The Dutch Golf Federation (NGF) has presented the results of a three-year study on integrated pest management (IPM) strategies against dollarspot. Targeted maintenance and smart prevention can effectively reduce the disease without leaning on the use of chemicals.
Dollar spot, caused by the fungus Clarireedia bennettii, is notorious for its erratic behaviour and direct impact on the playability of greens. The disease occurs worldwide and on every type of grass. The NGF was therefore very curious about methods that work on different types of greens.
In the field study, conducted between 2022 and 2024, 12 mutually different golf courses were visited 12 times each. This yielded 144 measurements. In each case, 22 parameters were measured, including soil moisture, grass cover, nutrient balance and disease activity.
“This is the first large-scale study in the Netherlands in which practical greenkeeping has been combined with scientific insights,” said project leader Arthur Wolleswinkel. “We have seen that certain ‘dials’ in maintenance such as preventive use of iron sulphate, rolling of greens and manual watering – actually contribute to suppressing dollar spot.”
Long list of conclusions
Based on the measurements, the three authors, Arthur Wolleswinkel, Gerard van ‘t Klooster and Casper Paulussen, come to a long list of conclusions:
There is no “one-shop stop solution”
The construction and history of the green are influential
Organic matter content in the top 2-4-6 cm should be kept above 3%
Frequent low doses of iron sulphate are suppressive
Applying iron sulphate after damage is counterproductive
Rolling works positively, provided the green is “compressible”
Smith-Kerns is a useful tool
Nitrogen “race to zero” is not beneficial for rough greens
Drought stress must be prevented
Duration of “leaf wet” has a direct relationship to the activity of dollar spot
Curative measures
According to Wolleswinkel, weekly application of 20 kg of iron sulphate per hectare, is most effective.
A striking outcome is the importance of preventive rather than curative measures. For instance, frequent iron sulphate application works better than occasional high doses afterwards. Bent grass-dominant greens also appear to be more susceptible to dollar spot than red fescue. This is partly because of longer leaf-netting time.
Although the dataset over three seasons does not yet allow for statistically firm conclusions, the study provides practical guidelines and recommendations for sustainable management.
According to the researchers, dew sprinkling can have a positive effect. They also do not consider the presence of felt to be a problem. It limits oxygen and buffers water and nutrients. In addition, they conclude that oxalic acid stimulates dollar spot. They therefore recommend further study on this.
Greenkeepers can now get started with specific profile sketches and generic management models (intensive, extensive, transition) drawn up on the basis of the 12 jobs studied. In doing so, the report provides not only insight but also action perspectives for the whole sector.