UK Turf Disease
The majority of turf diseases are caused by fungal pathogens but some fungi are more strongly pathogenic than others. Many of the common cool season turf diseases are caused by fungi that rely on a weakened plant and therefore reducing disease incidence and severity is often aligned to maintaining a strong sward. With on-going changes to European Legislation relating to pesticide use, it is more important than ever that an integrated approach to disease management is employed and central to this is an understanding that the cultural conditions can limit disease development. Making use of the genetic variation that exists between grass types and cultivars can also minimise disease development through a sward. By managing rootzone quality and using weather information services, it can also be possible to pre-empt disease outbreaks and plan an efficient integrated management strategy.
Microdochium Patch (aka Fusarium Patch), caused by the fungus Microdochium nivale, is arguably the most damaging disease of cool season turf. The fungus can live saprophytically on dead and decaying plant tissues and low levels of disease are possible year-round. Typical symptoms develop on susceptible turf during periods of cool, wet weather and because alternating periods of frost and thaw, drizzle or fog are all ideal for the rapid development of this disease, it tends to be more prevalent during the winter months. During prolonged snow cover, the pale pink fungal mycelium within infected tissues accumulates on the sward and is revealed at snow melt as the typical symptoms of Pink Snow Mould. Microdochium nivale is not killed by frost but its growth may be suspended until temperatures start to increase.
All grasses are potentially susceptible to infection but a sward that is growing under conditions of stress is more likely to develop severe disease. Early symptoms of infection, especially on close mown turf, appear as small mid-brown patches approximately 20mm diameter that will increase to form larger, regular patches that may coalesce to produce large blighted areas of turf. The outer edge of the water-soaked patches may develop aerial fungal mycelium and this can be encouraged by placing a sample of turf in a sealed plastic bag overnight to confirm the activity of the disease. The infected leaf tissue will also support millions of fungal spores that give the turf a slimy feel and they will spread the infection across the sward. On low maintenance turf, the sward may appear generally watersoaked with no distinct patch development. Movement of fungal spores and infected plant tissues can easily spread this disease but infection can only occur if the local environmental conditions allow it.
Unbalanced nutrition, especially high nitrogen, can predispose turf to infection and low potassium availability may also affect disease severity. Leaf wetness is essential for fungal infection and thatch can contribute to this requirement as well as providing a good source of saprophytic nutrition for the fungus.
Where required, fungicide applications can be made to manage disease development and areas that are routinely affected by this disease can be monitored for the best time to begin applications. Greater control may well be achieved by employing a preventative fungicide programme as part of the overall disease management strategy where the disease is especially problematic.
Red Thread is caused by the fungus Laetisaria fuciformis and is a common disease on any nutrient-stressed turf. Unbalanced nutrition or low nitrogen (and potassium) availability is likely to encourage disease development, especially in Ryegrasses which have a high nutrient requirement. This disease develops almost invariably in the leaf tissues forming diffuse, coalescing patches of bleached turf that support characteristic red needles (sclerotia) of accumulated fungal mycelium as the infection matures. The mycelium in these red needles will either perpetuate infection by allowing the fungus to grow on to adjacent plants, or will allow the fungus to survive adverse conditions by dropping in to the base of the turf until favourable growth conditions resume.
Red Thread is common during mild, damp weather and leaf wetness is again important for fungal infection.
To minimise disease development, clippings should be removed and scarification or core aeration can help to reduce leaf surface wetness in thatchy turf and reduce the amount of overseasoning sclerotia that may have accumulated during active disease development. An application of nitrogen to affected turf may be all that is required to allow the disease to ‘grow out’ and because the crown tissues are almost never diseased, quick recovery from even the most extensive outbreaks should be achievable.
Fungicides are not generally necessary in an integrated programme for this disease but the available active ingredients will provide control should application be necessary.
