soil moisture

When preventatively managing fairy rings, the first priority is to maintain adequate moisture within the ‘green ring’ (i.e. the active zone). Fairy rings produce a lot of mycelium and it is believed that this prevents water entering the soil, giving rise to dry patch-type symptoms later on in the summer.

White mycelium seen to depth. This whole zone needs to be treated.

Key requirements will include:

• During the spring – autumn period, monitor soil moisture levels by frequently using a core sampler or moisture meter. As the soil dries, parts of the ring will turn yellow, then orangey brown, before dying as moisture stress increases.
• Depending on your sampling, it is important that the ‘rings’ are regularly wetted up with hand watering. Automatic sprinklers alone are insufficient to maintain adequate soil moisture.
• Make sure the fairy rings and the active zone are fully wetted up to at least 150mm (or where the mycelium can be seen to) by the end of October.
• The use of a penetrant/wetting agent can help achieve infiltration into fairy rings. Typically, wetting agent programmes are more effective when the fairy rings are treated individually, i.e. the offending area is shallow spiked and the wetting agent drenched into the affected area. Continue hand watering for the next few days until the profile is adequately wetted up.

Once the cotula or starweed starts to change colour, dry patch is generally well established and a curative rewetting approach is required. This usually requires a combination of shallow spiking, applications of a penetrant wetting agent, then hand watering several times a day over 2–3 days until such time as the profile is fully re-wetted to depth.

Thatch management

A renovation programme that adequately dilutes thatch is an important requirement. It removes the food source (thatch) for fairy rings, while the intermixing of soil reduces the severity of subsidence from the microbes’ feeding activity.

Sugar

As long as the active zone is moist, applications of sugar (particularly during autumn) can reduce the severity/mask the symptoms of the rings. The sugar acts as a food source, enabling competing fungi and bacteria to multiply, providing a more balanced microbial population.

Care is required when using sugar as it can burn the cotula or starweed if not adequately washed in. Additionally, some fungi (specifically Sclerotinia and Rhizoctonia spp) are encouraged by the use of sugar.

Potassium carbonate

Potassium carbonate has proven successful in reducing the severity of fairy rings when it’s applied during spring. With its high pH and salt index however, it will burn the turf if not adequately washed in. Greenkeepers must take appropriate precautions when handling this product.

Best results are achieved where programmes start in early spring when the rings are first observed. A follow-up application is typically made a fortnight later.

Fungicides

Fungicides are notoriously ineffective when controlling fairy rings. The issue is that many of them are rapidly adsorbed on to the organic matter – before they can be washed deep enough into the profile to have an effect on the disease. Remember – the fungicide needs to target the fungus in the soil profile, not the plant.

Fungicides that are effective against or registered for controlling fairy ring are:

To minimise the effects of adsorption, the offending area should be ‘peppered’ with shallow holes, the profile saturated, then the fungicide drench applied and thoroughly washed in.

Chemical treatment can be carried out in either spring or autumn. To date, the most reliable and consistent control has been achieved when the rings have been treated at renovation, i.e. this allows the fungicide to get well into the soil profile.

Do the basics

To summarise, fairy ring is a common and notoriously difficult problem to control on bowling greens. Identifying the ‘active zone’ and providing adequate soil moisture levels should be the first priorities. It’s only then that the range of control strategies can be tried.

Reference

Cunningham,G.C. (1934), Control of Fairy Rings. Greens Research Committee, NZ Golf Association, 2^nd Annual Report pp 44-46

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