\u201cDollar spot attacks all grasses \u2013 it is a significant disease of fine turf in the USA and they are not blessed with fescue-dominated golf courses.\u201d<\/em> (Steve Isaac, The Sports Turf Research Institute, 2007)<\/p>\n\n\n\n \u201cDollar spot is a new disease in Scandinavia. It is caused by the fungus Sclerotinia homoeocarpa. In Scandinavia, we have found two genetic variants of this fungus. One seems similar to that found in the United States, while the other is clearly different. This makes it hard to say how serious injuries we can expect, but it seems clear that the disease may occur at lower temperatures than in the United States\u201d <\/em>(Scandinavian Turf and Environment Foundation, 2015)<\/p>\n\n\n\n \u201c\u2026.this is one of the oldest turf disease problems we know but there is still much that we need to learn about the fungi that cause it\u201d<\/em> (Dr. Kate Entwistle, The Turf Disease Centre, 2018).<\/p>\n\n\n\n \u201cDollar Spot is the most serious disease on golf greens in many parts of the world. Sunken patches, which are often very slow to regenerate, can have a massive impact on the quality of the game\u201d <\/em>(R&A GC2030 Dollar Spot fact sheet in association with Swiss Golf, 2019)<\/p>\n\n\n\n \u201cThe recently developed \u201cSmith-Kerns\u201d Dollar Spot predictive model uses five-day rolling averages of hourly relative humidity and air temperature to generate a risk index (%) for disease development. Applying fungicides at a 20% risk index action threshold controlled Dollar Spot similar to a calendar-based program and reduced applications by one to three sprays per year <\/em>(USGA Green Section Record, 2023)<\/p>\n\n\n\n The classification of the fungus that causes Dollar Spot has historically been recognized as Sclerotinia homoeocarpa. <\/em>The taxonomic classification of this fungus has been under revision and has only recently been re-classified under the name Clarireedia, <\/em>a new fungal genus comprising four pathogenic species responsible for dollar spot disease of turfgrass. Clarireedia homoeocarpa<\/em> is described to accommodate the Dollar Spot fungus. Three new species in this clade, Clarireedia bennettii<\/em> sp., Clarireedia jacksonii<\/em> sp. and Clarireedia monteithiana<\/em> sp. that also cause dollar spot disease are described. Clarireedia homoeocarpa<\/em> and Clarireedia bennettii<\/em> occur primarily on Festuca rubra<\/em> (C3 grass) hosts and appear to be restricted to the United Kingdom. Clarireedia jacksonii<\/em> and Clarireedia monteithiana<\/em> occur on a variety of C3 and C4 grass hosts, respectively, and appear to be globally distributed. This resolved taxonomy puts to rest a major controversy amongst plant pathologists and provides a foundation for better understanding the nature and biology of these destructive pathogens. Dollar Spotattacks the leaves of grass plants andis known to be active between 10 and 35o<\/sup> C. Pathogenicity is most severe between 15 and 25o<\/sup> C and it is when these temperatures are experienced that most damage occurs. Classic symptoms are small bleached, straw-coloured spots are normally no bigger than 50mm in diameter, the size of an old silver dollar coin (Figure 1).<\/p>\n\n\n\n Once Dollar Spot is established extensively in an area, these individual spots can coalesce and form larger, irregular patches. Unlike other common turf grass diseases it is unusual for the individual spots to increase in size dramatically themselves (Figure 2).<\/p>\n\n\n\n Where certain climactic conditions are experienced, dense aerial mycelium can be seen on the affected turf blades early in the morning (Figure 3). Such conditions would be hot days and warm nights, together with high humidity.<\/p>\n\n\n\n As Dollar Spot has not been commonly seen in the UK until recently and as its general appearance can be mistaken for other diseases, it can easily be misdiagnosed but the examination of individual grass leaves can enable a more certain diagnosis. It is upon close inspection that the most recognisable visible symptoms can be seen which set it apart from other diseases. Initial symptoms of attack are small yellow-green chlorotic spots. These spots evolve to form lesions. An infected grass leaf can be seen to be exhibiting one or more lesions, which have a bleached white centre and reddish brown borders (Figure 4). Although they can occur randomly across the leaf, these lesions are classically hourglass in shape and girdle the complete leaf blade. Older lesions may become quite long and cause blighting of the entire leaf or cut leaf end.<\/p>\n\n\n\n A good understanding of the biology of Dollar Spot and therefore its life cycle is key to controlling the disease (Figure 5). The fungus is thought to survive unfavourable conditions as either dormant mycelium in infected plants or as linear black mycelial inclusions in the thatch, these are known as stromata. At this stage, fungal dissemination is therefore restricted to movements of infected leaf debris by equipment, animals, people, wind or water.<\/p>\n\n\n\n When daytime temperatures reach the required level the dormant mycelium resume growth from the infected leaves and can then come into contact with nearby healthy leaves, causing new infections. In such conditions the grass plant exudes sugars and other nutrients during the nighttime in guttation droplets. This provides a nutrient source that the fungi utilise to initiate growth and therefore spread the infection.<\/p>\n\n\n\n If conditions change following initial infection, nights become colder and drier, or control measures are implemented quickly and successfully, infection may not become more severe than scattered leaf lesions. If grass growth is vigorous, the symptoms may disappear after a number of mowings. If however favourable conditions for the disease persist following initial infection, such as warm nights with heavy dews, and if control measures prove to be unsuccessful, severe leaf blade damage may occur and the characteristic \u201cdollar spots\u201d may appear on the turf. When considering the biological aspect of this disease, it is worth noting that leaf and crown of individual plants are affected, whereas the roots and rhizomes are not, therefore in the majority of cases, grass plants are not completely killed by an attack and can recover if correct maintenance and renovation practices are employed.<\/p>\n\n\n\n Experience and research have proved that turf grass disease development is dependent on three factors:<\/p>\n\n\n\n If any of these factors is absent, then disease cannot develop. Dollar Spot fungal disease is no exception to the disease triangle model (Figure 6).