Watch out! There may be some disease about

Laurence Gale MScin Pests & Diseases

After such a pleasant summer, we are now entering the autumn phase of our seasonal year.

Recently, we have seen evening air temperatures dropping dramatically, especially when we have clear cloudless nights, resulting in heavy morning dews on our playing surfaces.

Dew forms when a surface cools to a temperature which is colder than the air next to the surface. Dew is water that has condensed from some of the water vapour contained in the air. If the layer of air next to the ground were actually cooling, then fog would form. Instead, it is just the surface (for instance, grass) that is cooling, and a very thin layer of air next to the grass deposits some of its water vapour on the grass.

The combination of early morning dews, warm and wet weather and diminishing daylight hours increases the risk of fungal disease outbreaks. The right conditions to trigger these disease attacks are weakened or susceptible plants, a disease-producing organism (pathogen usually fungi) and weather conditions which favour the formation of fruiting bodies and spores (moist, mild wet conditions).

Most cool season turfgrass diseases spread via water droplets. Plants also release excess nutrients via their stomatas (gutation) during night hours when there is no sun and rarely any wind to evaporate it. These exudates become mixed with the dew water and become the perfect food source for disease pathogens in their early stages of development.

The majority of diseases that are occurring now have responded to the unusually warm, autumn weather conditions. Boundary layers around the leaves have stayed very moist and humid. Relative humidity is important for spore germination and penetration of leaf tissues, and constant wet conditions will allow the development and transportation of active fungi spores.

Most fungi grow well between 10°C - 40°C and function best at a pH range of 4-7pH. The current lack of cooler weather and sharp frosts has not helped in reducing these active pathogens.

The first step in turfgrass disease management is identifying the true nature of the problem. Diseases are only one cause of turf loss, and disease control measures will do nothing to alleviate damage from other causes such as management, wear or plant stress. It is therefore essential to determine whether the problem is disease, and if so, which disease.

The three disease factors: susceptible grass / host, pathogen, and environment, provide the evidence for disease diagnosis. Symptoms are the expression of the susceptible grass to the disease and can take on a variety of forms.

Symptoms may appear on the leaves as small, circular, tan-coloured lesions surrounded by brown or purple borders (leaf spotting); as yellow, red, or tan blotches over most or all of the leaf blade (blighting); stunting; wilting; or as a brown or black rot on the crowns and roots. The appearance of these symptoms will also vary depending on the type of disease, the severity of the attack and the developing stage of the disease.

Early identification of the symptoms is essential for good disease management, however the best form of management is using preventive, cultural turf maintenance methods that reduce the ideal environmental factors that these diseases require for development, e.g. regular brushing/switching of the grass to remove excess moisture, regular aeration to allow gaseous exchange and water percolation.

Over the years, we've developed many methods of removing dew from playing surfaces, from dragging hose pipes over pitches to switch canes on bowling and golf greens. However, these laborious tasks have been superseded with the development of brushing attachments that can be fitted to both mowers and gators to speed up operations, though hand switching also gives you an opportunity to get close and personal and keep an eye on what's happening.

Other cultural methods to help reduce disease pressure would be removal of thatch, which harbours pathogens, by verti-cutting and end of season renovations, as well as checking mower blades are sharp to provide a precise cut of the leaf blade and reduce the potential for disease.

Identification of these diseases can sometimes be difficult in the early stages of attack. It's often only possible to recognise the type of disease when the fruiting bodies of the disease produce structures such as spores, mushrooms, or mycelium (small, thread-like filaments produced by fungi) that can be seen without the aid of a microscope. A good example of this is Red Thread (Laetisaria fuciformis) where the distinctive red filaments can be seen amongst the grass.

Site characteristics and turf management practices have a large influence on disease management. Factors such as air movement, drainage, soil conditions, and the amount of sun or shade, slope, fertilisation and aeration programmes are important in influencing the development of turf diseases.

It is important to remember that pathogenic fungi can survive and remain in a dormant state in plant debris and soil until favourable conditions arrive again to stimulate another disease outbreak.

The pathogens that cause these diseases are always lying dormant, waiting for the ideal conditions to become active. Once these spores are activated, and have found an appropriate host, they are able to grow and reproduce themselves, spreading new spores and infections to other areas of turf. This cycle continues whilst favourable conditions prevail.

Understanding and implementing works that can break up the disease cycle will help reduce the opportunities for disease development and outbreak.

When it comes to disease identification, there is as much emphasis on you, as the turf manager, to provide appropriate turf samples for analysis as there is for the lab to accurately identify the problem. In most cases, the best place to remove a turf sample for analysis is from the leading edge of the symptoms, where the affected or discoloured plants give way to healthy turf.

