With ongoing hot, humid weather conditions, it’s important to be mindful of the symptoms of and triggers for Dollar Spot, as well as actions you can take to help mitigate this increasingly routine turfgrass disease.
Until recently, the disease was widely regarded as being a problem on fescue swards, especially slender creeping red fescue. However, significant damage can also occur on annual meadow-grass and bentgrass dominant turf.
In addition, Dollar Spot was initially thought to be a fairly low-level disease, but since the start of the millennium, outbreaks of Dollar Spot have become far more common, and the disease is now causing major problems for many turf managers looking after fine turf in Europe and the UK.
The possibility of infection increases when temperatures range from 15°C to 35°C with maximum risk seen when temperatures range between 25°C and 30°C and accompanied by humidity greater than 80% for a number of successive days. Risk is greater with increasing relative humidity, temperature, and moisture. A wet leaf is the perfect host for the causal fungus and is also more likely to result in the spread of the disease.
What Does Dollar Spot Look Like?
Classic symptoms are small bleached, straw-coloured spots normally no bigger than 50 mm in diameter, the size of an old silver dollar coin. Disease activity can occur rapidly, and spots appear as sunken areas that may coalesce to give larger areas of damage. Unlike other common turf grass diseases, it is unusual for the individual spots to dramatically increase in size.
If conditions change following the initial infection, nights become colder and drier, or control measures are implemented quickly and successfully, the infection may not become more severe than scattered leaf lesions. If combined with vigorous growth, the damage may quickly be mown out.
However, if favourable conditions persist following infection, with warm nights and heavy dews, and if control measures prove to be unsuccessful, severe leaf blade damage may occur, and the characteristic spots may appear on the turf. As this disease activity typically coincides with the peak of the summer competition season, damage can cause disruption to golf, from both aesthetic and playing quality perspectives.
When hot days and warm nights, together with high humidity, are experienced, dense aerial mycelium may also be seen on the affected turf blades early in the morning.
Typical Dollar Spot Symptoms on a Golf Green
Dense Aerial Mycelium on Affected Leaf Blades
What Can You Do?
In The Short Term
- Keep the leaf and turf surface as dry as possible by removing atmospheric dew and plant guttation during periods of high disease risk. Mow, switch or brush surfaces early each morning.
- Avoid late-evening irrigation. Irrigation should take place early in the morning to reduce the time between water applications and subsequent dew removal.
- Consider using dew removal products during high-risk periods, although effectiveness is short-lived under strong growth and frequent mowing.
- Avoid light, frequent irrigation practices, aiming instead for heavier, less frequent irrigation if storage systems allow.
- Box off clippings from affected areas if not already doing so.
- Ensure mower blades are sharp to reduce wounding to the leaf when mowing.
- Ensure good moisture balance within the rootzone to reduce plant stress.
- Avoid excessively low nitrogen levels; higher nitrogen levels may be required to reduce the risk of disease.
- The application of iron sulphate may be beneficial during periods of low to moderate disease pressure by changing the environmental conditions making them less suited to the pathogen.
- If there is a history of Dollar Spot activity, applications of fungicide during high-risk periods can be guided by disease predictive models such as the Smith‐Kerns Dollar Spot Model | Turfgrass Diagnostic Lab (wisc.edu). This Excel spreadsheet allows turf managers to track a 5-day moving average of daily relative humidity and daily average air temperature to create a probability that Dollar Spot will occur on a given day. Note that fungicide resistance is important, this disease has proven tolerant to SDHI fungicide chemistries in certain parts of the world such as Asia and USA. Chemical control should always be considered as the last resort.
In The Longer Term
- Maintain good control of organic matter to reduce opportunities for overwintering of the disease.
- Prune or thin surrounding vegetation, increasing levels of air movement and sunlight to improve the growing environment.
- Introduce more genetically disease-tolerant turfgrass species.
- Biological controls are likely to form an integral part of management in the future as reliance upon synthetic plant protection products reduces.
In conclusion, Dollar Spot appears to be on the increase and could possibly become a more widespread problem for managers of fine turf across the UK and Europe as climates change and hotter, drier summers are accompanied by warmer, wetter winters. If the current trend continues, more research is required to determine better prevention and control strategies.
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