The fungus that causes Take-all Patch in turf, Gaeumannomyces graminis var avenae, is a strong pathogen but it has a weak ability to compete with rootzone antagonists. For this reason, Take-all Patch is often seen in new constructions or in turf where sudden changes in rhizosphere pH may rapidly adjust microbial balance. The fungus typically causes disease in bentgrass turf but has become an increasing problem in meadowgrass swards.
It is a disease that infects the root and crown tissues, causing a decay which results in bronze-coloured patches of turf that may become dominated by less susceptible grasses or colonised by broadleaved weeds. The patches tend to have a definite edge where infected turf abuts a healthy sward and the size of the patches can increase annually to approximately 30cm diameter. Initial infection of the roots will occur during the late spring but turf symptoms will only begin to show during the summer and autumn months.
Infected stem base tissues will reveal mats of dark fungal mycelium and as the infection matures, small flask-like spore producing structures will develop through the leaf sheaths.
The fungus may go unchallenged by rootzone antagonists for several years but eventually, a matured rootzone will encourage so-called Take-all decline which will limit the further development of this disease. One of the key elements essential in limiting disease severity is manganese and regular applications of this micronutrient should be considered in susceptible turf.
The disease can be spread by movement of infected plant tissues and dissemination of spores by air and water. The fungus shows increased growth at high pH and avoiding any small but sudden increase in rhizosphere pH can help to lessen disease activity. Application of acidifying fertilisers and increasing surface drainage will help limit conditions favourable for disease. Because this is primarily a root disease, any fungicide application must be taken up by the roots in order to be effective. A late autumn (as plant growth is slowing) and spring application (as growth is resuming) of an appropriate fungicide has been proposed to provide effective management of the fungus during
The fungus Colletotrichum cereale (formerly C. graminicola) causes a Basal Rot and Foliar Blight infection in weak swards. These diseases are strongly correlated with turf stress. Basal Rot infections developing most often in meadowgrass turf during cool, wet weather and Foliar Blight develop on all grasses during warmer conditions. Water is essential for fungal infection and therefore even with the Foliar Blight, a wet leaf is necessary for disease to develop.
Basal Rot infection develops in the crown tissues, reducing water and nutrient movement through the plant and forcing the development of stressrelated yellow to orange/red leaf tissues that typify this disease. Large areas of turf can become diffusely affected by this disease and turf loss is not uncommon. During Foliar Blight infections, the sward becomes colonised by the fungus which causes a diffuse, tan/grey leaf discoloration that appears to darken as the infection matures and as fungal spores are produced on the infected sward. Foliar Blight often develops in turf above a water-repellent rootzone because applied water remains at the base of the turf, allowing development of the humidity required for infection.
Nutrient stressed turf is prone to Anthracnose development and Basal Rot is encouraged by a wet, compacted rootzone. That said, even where Anthracnose is active, water availability must not be restricted because infected plants will die from drought stress. Therefore, the key to managing Anthracnose is to maintain adequate moisture, apply light, regular applications of balanced and complete nutrition, increase the mowing height and avoid any abrasive grooming or topdressing applications. Anthracnose diseases are stress related and therefore you need to minimise all abiotic stresses. There are no resistant grasses or cultivars but a diverse sward will tend to have less severe infection. Fungicides will be effective if they are applied at the correct time. With this disease, preventative applications can often mean less overall fungicide has to be applied to establish control. A combined application of a systemic product with a contact or localised penetrant will provide control but repeat applications may need to be made in turf that is especially susceptible to infection.
Although Dollar Spot has long been recognised as a turfgrass disease, the fungus (or fungi) that cause the disease is (are) still being investigated. Researchers at Rutgers University, New Jersey, have recently renamed the fungus that causes Dollar Spot in turf across the US as Clarireedia homoeocarpa. However, there is on-going debate as to whether the causal fungus for Dollar Spot outside the US is the same organism and therefore we will continue to use the name Sclerotinia homoeocarpa for the fungus that causes Dollar Spot on turf across the EU. Historically Dollar spot was considered to be a disease of slender creeping red fescue, but across Europe it is recorded as causing damage to most turf species (especially bentgrasses) and it now appears likely that different fungi will be named for causing the disease in cool and warm season turf.