It is also important for the lab to be able to see what the general composition and condition of the sward is like and what the rootzone profile is like and, for those reasons, a 90mm diameter core sample, taken to a depth of approximately 60mm using a golf hole changer (or similar) makes for an ideal sample.

If possible, email photographs of the symptoms so that the lab can get an idea of how the problem is developing - a good picture can often tell so much more than a detailed written description.

There are a number of excellent laboratories that offer disease recognition, along with some good weather services that offer disease watch forecasts. One we recommend is Syngenta's Greencast service.

Common diseases that can be active and cause concerns at this time of the year are: Red Thread, Fusarium and Dollar Spot.

It is important to have identified the disease correctly, so that an appropriate fungicide can be selected. Using the wrong fungicide or wrong application rates can lead to a number of problems, not only would it be a waste of time and money, the effect on the disease is likely to be negative and may well exacerbate the problem by making the disease more resilient to the active ingredient applied.

Red thread spores (2)
Red thread Laetisaria fuciformis (Pathagen)

Red thread is often seen during the summer/autumn months, but may persist into the winter months if conditions remain mild, temperature range 15-24°C.

Identification of the disease is relatively easy with the turf grass having, irregular tan coloured shaped patches of damaged or necrotic grass varying in size 20-350mm with a pink/red colour cast caused by the fine red filaments/needles (10mm long) of the mycelium of the pathogen. Severe attacks will damage/kill grass.

Red fescues: slender and strong creeping red fescues (Festuca spp.), Perennial Ryegrass (Lolium perenne L.) are the main susceptible species affected by red thread. Other grasses which can be affected are bentgrasses (Agrostis spp.) and annual meadowgrass (Poa sp.) The above grasses are used in most sport turf situations including golf, bowls, cricket, and winter games pitches.

Fungus spores can remain viable for up to 2 years, survive temperature as low as -20°C or as high as 32°C, This fungus is capable of growth at pH 3.5 -7.5; this means that the disease can occur on almost any amenity turf rootzone.

Red Thread spores (sclerotia) and (arthroconidia) are spread by wind, water and by traffic, and it is during these periods of mild, cool, wet weather, with temperatures 0-25°C and heavy dews, that an outbreak of disease takes place. Attacks appear during summer/autumn months but can persist into winter if weather remains mild. These spores germinate into mycelia, infecting new plant tissue, then reproduce to form fruiting bodies red threads (sclerotia).

Turf grass is susceptible to disease attack when damaged or under stress from low fertility, slow growth (insufficient Nitrogen), drought and compaction. Keeping the sward healthy and using resistant turf grass species will reduce the incidence and severity of disease attacks. Apply a balanced fertiliser programme with emphasis on nitrogen input, ensuring not to over fertilise in autumn as this may lead to other pathogens attacking the sward.

Maintain an open sward, by aeration and scarification which will, in turn, reduce thatch. Maintaining mowing machinery and removing morning dew by brushing are all good cultural practices in keeping Red Thread at bay. As a last resort, an application of an approved fungicide can be used. Approved manufacturer products available for application are contact and systemic pesticides, with the following active ingredients Iprodione, Thiophanate-methyl, Thiabendazole and Carbendazim.

With the correct Integrated Pest Management programme (IPM) in place, Red thread will not be a major disease problem on turf. Grass generally recovers well from this disease after treatment.

wrekin golf club 1 feb 2005 007
Fusarium (Pink Snow Mold) Microdochium nivale (Pathagen)

Fusarium patch disease is becoming very widespread on amenity sports turf facilities, particularly during the winter months. Its symptoms are more easily seen on fine turf situations of bowling and golf greens. The disease appears as small orange/brown colour, circular dead patches/spots up to 25-50mm in diameter.

Fusarium patch is often seen during the late autumn/winter months when cool and wet weather and moist surfaces persist. The pathogen can be active across a broad range of cooler temperatures. Identification of the disease is relatively easy, with the turf grass having irregular tan/orange coloured shaped spots of damaged or necrotic grass varying in size 20-350mm, with a pale pink/white colour mycelium. Seen when the disease is active, the initial symptoms are small brown spots, which will rapidly enlarge and cause scarring of the turf when conditions are favourable. These scars will be difficult to heal and repair during the winter months, so early recognition and treatment is important to reduce scarring of the turf surface.

All mature amenity and sports turf containing the following grass species will be susceptible to an attack of fusarium: Agrostis spp. (Bent grasses), Festuca spp (Fescue grasses), Loluim spp (Rye grasses), Poa spp (Annual meadow grasses).

With Poa species being the most commonly attacked, however, this grass is able to recover easily after an attack because of its seed bank presence in the soil. The above grasses are used in most sport turf situations including golf, bowls, cricket and winter game pitches.

