Dollar Spot

Dollar spot, caused by the fungus Clarireedia jacksonii, is a prevalent turf disease affecting highly managed turf areas worldwide. This disease is identifiable by its small, round, bleached spots, typically 1-3 inches in diameter on closely mowed turf such as golf courses. In higher mown turf, these spots can grow to about 6 inches across. A key characteristic of an active infection is the presence of a white, cottony growth of fungal mycelium when dew is present.

The fungus survives in infected plants or as stromata on leaf surfaces during unfavorable conditions. The disease thrives at temperatures between 60-90 °F, commonly occurring when days are warm, nights are cool, and heavy dew is present. Dollar spot is most active from mid-May through mid-October and is more severe in dry soils with low nitrogen fertility.

Cultural Management Strategies

1. Watering Practices: Water deeply and infrequently to avoid moisture stress.
2. Dew Removal: Use techniques like mowing, rolling, whipping, or poling greens early in the morning to remove dew and guttation fluids.
3. Nitrogen Fertility: Maintain adequate to high nitrogen levels in the soil through light, frequent fertilization, which helps reduce disease severity and promotes recovery.
4. Pruning for Air Circulation: Prune trees and shrubs to improve air circulation and promote rapid drying of the turf, reducing the likelihood of fungal growth.
5. Turf Selection: Overseed with newer, less susceptible turf cultivars to reduce the impact of Dollar spot.
6. Rolling: Implement a program of lightweight rolling on golf greens to help suppress the disease.
7. Organic and Biological Controls: Utilize organic fertilizers, composts, and biofungicides as part of an integrated pest management strategy.

Chemical Management and Resistance

Fungicide resistance has been an issue for over forty years, particularly where applications are frequent, as on golf courses. Resistance has been reported in several systemic fungicide groups including sterol biosynthesis inhibitors (DMIs), dicarboximides, and benzimidazoles (thiophanate-methyl). To mitigate resistance development, follow these guidelines:

1. Follow Label Directions: Always adhere to the manufacturer’s instructions when applying fungicides.
2. Preventative Applications: Apply fungicides preventatively during periods of high disease pressure.
3. Rotation of Active Ingredients: Avoid repeated use of fungicides from the same class or FRAC code. Instead, rotate or mix fungicides with different modes of action.
4. Integrate Cultural Practices: Maximize cultural practices to reduce the dependency on fungicides.

Preventive Measures and Monitoring

1. Regular Monitoring: Regularly inspect turf for early signs of Dollar spot to enable timely intervention.
2. Soil Testing: Conduct soil tests to ensure optimal nutrient balance and pH levels, which can enhance turf resilience.
3. Environmental Management: Manage environmental conditions, such as shade and humidity, to create less favorable conditions for fungal growth