Typical Dollar Spot symptoms of straw-coloured turf in coalescing patches (approximately 20mm diameter) tend to develop very rapidly during periods of high daytime and low evening temperatures and the presence of dew on the sward. Individual leaves may demonstrate so-called hourglass lesions where the pale and constricted leaf blade is bordered by a darker band of tissue. However, this symptom is not often seen in affected meadowgrass plants. When the disease is active, fungal mycelium will grow out of infected tissues towards adjacent healthy plants and in doing so, form ‘cobwebs’ of mycelium across the turf. Often the disease is more severe when it develops on nutrient and drought stressed turf but the damage is generally confined to the leaf. This is a reoccurring disease and management of the symptoms should begin by ensuring adequate water and nutrient availability. Preventative fungicide applications are most effective and access to disease forecasting programmes will be important where this disease routinely reoccurs.
There are known to be over 50 Basidiomycete fungi that can cause the development of fairy rings and the severity of the symptoms expressed on the turf will depend on the fungus that is causing the problem. These fungi will colonise either the base of the turf (superficial fairy rings or thatch fungi) or the rootzone and when colonising the rootzone, may result in a range of above-ground symptoms. We tend to refer to the most damaging rings as Type 1 and in these, the accumulation of fungal mycelium can eventually lead to areas of dying turf or bare ground that are bordered on both sides by stimulated turf growth and on their outer edge, may become colonised by fungal fruiting bodies (mushrooms / toadstools). Slightly less damaging to turf quality are the Type 2 rings where stimulated rings or arcs of turf may or may not be associated with fungal fruiting bodies and the least damaging of all are the Type 3 rings that show no change in turf quality but are visible only by the development of the mushrooms / toadstools. In all cases, removal of the immature fruiting bodies by mowing or brushing will help to limit further spread of the fungus.
Some fairy ring fungi can grow to several meters in depth in open, high sand content rootzones and here the symptoms on the over-lying turf can become extreme.
All of these fungi obtain nutrition from dead and decaying plant material and in breaking down the plant remains, the released nutrients are taken up by the fungus for its growth. Some nutrient will also be taken up by the turf roots and this results in some of the stimulated plant growth. The developing fungus grows radially outwards from a central point, increasing in mass as it does so. The old fungal mycelium towards the centre of the rings will eventually die and release nutrient back in to the soil. This release of fungal cell contents is also responsible in part for the stimulated
The fairy ring fungi will cease growth only if they run out of nutrient on which to feed, a solid barrier or disturbed ground. If two rings grow in to one another, they ‘mutually inhibit’ each other’s growth and a figure of eight will develop. If similar growth continues to occur,
arcs and ribbons of fairy rings will develop.
One of the main problems with fairy ring growth is the development of water-repellent soil and this can result in the turf being unable to access water and nutrient. Management of fairy rings is strongly aligned to managing rootzone repellence. The sward in fairy ring affected areas can often develop foliar fungal diseases including Microdochium Patch, Red Thread and Anthracnose Foliar Blight as a result of the stimulated plant growth or water related stress that is associated with different phases of fairy ring development.
Management of fairy ring symptoms includes being aware of the depth of fungal infection through the rootzone. Rootzone core samples taken to depth can be used to determine the depth of water-repellence through the profile and any applied wetting agent (surfactant) will need to be watered in sufficiently to penetrate the affected depth. Often, wetting agents will need to be routinely re-applied to affected areas and the initial application should be made prior to the rootzone becoming dry. Any applied fungicide with labelled efficacy against fairy rings will need to be positioned sufficiently deep in the profile as to reach the fungal mycelium. Due to the observed mutual inhibition of fairy rings, there is a possibility that removal of the turf and rotovation of the affected rootzone could lead to the fungus effectively killing itself out. There is always the possibility that this approach will result in the occurrence of an increased number of small rings so care should be taken before this is considered!
