Dollar Spot is a common fungal disease of turfgrass caused by species within the genus Clarireedia. This disease affects nearly all turfgrass types, including bentgrass, bluegrass, and bermudagrass, leading to significant aesthetic damage. Identifying the visual signs of Dollar Spot is the first step toward effective management. The disease is typically most active during warm days and cool, moist nights, which encourage prolonged leaf wetness.
The Distinctive Patch Size and Shape
The most defining characteristic of Dollar Spot is the appearance of small, circular patches of damaged grass. These spots are often bleached, straw-colored, or light tan, contrasting sharply with the surrounding green turf. On closely mowed turf, such as golf greens, these spots are small and distinct, rarely exceeding one to two inches in diameter.
The disease earned its name because these small patches are roughly the size of a silver dollar. On taller grass, like residential lawns, the patches are slightly larger, ranging from two to six inches across. When the disease is severe, these individual circles multiply and merge, creating much larger, irregularly shaped areas of blighted turf.
Identifying Individual Leaf Lesions
Examining individual grass blades offers the definitive method for identification. Infected leaves first develop small, water-soaked spots that quickly dry out and turn a bleached tan or straw color. These lesions are typically found across the middle of the blade, not at the tip.
A specific and diagnostic symptom is the dark reddish-brown border that rings the tan lesion. On wider grass blades, the lesion often appears constricted, forming a distinctive “hourglass” or “dog-bone” shape. This shape occurs because the fungal infection girdles the leaf blade, causing the tissue to die on either side of the narrow center.
The combination of the straw-colored lesion, the dark border, and the hourglass shape on the individual blade is a reliable indicator. Observing these micro-symptoms requires close inspection of the grass blades at the edge of the affected patch.
Visual Clues and Look-Alikes
A temporary visual clue for active Dollar Spot infection is the presence of white, cottony growth, known as mycelium. This cobweb-like fungal growth may be seen spanning the affected grass blades in the early morning. The mycelium is most likely visible when there is heavy dew or high humidity, as it disappears quickly once the sun dries the grass.
The appearance of small, straw-colored patches can sometimes be confused with other diseases, such as Brown Patch. Brown Patch, caused by the fungus Rhizoctonia solani, forms much larger patches, often six inches to several feet in diameter, and may feature a dark, “smoky” ring at the outer edge.
Unlike Dollar Spot, Brown Patch does not produce the characteristic small, hourglass lesions on individual grass blades. The key to differentiation remains the individual leaf symptoms, as the overall patch size can vary significantly based on the grass type and mowing height. Looking for the distinct tan lesion with the dark reddish-brown border and hourglass shape will confirm the presence of Dollar Spot.