Technical
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’t on the label
Figure 7. The affect of concentrated humus applications on Dollar Spot incidence (Virginia Tech‐1997)
exception. An IPM approach will consider the following methods ‐ 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.
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. As duration of leaf wetness is such an issue when considering Dollar Spot, every effort should be made to reduce it to a minimum. Removal of early morning dews by mowing, switching or brushing should be considered. When rainfall is insufficient, irrigation should be deep and infrequent, as light sprinklings using the “little and often” 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. Following a programmed approach using proven surfactant technology can assist with the function of dew removal as well as addressing issues associated with soil dryness. Deep, infrequent irrigation, in conjunction with the application of the correct water management technology, will maintain uniform moisture levels in the soil profile. This will enable the plant to take up water plus essential nutrients that will, in turn, increase plant health, limit plant stress and make the sward less prone to attack. Every effort should be made to maintain an open, well‐aerated and non‐compacted profile. Regular aeration using different tines at varying depths will result in a healthy rootzone within which a vigorous sward can survive. All operations should take place when soil conditions are consistent with those required to ensure the desired results. Management of any thatch layer is
paramount in the prevention and the control of Dollar Spot. Although correct aeration operations will help to ensure an environment where beneficial micro‐organisms can aid in the breakdown of thatch, its mechanical removal is often necessary. Regular verti‐ cutting can prevent its build up, whilst deeper scarification operations remove lower lying thatch layers. The control of both the depth and density of any thatch layer will not only promote a healthier sward, but will also limit the available environment needed by the stromata associated with Dollar Spot to survive unfavourable conditions for disease activity. A balanced nutrient input should be adhered to with adequate nitrogen applications being key. A sward that is growing will not only facilitate the removal of infected blades in boxed‐off grass clippings, but will also ensure quicker recovery from an outbreak. Mowing practices are also considered to be key in the management of this disease. Firstly, it is essential that mower blades are sharp and give a clean cut to the leaf blades as these wounds soon heal over. Such wounds are far less readily infected by mycelium. Secondly, it is good practice to box‐off clippings from an infected area and dispose of them accordingly. Letting infected clippings fly in this situation only serves to spread the disease further. The use of Dollar Spot resistant cultivars should be considered when carrying out overseeding to a previously infected area, or indeed when seeding or turfing a new area on a site that has a history of outbreaks. Certain cultivars of Agrostis stolonifera (creeping bentgrass), namely L‐93, A‐1, Providence and Pennlinks have shown superior tolerance to Dollar Spot in the US (Hurley, 1999).
Ongoing trials work
Although the exact mechanism of suppression is not fully understood, there has been research in the US to suggest that certain commercially available organic fertilisers have given some degree of control of Dollar Spot (Liu et al.,1995; Nelson and Craft, 1991). The results from the 1997 study at Virginia
Tech suggest that applications of concentrated humus can reduce Dollar Spot outbreaks (Figure 7). They suggest that the concentrated humus created a more favourable environment for plant growth, that it strengthened the plant’s natural defences and that it possibly promoted the growth of beneficial fungi and bacterial species in the soil that could discourage the pathogen through competition. Aquatrols research trials will be looking to emulate this work with our recently launched range of products containing Aquavita technology with regards to the control of Dollar Spot as the disease raises its profile in the UK. As with most aspects of turf grass management, a pro‐active approach is always the best practice. In the case of Dollar Spot, both the formulation as well as the implementation of an IPM programme is crucial to the prevention and control of this disease. There are many options, be they cultural, mechanical, biological or genetic, before the need to apply a chemical control. In conclusion, Dollar Spot appears to be on the increase and could possibly become a widespread problem for managers of fine turf across the UK. If this proves to be correct, it is certain that much more research will be carried out into the causal fungi as well as both prevention and control strategies.
”
Michael Fance, Technical Support Manager, Aquatrols Europe Ltd
PC JUNE/JULY 2018 I 127
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