All turfgrasses are susceptible to infection by one or more fungi that cause leaf spot diseases. Most Leaf Spot diseases on cool season turfgrasses are caused by Drechslera species of fungi and foliar infection will result in the development of small, discrete spots or lesions that often have a dark coloured border. The size of the lesions or severity of the overall infection will depend on the relative susceptibility of the host plant and virulence of the specific fungus. Certain diseases, such a Red Leaf Spot, develop only on one grass type (Agrostis) and therefore identification of the affected grass can often help with the identification of the disease. Symptoms can develop at any time of the year but a wet leaf surface is required to enable infection and this often means that symptoms become increasingly apparent during the spring and autumn months or on shaded turf. Quite often, disease develops rapidly in a dry, thatchy turf that is rewetted due to rainfall or irrigation. The fungi that cause these diseases are capable of living saprophytically in dead plant tissues and previously infected material acts as a good source of inoculum. In certain Leaf Spot infections, the fungus can develop in to the crown tissue and this will result in a decay or ‘melting out’ of the affected areas of turf.
Most leaf spot infections will not cause severe damage to the turf and can be effectively managed by application of balanced nutrients to encourage the turf to grow away from the disease and removal of infected clippings when mowing. However, if Leaf Spot is a problem in stadia, for example, where shade and humidity may not be easily managed, application of fungicides may be needed to prevent continued disease development and loss of visual turf quality.
Since the fungi that cause Leaf Spot disease may be relatively host plant specific, the use of different grass types or cultivars can help to reduce disease severity in a given area.
Rhizoctonia Blight (Brown Patch)
This disease, caused by the fungus Rhizoctonia solani, is not too common across the UK because high temperatures (20 to 30C) and high humidity (leaf surface wetness) are required for infection and disease development. That said, it may occur during the summer months and has often been seen in stadia environments. All grasses may be affected but the development of symptoms will vary with grass type and height of cut. On close-mown fine turf, tan coloured circular patches may develop a dark, water-soaked appearance and can be anywhere between 5cm and 60cm diameter. On longer swards, the watersoaked plants may collapse and form large areas of blighted turf, usually without a darker border. Patches can increase in size and coalesce if conditions remain favourable and will be spread by movement of infected leaf tissue (mycelium) and mycelial mass (sclerotia). The disease most often develops on turf that has received high levels of nitrogen application but infection seldom develops in to the crown tissues.
The disease incidence can be minimised by maintaining adequate & balanced nutrition and by reducing the period of leaf surface wetness. Fungicides are generally not required to manage this disease.
Brown Ring Patch (Waitea Patch)
The fungus Waitea circinata var circinata causes the development of tan/yellow – brown rings on cool season turf from late spring to late summer when temperatures reach approx. 16C. It is often referred to as a Rhizoctonia-like fungus due to its formal classification and the ’typical’ Rhizoctonia mycelium appearance under the microscope. The symptoms tend to develop more severely under conditions of low nutrition and on turf maintained under moisture stress. In the UK, symptoms have so far only been seen on Poa turf, but Agrostis has also been recorded as being susceptible to this disease.
The symptoms appear very similar to those of superficial fairy rings but the typical fairy ring smell is not present in turf affected by this disease. The fungal mycelium tends to develop rapidly around the leading edge of the symptoms following overnight incubation of a turf sample under humid conditions.
Disease development can be minimized by maintaining adequate rootzone moisture and nitrogen input and where the disease is expected (or following initial symptom development) weekly applications of low amounts of nitrogen can significantly reduce severity of the disease. Fungicide applications may be required as part of the management programme and DMI fungicides have been shown (through US research) to provide good long term control although if applied alone, they may take a while to kick in. Applying combined products should provide good initial control of the symptoms and lasting control of disease development.
