0 Daily dose of Disease: Marasmius oreades (fairy Rings)

Daily dose of Disease: Marasmius oreades (Fairy Rings)

By Laurence Gale MSc

Diseases:

Diseases caused by pathogens (fungi, bacteria, viruses and nematodes) are the most numerous and infectious agents of plant diseases. The first step is to decide whether the problem is a plant disease. The definition of plant disease includes anything that adversely affects plant health. This definition can include such factors as nutrient deficiencies, mower damage, air pollution, and pathogens. Symptoms and signs are used to diagnose the condition of a plant. Symptoms are the physical characteristics of disease expressed by the plant. Symptoms can include wilt, galls, cankers, rots, necrosis, chlorosis, and general decline. Other signs of disease presence can include fungal fruiting bodies (such as mushrooms), mycelia, bacterial slime, presence of nematodes or insects, or the presence of insect holes.

Once you have determined that a real problem exists and is caused by a living organism, you need to decide what type of organism may be causing the damage. Begin by establishing which plant part or growth stage is showing symptoms. Are symptoms showing on roots, tubers, bulbs, corms, seedling, foliage, stem, branches, trunks, flowers, fruit, or on the entire plant?

Diseases can affect many parts of the plant: root symptoms include galls, discoloration, or death to parts of roots; death of the entire root system or just feeder roots is indicative of many fungi diseases. Injury to the root system often includes yellowing, stunting, or wilting of above ground parts (leaves and shoots). Seedling diseases, where the seedlings fail to emerge or die off, is referred to as damping off disease. Fungi such as Rhizoctonia, Pythium, and Fusarium are common and affect seedlings just at or below the soil line. Plants with white mouldy growth are diagnosed as having powdery mildew or downy mildew fungi.P-and-DDisease-triangle.jpg

Leaf symptoms are seen in many forms: discolouration (yellowing or shades of green), localised or in distinct patterns, usually indicates a virus; dead areas on leaves can be caused by fungi or bacteria. Necrotic areas caused by fungi may contain hyphae or fruiting bodies, particularly after incubation in a warm, moist environment. Understanding the specific disease or the life cycle of the pathogen involved is necessary to ensure effective controls can be implemented. Three major factors contribute to the development of a plant disease: a susceptible host, a virulent pathogen, and a favourable environment. (the disease triangle) A plant disease results when these three factors occur simultaneously If one or more of these factors do not occur, then the disease does not occur. The genetic makeup of the host plant determines its susceptibility to disease. This susceptibility or resistance may be determined by various physical and biochemical factors. Plant stature, growth habit, cuticle thickness, and stomatal shape are a few physical factors that influence disease development. The plant's developmental stage also may influence disease development. Pathogens differ in their ability to survive, spread, and reproduce. Environmental extremes of temperature, light, or moisture can accentuate many diseases. Cool, moist conditions are ideal for many fungal pathogens.

Understanding the disease cycle is important when considering control options. Learning the chain of events that contribute to a disease helps point out the weakest links. Control measures can then be used to break the cycle. Most pathogens must survive an adverse period, usually winter, when they do not actively incite plant diseases.

Disease Cycle:

The Pathogens that cause these diseases are always around and often laying dormant in the thatch layers waiting for the ideal conditions to become active. Once these spores are activated and have found an acceptable host they are able to grow and reproduce themselves, spreading new spores and infections to other areas of turf. This cycle continues whilst the right conditions prevail.

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Spores are spread by wind, water, and by traffic. It is during periods of fluctuating weather, particularly changes in temperatures, that an outbreak of disease takes place. Attacks can appear at any time of the year.

Disease : Marasmius oreades (Fairy Rings)

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Diseases generally become more prolific when the right conditions prevail. Late August - October are prime times for diseases to show themselves mainly due to the high levels of moisture found at the turf surface when dews are formed both in the mornings and evenings. It is this time of the year when you can expect to find toadstools and mushrooms growing in your turf areas.

Fairy rings are caused by many different soil-inhabiting fungi of the class Basidiomycetes. These fungi can cause the development of rings or arcs of deep green grass and bare dead grass areas.

There are three types of fairy rings:

Type 1 fairy rings (Marasmius oreades)

Type 2 fairy ring (Agaricusspp. and Lycoperdon spp.)

Type 3 fairy ring (Hygrophorus spp and Psilocybe spp.)

Type 1 is the most virulent.

Scientific name

Family

Marasmius oreades

Class: Basidiomycetes

Life cycle

The disease is caused by any one of a number of soil-inhabiting fungi. The early stages of development starts when germinating spores or a strand of mycelium begins to grow in the soil. The active fungi feed on accumulated organic matter found in the sward. These fungi strands (mycelium) can spread to depths of 300mm in the soil profile. The first visible evidence of a fairy ring is when a cluster of mushrooms or a darker ring of grass growth appears in the sward. These fungi tend to spread outwards forming a circular pattern in the sward.

The activity of the fungi in the soil initiate a break down of organic matter, resulting in the release of nitrogen into the soil which in turn stimulates grass growth, which is why you see dark green bands of grass growing in the affected areas. Also a ring of brown or dead grass may also develop, caused by the depletion of soil moisture in the area where the fungus is concentrated. This dense matt of mycelial growth prevents water infiltrating into the soil profile.

This mycelium becomes active during periods of moderate, wet weather, and the ring continues to grow outward each year.

