In Western Europe Dollar Spot disease of turf grass is being recorded with increasing incidence and severity. A disease that was once confined mainly to slender creeping red fescue grasses has in recent years become prevalent on most fine golf course grasses and has become a major disease problem in the summer months. Whilst still only minor in the UK, greenkeepers in central European Countries now rank it as a major summer problem. So why has it increased and what can we do about it?
Climate change and changes in the spread and severity turfgrass diseases has been reviewed and a good source of information on this can be found in a USA study published in 2017. The full text can be found here: –https://acsess.onlinelibrary.wiley.com/toc/14350645/2017/109/4
The authors make it clear that linking cause and effect is difficult, but it is reasonable to assume warmer climates with increasing humidity (turf under regular irrigation) will be predisposed to dollar spot attack.
There are many research papers and texts published on dollar spot ( for example Turfgrass Diseases: Dollar Spot (Causal fungus: Clarireedia jacksonii) (psu.edu) ) and the general factors that predispose the turf to attack are thought to be low fertility, warm weather, high humidity and presence of a susceptible host plant. Here is a review of what has been published on dollar spot control so far this year.
Fertilisation. As dollar spot is thought to occur more in low fertility conditions its increasing nutrients such as nitrogen, iron and sulphur may restrict disease development. We believe it is safe to say a balanced fertiliser programme, based on a soil/ leaf tissue chemical analysis and how the grass vigour appears is a good starting point. Iron sulphate has been recently studied in the laboratory and in field trials for dollar spot control, with mixed success. Whilst it may offer some suppression of the disease, it cannot be relied upon to give effective control. –Impact of ferrous sulphate concentration on Clarireedia isolate growth and dollar spot development – Shelton – 2021 – Crop Science – Wiley Online Library
Increasing nitrogen fertiliser applications may also suppress dollar spot, but as can be seen in this recent study, sometimes this needs to be done to excessive levels to get results. A big danger of course is sparking off Fusarium patch disease, which is often more damaging than dollar spot. – Dollar Spot Suppression on Creeping Bentgrass in Response to Repeated Foliar Nitrogen Applications | Plant Disease (apsnet.org) ; However organic amendments such as composts produced by earthworms have given good results. – Utilizing organic amendments for general suppression of dollar spot on creeping bentgrass turf – Beckley – – International Turfgrass Society Research Journal – Wiley Online Library . So, regarding fertilisation and dollar spot, balanced fertility with reliance on organic materials and careful use of nitrogen, and iron to mask the symptoms of dollar spot seems to be the most sensible practice.
There are effective fungicides for dollar spot and if used correctly can give good results in terms of less disease and increased turf quality. However, use of pesticides is restricted in many European Countries due to environmental concerns and they can be costly to use. – Efficacy of fungicide products for control of dollar spot on a USGA putting green (uoguelph.ca)
In both the USA and Europe bent grass cultivars have been screened for their resistance to dollar spot and choosing a resistant cultivar can help keep this disease at minimal levels. – The dollar spot susceptibility of 25 bentgrasses is consistent across five states in the Central USA. (cabdirect.org)
In summary, what can we do to from a practical viewpoint to prevent dollar spot happening in the first place and controlling outbreaks if they do occur. Here are our top 6 tips for success.
The first method is to control the microclimate around the grass leaf. Irrigate as little as possible and always use a wetting agent programme and spray dew dispersal/ mechanical removal to keep the turf surface as dry as possible. A managed application programme of wetting agent should be followed which involves monthly applications March- September with additional applications if there is severe water repellency.
The second method is to maintain a balanced fertiliser programme with no peaks or troughs in the major nutrients. An organic programme is ideal for this, and it can be supplemented with trace elements and potassium phosphite as required. Applying nitrogen will boost plant growth and make it less susceptible to dollar spot but it may also spark off Fusarium patch so there is a delicate balance between the two.
Thirdly, if possible use a resistant cultivar of bent grass. Cultivar choice is dependent on multiple factors but if dollar spot is a serious problem year after year this will be of great benefit.
Fourthly thatch control. Thatch contains a reservoir of the dollar spot fungus, so less fungal inoculum the less potential for disease.
Fifthly minimise plant stress using biostimulants. The less plant stress and the better rooted and overall health the plant is in the less prone to attack it will be.
Finally, fungicides have a place especially where disease is severe but do not over rely on them. Dollar spot will keep coming back if you do not tackle the underlying problems.
The final word is that if you are careful with plant nutrition and moisture management i.e., fertilise carefully with the right materials and keep irrigation to a minimum with the careful use of wetting agents the worst of dollar spot may be avoided