Causal fungus: Sclerotinia homoeocarpa, recently renamed as Clarireedia jacksonii
Host Grass: Highly managed cool-season turfgrasses such as bentgrass and annual bluegrass are the most susceptible. Warm-season turfgrasses can be infected by dollar spot, but highly managed bermudagrasses and zoysiagrass are more susceptible.
Cause and Symptoms:
Dollar spot occurs from late spring through fall and is most active during warm and humid days (70 to 85oF) and cool nights (60oF) which leads to heavy dew formation. Early symptoms on fine textured and close-cut turf include round, sunken patches of bleached-out or straw-colored grass which measure 1-2 inches in diameter, the size of a silver dollar (Figure 1). As the disease progresses, spot sizes grow until they meet with adjacent spots to form bigger, irregularly shaped patches. In coarse textured or high-cut turf, the symptomatic spots are larger and more diffuse. This leads to dollar spot being confused with other diseases such as brown patch (caused by Rhizoctonia solani), another common fungal infection in cool-season turfgrasses during the summer.
Characteristic symptoms for dollar spot on leaf blades are white to tan leaf spots with a dark brown margin at the beginning of the infection; these leaf spots later cover the width of the leaf, taking on an hourglass shape (Figure 2). When the disease is active, cobweb-like mycelium can be seen growing on affected leaves early in the morning before dew dries.
Control and Management: Key cultural practices that reduce the occurrence and severity of the disease include the following:
- Aerate soils to reduce compaction and remove thatch.
- Remove morning dew by poling, irrigating or mowing.
- Allow consistent air flow in the area by pruning or removing shrubs or trees as needed.
- Water grass during early morning hours to reduce the time that leaf blades are wet.
- Maintain proper fertility and adequate soil moisture.
Proper thatch management is important for controlling dollar spot. Excess thatch can be removed by vertical mowing or aerification with hollow tines. Make sure to properly dispose of clippings, once removed or collected from an infected area. Infected plant materials are a primary source of new outbreaks. For the same reason, make sure all equipment used in an infected area – including mowers and other turf-maintaining equipment and tools – is thoroughly cleaned before using it in other non-infected sites. Regular amounts of nitrogen fertility will help damaged turf to recover from this disease. Maintaining adequate soil moisture is important for dollar spot management since drought stress increases disease severity.
The best preventative approach is to choose a less susceptible turfgrass. For example, dollar spot seldom makes significant damages on St. Augustinegrass or centipedegrass. Fungicide applications are critical for highly managed turf such as golf courses and professional sport fields during conducive weather conditions.
Content edited by:
Young-Ki Jo (email@example.com, Professor and Extension Specialist)
Raleigh Darnell and Paul Goetze (Extension Assistant)
Department of Plant Pathology & Microbiology, Texas A&M AgriLife Extension Service
September 31, 2021