Fusarium patch spores (sclerotia) and (arthroconidia) are spread by wind, water and by traffic, and it is during periods of mild, wet weather and heavy dews that an outbreak of disease takes place, with attacks appearing during late autumn and through the winter. These spores germinate into mycelia, infecting new plant tissue (pale pink and white mycelium), which can be seen around the edge of the patches, indicating that the disease is active.

Turf grass is susceptible to disease attack when damaged or under stress, and when the soil surface remains wet during prolonged periods of wet cool weather. In severe infections, the fungus may penetrate as far as the crown, but will usually not kill the plant. If the plant does die, it is more likely from subsequent winter injury or another cause. Infected turf will recover when the plant becomes more active in the spring and is able to produce new healthy leaves, restoring its vigour and colour.

Keeping the sward healthy and reducing the conditions that favour this disease will be the first priority to keep it from your turf. There are a number of UK approved fungicides that can be used for treating fusarium; all should be applied in accordance with manufactures recommendations, product data sheets and COSHH regulations (Control Of Substances Hazardous to Health).

Dollar Spot
Dollar Spot Sclerotinia homoeocarpa (Pathagen)

Dollar spot is a fungal disease that appears to be increasing in occurrence across the UK. Historically, Dollar spot has been recorded as a disease of fine-leaved fescues but, in recent years, we have seen a steady rise in the number of outbreaks of this disease developing on Poa annua swards.

This fungus causes rapid outbreaks of disease on turfgrasses under a range of mowing heights but, on close mown turf, the symptoms can be dramatic. The characteristic small (2cm diameter) bleached spots of infected turf can develop so extensively that it can be difficult to stand on an area without putting your foot on the diseased plants.

Dollar spot can develop either during late spring/early summer or late autumn, but more severe outbreaks appear to develop in the autumn. Drought-stressed turf is particularly susceptible to infection, but water, high relative humidity or heavy dew are necessary for disease development.

The disease shows as 2 to 4cm diameter bleached spots which do not increase much in size but which do coalesce to form large areas of bleached turf. In all grasses, apart from Poa, individually affected leaves show a characteristic 'hourglass' lesion which can be seen as a bleached, slightly narrowed portion of the leaf, bordered at each end with a narrow, dark band. In Poa, the bleached lesion is present but the dark borders are not.

Management of this disease is based around cultural controls. Thorough deep, but infrequent irrigation is recommended as a way of providing sufficient water to the plant whilst reducing the overall period of leaf wetness. Removal of dew is essential to minimise the chance of infection. Adequate nitrogen nutrition is critical, both to minimise the onset of the disease and also to aid recovery of an affected sward.

Several fungicides that are currently available for use on managed amenity turf have shown efficacy against this turf disease and, where necessary, can be used as part of an integrated programme to manage dollar spot. Always ensure that the disease is correctly identified prior to the application of any plant protection product.

However, we must recognise that by achieving good cultural practices to reduce thatch, improve air movement in soils, balanced feeding and correct mowing regimes, will play an important part in promoting a vigorous healthy turf that can fight off and reduce the chance of disease attack.

We have also seen, in recent years, a trend towards more use of alternative products such as organic fertilisers, compost teas, use of phosphite as well as tonics and bio stimulants to improve turf grass quality and help reduce disease incidence.

Good cultural practices may be the only option for disease control in the future, especially as there are moves to reduce the amount of chemicals and fungicides available for use in the coming years. However, at the moment, we are still able to reduce fungi pathogen populations by applying fungicides which either kill off the pathogen or slow down the production of fungal spores.

Again, it is important to have identified the disease correctly, so that an appropriate fungicide can be selected. Using the wrong fungicide or wrong application rates can lead to a number of problems. Not only would it be a waste of time and money, the effect on the disease is likely to be negative and may well exacerbate the problem by making the disease more resilient to the active Ingredient applied.

Fungicides can be divided into two broad categories: contact fungicides and systemic fungicides. The contact fungicides generally are applied to the leaf and stem surfaces of grass plants. These materials may or can be washed or mowed off easily, which implies that they often only have a short term active durations, between 7-10 days. These fungicides are usually used to control foliar diseases and not diseases of the root and crown structures of the plant. Contact fungicides are used throughout the twelve months of the year. A complete range of fungicides are available from the Pitchcare Shop.

Systemic fungicides have a different mode of action; the chemicals are absorbed and translocated within the plant's tissues. Thus, they are not as likely to be removed from the plant by rainfall and mowing. Therefore, they are active for longer periods and can protect plants for up to 4 weeks. Most systemic fungicides can control both foliar and root/crown diseases. Use of systemic fungicides during colder months is not advised, as the plant is either dormant of slow growing and will not rapidly uptake the fungicide, greatly reducing its effectiveness.

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Pests & diseases