Yellow Tuft (Downy Mildew)
This disease is caused by the fungus Sclerophthora macrospora and is most commonly seen affecting bentgrasses although it often develops in Poa annua plants and can affect all cool-season grasses. The most advanced symptoms of this disease are generally expressed in the spring or autumn months as excessive tillering through infected plants, giving the sward a mottled, tufted appearance. Typically, affected plants are chlorotic and have noticeably diminished root development allowing them to be pulled easily from the sward. Symptoms develop rapidly if there is free water around the base of the turf. Poor surface drainage will exacerbate the symptoms. Because S. macrospora is an obligate parasite, the fungus will always remain inside infected plant tissues but will only cause significant symptom expression when environmental conditions are favourable. In the early stages of development, the presence of the fungus may be expressed as small, red-brown marks on the leaf blade with no apparent effect on tillering and this symptom can be mistaken for Leaf Spot disease. Yellow Tuft is most often seen on close mown fine turf and because fungal activity increases with water availability, areas that tend to sit wet or that are in the path of water movement across a surface, will be first to express the symptoms.
Control of this disease should focus on water management around the base of the turf and through the upper rootzone profile. The severity of the symptoms will increase as water availability increases and therefore, by focusing on improved water management, the symptoms will be reduced. Fungicide application is not necessary.
Rust diseases are generally caused by fungi in the genus Puccinia but some Uromyces species of fungi can also cause rust disease in cool-season turf. These fungi are so-called obligate parasites and only develop in living plant cells. For this reason, although the symptoms may appear severe (due to the quantity of spores that the fungus can produce), turf is not likely to be killed as a result of a disease outbreak. Rust fungi are extremely well specialized parasites and may have a life cycle that includes up to 5 different spore types. However, when disease is active in turf, there tends to be a cycling of one spore type which allows rapid development and spread of the fungus. Disease may develop in all turfgrasses but it is perhaps more common (and important) in Poa pratensis and in Lolium perenne. Initial symptoms appear as a slight leaf chlorosis but rapidly, small blisters (pustules) will be seen along the leaf blade and these eventually rupture to release their orange fungal spores. Symptoms begin to develop through the warm, dry summer months and typically show on nutrient and / or moisture stressed turf. The disease can generally be managed effectively by removing clippings and adjusting nutrient and water input. That said, the fungi can develop a specific relationship with their host and individual ‘strains’ or races of the fungus may develop on a specific grass cultivar. For this reason, including more than one cultivars in area that is prone to Rust infection can help to minimize the development of disease symptoms. Fungicides are rarely necessary to control Rust diseases.
This is a relatively new turf disease to affect cool-season grasses and it is caused by an organism that is not a fungus. Labyrinthula terrestris is the only known species of the genus Labyrinthula that causes disease in terrestrial plants. Other pathogenic species cause disease in marine environments and therefore unsurprisingly, Rapid Blight development in turf is strongly correlated to rootzone salinity. Individual cells of L. terrestris are spindle-shaped and colonise plant root and leaf tissues. They cause an initial watersoaking of the plant which may lead to areas of infected turf with general symptoms similar to those of Anthracnose or Microdochium Patch and Poa is the most susceptible grass type. Other grasses including ryegrasses and most bentgrasses may also become badly affected but salt-tolerant bentgrass cultivars and fescues appear to be less susceptible. Depending on the sward composition, height of cut and salinity level, the disease may spread rapidly to kill an entire putting surface in a few days. Symptoms can develop at any time but as rootzones dry out during the summer months, symptoms development can be rapid. Early diagnosis of the symptoms is crucial for the management of this disease because only pyraclostrobin, mancozeb* and trifloxystrobin have so far shown good control (in US trials) and efficacy increases if applied early in disease development. Management of soil and water salinity is important and rainfall remains the best method of control.
