Exploring the impact of dollar spot on golf courses

Dollar spot is a relatively new disease to the UK and in 2023 we saw the largest outbreak we have seen on our shores. Previous outbreaks had been restricted to the Channel Islands and Southern UK, however due to the high humidity experienced in the UK in 2023 we observed outbreaks as far North as Aberdeen. In the USA this is considered the most detrimental disease to Golf Courses, as it is a summer disease that can severely affect surface aesthetics as well as surface performance. At the time of year that golfers expect perfection, and firm, true and smooth surfaces, we observe tanned pitted spots all over the green.

Symptoms

Tanned spots about the size of a Dollar coin (Dollar Spot!) around 2-5cm in diameter. Usually appear on highly managed turf such as tees, fairways, approaches, and greens. On close inspection, hourglass shaped lesions can be seen on the leaf blade. Spots can typically coalesce which can wipe out large areas of turf.

This is a fungal disease which is spread through small bits of mycelium moving to a new plant host. They move in water and can also be spread on shoes, golf equipment and turf management equipment. This disease does not produce spores but scientific experts in the states believe that this disease could be entering the seedling of the plant and spreading as the seed drops.

Environmental conditions

If environmental conditions are conducive to the disease requirements an outbreak could be imminent. Temperature can range between 12-32oc with an 80% relative humidity. Leaf wetness, low fertility, susceptible grass species, and leaf and surface wetness can also encourage the disease activity. Collecting weather data is important for preventative monitoring of Dollar Spot.

Disease model – Smith-Kerns Dollar Spot Model

The widely used Dollar Spot Model uses a 5day rolling average of relative humidity and average air temperature to give the probability of a disease outbreak. If the risk reaches 20% probability a preventative IPM programme is recommended to prevent disease. It is important to use forecasted weather data to plan. If probability is above 20% and increasing for the 7 days ahead, implement your IPM strategy. Relative humidity is heavily weighted in this model as we can see in the diagram below. Temperature can be as low as 12-15oc but if relative humidity is 100% the probability of Dollar Spot is 40%.

Management strategy

Origin Amenity Solutions (OAS) can provide advice and strategies based on cultural practices that can help support dollar spot management. Points to consider include over seeding with grass species and cultivars that are less susceptible to Dollar Spot. Some fescue, bent and creeping bent species are excellent for Dollar spot resistance.

Studies in the States on creeping bent grasses shows a decrease in Dollar Spot from rolling greens. A 61% decrease when rolling twice per week and 95% decrease from four times per week. Rolling is only recommended when conditions are conducive.

Dollar Spot is a foliar disease so maintaining sharp blades on all maintenance equipment will reduce damage to the leaf tissue and minimise sites for the fungus to enter the leaf tissue.
Dollar Spot is often associated with low fertility. Collecting clip volume data can be an extremely useful data set when planning your nutritional inputs and collecting this alongside Growth Potential (20oc) will give you Growth Ratio data.

As with most diseases moisture management is key to reducing the possibility of an outbreak.

· Irrigation cycles should run in the early hours of the morning rather than in the evening to avoid prolonged leaf wetness, or short irrigation application during the night to break leaf wetness duration if a dew forms early evening.

· Irrigate to depth to ensure good soil moisture management, monitoring evapotranspiration rates to avoid moisture deficit. This will reduce surface moisture and encourage root development for a healthier plant.

· Remove dew as early as possible and rotate cutting regime, so you don’t remove dew from the last green every time you cut.

· Use wetting agents to reduce surface tension and allow water to penetrate into the soil profile more efficiently. Water will spread through the profile to produce a consistent moisture level.

There have been some in vitro trials indicating, but not conclusive, that encouraging an alkaline pH on the leaf surface can lead to a natural suppression of Dollar Spot. Using the principles of the OAS 20/20/30 strategy, but with more alkaline constituents, progress is being made in the field to support your Dollar Spot IPM Plan. Ask us for more information.

Exteris Stressgard is an excellent fungicide for Dollar Spot prevention. In addition, Stressgard is a proven technology that mitigates stress and maintains plant health to improve consistency in turf quality, therefore delivering great playing surfaces. Exteris Stressgard delivers immediate aesthetic improvements and long-term plant health benefits proven with Stressgard technology.

by Kelly-Marie Clack, Agronomy Technical Manager – Origin Amenity Solutions.