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In this short article, I want to focus on three diseases of turf that we may see in the summer months, if the conditions are right, writes Graham Paul.
Starting with Red Thread – probably the most common of the three in the UK and certainly an easy one to identify. Red Thread produces ill-defined patches of bleached grass along with a pink mycelium that is sometimes visible in early morning dew. Close examination with the naked eye will often reveal red needle-like structures attached to the leaf blades, which give rise to the name ‘Red Thread’.
I first encountered Red Thread on turf during the late 1970’s whilst involved in trials with a fungicide product called Rovral Green. Then the disease was referred to as ‘Corticium Disease’, a reference to the fungal species that caused it – Corticium fuciforme. The genus Corticium was established by Persoon in 1794 for fungi that have “smooth, effused fruit bodies”. In recent years the academics have tinkered with the classification; the same culprit is now known as Laetisaria fuciformis. Mycologists believe the disease occurs in two distinct stages; the first produces pink mycelium in clumps that are usually found where two blades of infected grass meet. The second stage gives rise to thin red needles, a form of sclerotia known as ‘stromata*’ that enables the fungus to survive adverse conditions, such as drought and low temperatures (*Not to be confused with the leaf organs called stomata). When favourable conditions return, the stromata germinate producing invasive mycelium that enters the new host plant through the stomata on the leaf surface. Stromata can remain viable in the soil for two years.
In 1982 a paper was published in the Canadian Journal of Botany by J.A Stalpers & W.M Loerakker announcing that the disease ‘Pink Patch’ had been isolated from samples of Red Thread affected grass. Pink Patch is caused by Limonomyces roseipellis and was previously thought to be part of the Red Thread disease. Current thinking is that Pink Patch can occur on its own or in a complex with Red Thread. Pink Patch spreads much more slowly than Red Thread, is less severe, and does not produce cottony flocks of mycelium or the stromata that are a means of survival; instead, individual leaves become covered with a pink, gelatinous mycelium that can survive for long periods on plant debris.
Both Red Thread and Pink Patch are caused by fungi belonging to the Basidiomycota, a taxonomic division within the kingdom Fungi comprising some 30,000 species that produce spores from a basidium (a club-like structure found in Basidiomycete fungi, where the spores are produced and held prior to dispersal.) This large phylum contains the cap (mushroom) producing fungi – most notably the fairy rings that we see on turf, as well as Grey Snow Mould, Thatch Fungus (Superficial Fairy Ring), rusts and smuts.
1/4 - Red Thread often occurs in areas of low soil fertility.
2/4 - Rusts infect grass, producing large quantities of spores.
3/4 - From a distance Rust can appear as a patch of stressed turf.
4/4 - A close up image of a Rust infected grass plant.
Red Thread and Pink Patch both occur in similar conditions of slow grass growth that is usually the result of low soil fertility, especially soils that lack nitrogen. They are favoured by warm moist conditions especially in summer and early autumn but the disease can persist into mild winters. We often see outbreaks of Red Thread on turf after prolonged showery weather. On sandy soils this may be the result of persistent rain diluting or just moving the nitrogen away from the roots. On heavier soils it may be the result of waterlogging causing a depression in grass growth vigour.
Many Greenkeepers and Groundsman will be reassured by the odd patch of Red Thread in the early autumn, as it indicates that the soils are not too rich in nitrogen, which can trigger an attack of Microdochium Patch (fusarium patch). Most grass species are susceptible to Red Thread and Pink Patch, especially Red Fescue and Perennial Ryegrass. Although disfiguring to the appearance of turf, these diseases rarely kill the grass, which can usually be returned to good health following the application of appropriate control measures.
Sometimes, all that is required is a thorough programme of aeration to release nutrients locked up in the soil by anaerobic conditions. The application of a good quality seaweed extract or other bio-stimulant to promote strong root development can also help to discourage these diseases. Improving the nutritional state of the soil by careful application of a nitrogenous fertiliser is often prescribed as a remedy for Red Thread but beware of putting on too much nitrogen during the critical period at the end of summer, when it is all too easy to tip the balance in favour of soft growth that may bring on an outbreak of Michrodochium Patch.
Where Red Thread occurs on a regular basis, consider using cultivars of grasses that have been bred for greater resistance to the disease. The British Society of Plant Breeders (BSPB) produce a booklet each year titled “Turfgrass Seed”, based on the grass seed trials conducted at the STRI in Bingley, West Yorkshire. The tables in this booklet give scores on resistance to Red Thread for many of the grass species tested, including all of the most susceptible ones such as Red Fescue and Perennial Ryegrass. The booklet can be obtained from most amenity distributors selling grass seed or as a pdf download from the internet (Search: ‘Turfgrass Seed 2014’).
Chemical control can be achieved by applying an appropriate fungicide but I always ask customers to think long and hard before using one for Red Thread, when cultural measures such as those described above will usually bring the problem under control. Every application of fungicide has some effect on the balance of microorganisms in the soil, despite what some manufacturers may claim about “products being harmless to beneficial microbes”. For some disease problems there is no alternative to the prudent use of a fungicide spray but where the pathogen doesn’t usually kill the grass and other measures are available, then we should show restraint.
The second part of this article involves a condition we refer to as rust, which can be caused by a number of different fungi. Rusts infect grass producing large quantities of spores, varying in colour from yellow through orange to dark brown, depending on the fungal species involved. Rust is not a common problem on UK turf because it develops in response to unusual weather patterns.
However, when it does occur rust can spoil the appearance of the sward and large numbers of spores are picked up on footwear, clothing and on sports equipment and maintenance machinery.
Like Red Thread and Pink Patch, Rusts are also members of the phylum Basidiomycota. Subtle differences between the many species of rust fungi make it difficult to generalise the life cycle. However, conditions that favour development of rust are the same; grass whose growth is slow due to poor nutrition and drought stress are prone to rust.
After the initial infection, the symptoms appear as yellow spots or flecks on the stem and leaf. As the disease develops, these spots increase in size, eventually producing raised blisters (sometimes referred to as ‘pustules’), which rupture as they mature and release spores. Depending on the fungal species involved, the pustules may be scattered at random on the leaf or stem or they can be arranged in lines. As the disease gets further into the autumn, the orange or brown rust spores are replaced by less conspicuous black resting spores called teleutospores.
The worst outbreaks of rust disease occur on stressed, poorly nourished turf. Rusts are most noticeable in long grass such as golf rough and semi-rough areas. They are usually seen after long spells of warm weather during the summer and autumn. Other factors that are likely to encourage an attack of rust include; soil compaction, excessive shading by overhanging trees and hedgerows and periods of prolonged drought.
A programme of cultural measures to reduce the possibility of rust disease developing will need to address these influencing factors; ensuring adequate nutrition throughout the summer period and providing supplementary irrigation, where possible, to prevent drought stress. Where it is practical, clipping removal can reduce the level of spores available to prolong the infection and so speed up recovery. In areas where rust is a recurring problem, consider overseeding with cultivars that are less susceptible to rust – some of these are also listed in the BSPB booklet “Turfgrass Seed”.
A few fungicides available for managed amenity grass now have recommendations for the control of rust diseases and these should be included as part of an integrated management programme where the cost can be justified.
References: Stalpers, J.A.; Loerakker, W.M. 1982. Laetisaria and Limonomyces species (Corticiaceae) causing pink diseases in turf grasses. Canadian Journal of Botany. 60(5):529-537
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