Once established, fungi will remain in the soil profile for many years, often remaining dormant until the right conditions prevail to stimulate growth again. Unless treated or removed completely these fairy rings will continue to appear in the sward for many years.

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Form / Appearance

The growth pattern of Marasmius oreades nearly always grows in a circular pattern, commonly called a fairy ring. However, symptoms can also be seen as dark green patches of grass with associated bare areas. Tan-coloured fruits (toadstools) are often found in the rings and patches during the summer and autumn periods.

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Reproductive method

The fungi produces fruiting bodies that form on the turf surface, usually seen in the form of mushrooms (toadstools). These fruiting bodies grow and mature until they reach a stage when they break down, releasing thousands of spores, which are dispersed by wind, rain and surface water. These spores can remain in the ground for a number of years until the appropriate conditions prevail for re-emergence of new mycelium, beginning the disease cycle again.

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Habitat

Fairy rings are considered a turfgrass disease that can be very destructive to lawns, golf courses, parks and football pitches. Fairy rings develop most frequently in soils containing high contents of organic matter, or swards with thick layers of undecomposed thatch.

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Cultural Control

The best control method is to ensure that your sward remains healthy, encouraging the turf plant to produce strong leaf and root growth enabling the plant to withstand disease attacks.

Correct maintenance of grass cutting machines is vital. Badly adjusted and blunt cutting blades will result in unnecessary tissue damage to the grass plant, thus enabling the opportunity for disease to enter the grass plant through these wounds.

Masking the symptoms of fairy rings is most effective. Aerating and drenching the soil with a wetting agent will help prevent the development of dead and dry patches. Keeping the fertility level of the turf high will also help to mask the appearance of the ring of stimulated or dark green growth. Also, regular mowing removes the mushrooms and other symptoms of the fairy ring.

A programme of aeration and scarification is recommended to enhance the removal of thatch and organic matter from the soil profile, thus reducing the environment that stimulates fungi activity.

Removing the affected area is another method that can be used to control fairy rings, Digging out the affected areas and replacing with new soil and turf. However, this could involve removing large amounts of soil as it is necessary to ensure all affected soil is removed and discarded.

The disease triangle is a concept of plant pathology and is based on the principle that disease is the result of an interaction between a host, a potential pathogen and the environment or weather conditions. Plant disease is prevented by elimination of any one of these three causal components.

Keeping the sward healthy and reducing the conditions that favour disease will be the first priority to keep fairy ring from the turf. The following actions should help achieve this:

  • Carry out programmes of aeration to help keep the surface free draining.

  • Inspect and monitor existing surface water drainage systems; ensure that they are working.

  • Prevent moist conditions remaining on the surface by brushing/sweeping/switching the playing surface (remove dew).

  • Apply a balanced fertiliser to keep the sward healthy. A soil analysis will identify fertiliser requirements.

  • Control thatch layers as thatch provides a good environment for the disease. Reduction of thatch by hollow coring and scarification.

  • Reduce the return of clippings. An accumulation of dead matter will increase thatch.

  • Maintain Soil pH between 5.8-6.5; do not allow the soil to become alkaline.

  • Check mowing heights and keep blades sharp.

  • Be vigilant and treat the disease early to prevent severe attacks. Treat with approved fungicides.

  • Reduce shade.

Chemical Control

Diseases can often be difficult to control. Most IPM strategies work very well and often involve the use of fungicide treatments to help suppress potential outbreaks of disease. As a general rule, fungicide applications should be made during the first signs of attack, since disease can cause substantial damage in a short period of time. In recent years there has been a decline in the use of fungicides. Recent studies have shown that constant use of fungicides often sees the disease becoming resistant to the fungicide, coupled with the fact that they have become very expensive to use.

These Fungicides are usually applied as a liquid using watering cans, knapsack sprayers and vehicle mounted sprayers. Fairy rings are often very difficult to control with fungicides since the soil in the infected area is almost impervious to water. Some success has been achieved by aerating the soil and drenching the infected area with fungicide.

Presently there are no dedicated manufactured chemical products on the market for controlling fairy rings. Fairy Ring Destroyer (active ingredient triforine) was very good at controlling fairy rings, however this product is no longer available. Most chemical manufacturers are recommending the use of wetting agents and bio-stimulants to improve soil conditions. Applying these products helps the grass recover and reduces the affect of fairy ring symptoms.

Fungicides and chemicals to help control fairy rings.

Most wetting agents are best applied when the soil is moist. generally in the spring and autumn periods.

Aquanova: Wetting agent. Manufacturer Scotts.

Aqua-Aid: Wetting agent. Very effective at low rates for injection into irrigation systems and/or as an additive for tank spraying. Liquid, granular or pellets. Manufacturer Tower Chemicals

Breaker Triple: Wetting agent (contains poloxyalkylene glycol surfactants and soil penetrant). Manufacturer Rigby Taylor.

Heritage: (active ingredient Azoxystrobin ) this product attacks the fungi, blocking the ability of the pathogen to respire causing the fungal cells to die. Manufacturer Scotts.

Ensure you follow manufacturer's directions, health & safety and product data sheets, and comply with COSHH regulations, when using these chemicals.

Fungicides are an effective tool where high quality turf is desired. However, they must be applied with care and accuracy and in the context of a good overall turf management program. Before using any fungicide, carefully view the label for conditions of use including rates, methods of application, and precautions. Never use a fungicide in any manner contrary to its label and be sure that the fungicide will not injure the turfgrass species surrounding the disease problem.

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