Dollar Spot: how to fight?

Dollar Spot is one of the most widespread and destructive fungal diseases, especially on golf courses and ornamental turfgrasses. It is caused by a pathogenic fungus that causes visible damage in the form of discolored spots that weaken the turfgrass. Due to its aesthetic and structural impact, this disease requires specific management measures to preserve the quality of green spaces, particularly those intended for intensive use.

What is Dollar Spot?

Dollar Spot is a common fungal disease of ornamental turf, golf courses, and sports turf. Also known as dollar spot or summer sclerotinia , this disease is caused by the fungus Sclerotinia homoeocarpa , recently reclassified in the genus Clarireedia sp . 

Several species in this genus are involved in the development of Dollar Spot, but Clarireedia jacksonii predominates in cool-season grasses such as bentgrass, red fescue, and Kentucky bluegrass. Some rarer species, such as Clarireedia monteithiana , Clarireedia homoeocarpa , and Clarireedia bennettii , are also associated with this disease.

Which host plants are affected?

Dollar Spot thrives primarily on certain grasses, particularly those found on well-maintained, regularly mown terrains, such as golf courses. Commonly affected grasses include:

• Red fescue ( Festuca rubra )
• Annual bluegrass ( Poa annua )
• Creeping bentgrass ( Agrostis stolonifera )
• Kentucky bluegrass ( Poa pratensis )
• English ryegrass ( Lolium perenne )

What are the conditions for the development of the spot dollar?

Dollar Spot develops mainly between spring and fall , when grasses are in full growth. The disease becomes visible as early as early May or April and can persist until November. 

The fungus thrives when daytime temperatures are high (between 20 and 30 °C), combined with cool nights that promote the formation of dew . This combination of temperatures, combined with high humidity around 80%, creates an environment that is particularly conducive to its development. 

Stagnant humidity , reinforced by the presence of night dew and the lack of ventilation in certain areas, further increases the risks of infection. 

Finally, let us emphasize that lawns stressed and weakened by drought, nutrient deficiencies such as phosphorus and potassium, or excess nitrogen are all the more vulnerable to this disease.

What are the symptoms of the dollar spot?

Dollar Spot is first observed as small, round, discolored spots that measure between 3 and 7 cm in diameter, which appear on the lawn. These spots, which are pale yellow , can gradually spread and merge to form larger areas, leaving bare patches on the lawn. 

In case of high humidity or dew, a whitish mycelium , reminiscent of a spider web, may appear around infected blades of grass, making it easier to identify the disease. 

Damage is particularly visible when the lawn is cut very short , a factor that makes symptoms more pronounced, especially on golf courses and other lawns maintained at low cutting heights.

How does the spot dollar spread?

Dollar Spot spreads through mycelium, which can be carried from one infected area to another by gardening tools, shoes, wind, or animals . This spread facilitates the colonization of new lawn areas, making it necessary to take precautions when maintaining the lawn.

How to prevent the dollar spot?

To effectively combat the Dollar Spot, several preventive measures can be put in place:

• Aeration : Improving soil aeration helps reduce thatch and increase air circulation, creating an environment less favourable to fungal development (we recommend the application of Siliboost and Soufrel).
• Watering management : adapting watering by making it regular and moderate avoids water stress without promoting excessive humidity. Watering at the end of the night or early in the morning is ideal for limiting stagnant humidity.
• Nutrition : Adding potassium at the beginning of summer strengthens grasses, making them less susceptible to infections. This nutrient supply helps maintain vigorous and resistant lawns (we recommend applying the biostimulant Yakadop).
• Mowing height : Increasing mowing height reduces the visual impact of fungal spots. This helps maintain more even coverage and reduces stress on plants.
• Sowing suitable varieties : choosing dense lawn varieties that tolerate trampling, are disease resistant and require little treatment to reduce the risk of disease spreading.
• Use of biostimulants : the application of biostimulants stimulates the natural defenses of grasses, to strengthen their resilience against Dollar Spot.

Agrobiotop solutions against the dollar spot

For soil aeration (action on felting)

For the nutrition of golf courses and sports fields:

Treatments for Dollar Spot Disease :