<\/p>\n\n\n\n We do need to take a fourth factor into consideration though, the factor of time. The longer the three factors in the disease triangle persist concurrently, the worse the disease outbreak is likely to be.<\/p>\n\n\n\n Leaf wetness is considered to be critical to the formation and spread of Dollar Spot. Not only does the causal fungusthrive in these conditions but also its dissemination by equipment, animals or people increases. Disease spread is greatly enhanced if an infected area of turf consistently supports heavy morning dews over a number of days.<\/p>\n\n\n\n Turf growing on dry soil is less able to take up essential nutrients and water from that soil. As such, an unhealthy sward is likely to occur within which plants become susceptible hosts that are more prone to fungal attack.<\/em><\/p>\n\n\n\n In compacted soils, the grass plant is less able to produce a deep and extensive root system, which would in turn contribute to forming a strong, resilient vegetative part of the plant. Turf growing in such compacted conditions can contain plants, which become a susceptible host to the causal fungus.<\/p>\n\n\n\n The stromata associated with Dollar Spot are believed to survive unfavourable conditions, mainly over winter, within the thatch layer. Turf growing where a significant thatch layer is present is therefore more likely to be able to support the stromata and contribute to the long-term activity of the disease. A site that is deficient in essential nutrients, especially nitrogen, is more prone to Dollar Spot attack and is much slower to recover from scarring. Without upward vegetative growth, infected leaves cannot be mown-off and taken away from the site.<\/p>\n\n\n\n An area of turf that lacks air movement across it is less likely to dry naturally at the canopy. This situation may be caused by being low lying or otherwise sheltered from the prevailing wind by geographical features or hedges, trees and buildings. Whatever causes impeded air movement or indeed the fact that the wind is still for a prolonged time; the natural drying process to the leaf is considerably compromised. A wet leaf is the perfect host to the causal fungus and is also more prone to promote its spread.<\/p>\n\n\n\n Likewise, an area affected by shade, especially from the early morning sun, is less likely to dry naturally. Again this problem may be caused by either vegetation or man made obstacle, whichever one it is, the fact that the leaf drying is impeded directly affects the likelihood of Dollar Spot outbreak and its dissemination.<\/p>\n\n\n\n Periods of prolonged high humidity also impact on the drying process to the leaf. Again these conditions would prolong leaf wetness with previously mentioned consequences to activity and spread.<\/p>\n\n\n\n It is also true to say that any damage to grass leaf tissue can make the plant far more susceptible. Such damage is often associated with blunt or badly adjusted mower blades that cause leaf tear thus exposing an open wound to infection.<\/p>\n\n\n\n Over the past two decades attacks have been noted in the UK from mid June to early October. It is during this period of the year that turf managers in many sports are under ever increasing pressure to produce the best quality swards possible. The scarring caused by a Dollar Spot attack is not only regrettable when considering the aesthetics of the playing surface but more importantly extremely damaging when taking into account the playability of such surfaces. Where individual Dollar Spot patches are seen to coalesce and affect a large area, the scarring can significantly affect the playability even more (Figure 7).<\/p>\n\n\n\n Residues left by fungicides that were used legally prior to their revocation may have also been controlling outbreaks of this disease, even if Dollar Spot wasn\u2019t on the label. Falling levels of these residues may have contributed to the increase in Dollar Spot.<\/p>\n\n\n\n A thorough understanding of the conditions that favour the outbreak of Dollar Spot is essential to be able to prevent attacks or predict when they might occur. Correct identification and an understanding of how the disease is likely to affect turf quality are crucial when planning the appropriate turf management.<\/p>\n\n\n\n Integrated Pest Management (IPM) programmes should now be the turf manager\u2019s standard approach to dealing with all turfgrass fungal diseases and Dollar Spot is no exception. An IPM approach will consider the following methods \u2013 cultural, mechanical, biological, genetic and chemical. One, some or all of these methods may be necessary but chemical control should always be considered as the last resort. <\/p>\n\n\n\n To culturally prevent or control Dollar Spot, sound management practices should be followed. These will promote a dense, durable, resilient and healthy sward less likely to contain plants that would be susceptible hosts to the fungus. If there is a history of Dollar Spot on a certain site, then these measures should be given more thorough consideration.<\/p>\n\n\n\n As duration of leaf wetness is such an issue when considering Dollar Spot, every effort should be made to reduce it to a minimum. Early morning dews should be removed by mowing, switching or brushing. When rainfall is insufficient, irrigation should be deep and infrequent, as light sprinklings using the \u201clittle and often\u201d approach often exacerbate the situation. Automatic irrigation should take place early in the morning rather than in the evening in order to reduce the time between water applications and physical dew removal. However, some sports turf managers have found that running light, overnight syringe cycles can assist in removing the, previously mentioned, guttation fluids from the leaf surface and in fact drying the leaf surface too to some extent.<\/p>\n\n\n\n Other ways of promoting the natural drying process include selective pruning and thinning of surrounding vegetation such as bushes, hedges and trees, thus allowing an increase in air movement and sunlight across the surface. Certain surfactant products have recommended rates of application purely to perform the function of dew removal. These may not have a long-lasting effect but could be useful during periods of high risk. Some sites are experimenting with brushes attached to robotic mowing equipment running on highly prone areas overnight to both manage dew build up and to disperse the sugar-rich guttation fluids.<\/p>\n\n\n\n![\"\"](\"https:\/\/aquatrolscompany.com\/wp-content\/uploads\/2025\/08\/blog-dollar-spots-Fig-1.webp\")
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