*mancozeb is not currently approved for use on Managed Amenity turf in the UK
Plant Parasitic Nematodes
Over the last decade, we have become increasingly aware of the potential problems to turf caused by high populations of plant parasitic nematodes (PPN). PPN are obligate parasites, feeding only on living plant tissues. They have long been recognised as causing damage to warm-season grasses but research has now identified many different species that are frequently present in cool season turf. PPN populations will naturally rise and fall during the year and population growth is strongly affected by temperature. They are able to migrate vertically or horizontally to avoid unfavourable conditions or to locate more productive feeding sites. PPN are aerobic organisms that require a film of water through which to move and their populations can rapidly build in high sand content rootzones.
PPN can be divided in to either endo-parasites that spend most of their life within plant tissues or ecto-parasites which remain in the rootzone whilst feeding on plant cell nutrients. They may also be migratory or sedentary in their feeding habit and most PPN that affect turfgrasses, do so by feeding on or within the roots. There are a small number of PPN that colonise the stem base or leaf tissues but little is currently known about relative population damage.
PPN feed by inserting a hollow spear (stylet) in to the plant tissues, introducing compounds to maintain their feeding sites and removing the plant cell content. They can significantly and adversely affect the plants biochemical balance to sustain their parasitic behaviour.
The most damaging PPN are the so-called sedentary endo-parasites known as the Root-knot (Meloidogyne spp.), Cyst (Heterodera and Punctodera spp.) and Root Gall
(Subanguina sp.) nematodes. The Root Gall nematode is largely restricted to infection of Poa species but all grasses are susceptible to infection by the other two. Induced changes in root structure and function directly affect plant growth and development, resulting in a weak sward that is likely to show symptoms of stress. The lesion nematode (Pratylenchus spp.) is a migratory endoparasite that causes significant damage to root cortical tissues. There are a large number of migratory (and occasional sedentary) ecto-parasites that can feed on turfgrass roots and some can benefit from endo- and ecto-parasitic behaviour. Because most PPN affect water and nutrient uptake, visible turf symptoms often resemble drought or nutrient stress. By maintaining a strong and healthy sward, the turf is more capable of tolerating the feeding activity of high PPN populations. Resent research has shown that reducing turf stress through biostimulant application, can reduced the damage done by these parasites.
There is presently one product available with approval to control PPNs but several soil amendments have been seen to suppress PPN populations.
There are several different types of moss that can cause problems in amenity turf, but they generally colonise a weak sward. These are usually scalped, worn, nutrient deficient, drought stressed or wet turfgrass areas.
Mosses belong to a group of plants called Bryophytes which like most plants contain chlorophyll and photosynthesise to facilitate their growth and development. However they do not have typical roots but possess so-called rhizoids that help to anchor them to the ground and take up water directly through their leafy surface. Moss plants don’t produce seed but release microscopic spores that can easily be spread across the turf and enter the profile to depth. The vegetative parts of the moss plants can also serve to increase its composition in an infected sward.
Moss can be a problem in turf all year round but its presence in the sward will be more apparent if turf becomes weak. The silver thread moss Bryum argenteum is a common problem on weak or worn turf areas and once in the sward, it can rapidly become established and very difficult to remove. This moss in particular can have a significant and detrimental effect on the visual and playing quality of a close-mown, fine turfgrass surface. Other moss species have a more open growth habit than that of B. argenteum, but all moss invasions will change the quality of the playing surface and should be targeted for removal as soon as they are seen.
Effective and long-term control of moss in turf relies heavily on producing a strong sward that will out-compete the moss plants. It is often said that ‘moss invades a problem and then becomes a problem’. Products aimed at weakening the moss plants should be applied when the rootzone is moist and when the moss is actively growing. One to two weeks after application, the moss plants should become darker in colour or show reduced vigour. These weakened plants can be removed by scarification and the sward encouraged to fill in through the thinned areas, thus reducing the conditions favourable for re-establishment of the moss. Since moss rhizoids can typically colonise the upper 20-30mm of the rootzone, deeper scarification will be necessary to remove the moss fragments and reduce its impact on the sward. The upright and compact nature of B. argenteum in particular makes this a challenging moss to remove because applied products are not likely to wet / penetrate the plants but be dispersed across their surface.