Dollar spot is one of the most common and visually distinct diseases affecting turfgrass, capable of transforming a lush green lawn into a patchwork of straw-colored spots overnight. Caused by the fungal pathogen Sclerotinia homoeocarpa, this disease targets the leaf blades rather than the roots, making it more of a cosmetic nuisance than a direct killer of the plant crown. Understanding how to identify dollar spot is the critical first step in managing its appearance and preventing it from spreading across your property.
Initial Visual Symptoms
In the early stages, dollar spot presents as small, circular patches that are easy to overlook. These spots typically start as water-soaked areas that quickly fade to a light tan or bleached yellow color. The affected blades appear wilted and collapse, creating a texture that looks distinctly different from the firm, upright grass surrounding it. Because these initial symptoms can mimic drought stress or morning dew burn, close inspection is necessary to confirm the diagnosis.
Distinctive Leaf Lesions
The most reliable method for identifying dollar spot is examining the individual grass blades within the affected area. Look for small, distinct lesions that appear midway up the leaf blade. These lesions have a characteristic appearance: they are usually straw-colored or tan with a reddish-brown or purple border running along the edges. If you run your fingers against the grain of the blade, these borders often feel rough or water-soaked, providing a tactile confirmation of the disease.
As the disease progresses, the lesions expand until they eventually girdle the entire blade. When this happens, the blade will dry out and turn completely white or bleached, while the base of the plant, known as the crown, often remains dark green and healthy. This contrast between the healthy crown and the dead, white tip of the blade creates a "two-tone" or mottled appearance that is a hallmark of advanced dollar spot.
Pattern Formation and Size
While the individual spots caused by Sclerotinia homoeocarpa are often small, they have a tendency to merge together as the humidity rises and the disease spreads. When multiple spots grow and converge, they form larger, irregularly shaped dead zones that can range from the size of a dinner plate to the size of a basketball backboard. In high humidity conditions, you might observe a distinct "smoke ring" of mycelial webbing—a fuzzy, cobweb-like substance—around the perimeter of the damaged area during the early morning.
Common Misidentifications
Because dollar spot thrives in similar conditions as other turf diseases, it is frequently confused with other ailments. Unlike brown patch, which creates large, circular areas of tan grass with dark brown edges, dollar spot lesions are much more defined and uniform in shape. It is also distinct from fairy ring, which typically forms perfect circles with dark green grass and mushrooms, whereas dollar spot spots appear as random, scattered patches of tan rather than geometric rings.
Environmental factors can sometimes mimic the visual symptoms of dollar spot. Low nitrogen fertility, drought stress, or physical damage from heavy equipment can cause similar yellowing or browning of the turf. However, the key differentiator is the specific pattern of the lesions on the leaf blade; if the blades are uniformly yellowed without the distinct tan lesions and purple borders, the issue is likely cultural rather than fungal.
Favorable Conditions and Prevention
Dollar spot is most prevalent during the warm months of late spring through summer, but it can also appear in the fall when humidity remains high. The disease spreads most aggressively when nighttime temperatures are between 50 and 70 degrees Fahrenheit and when the grass remains wet for extended periods due to dew, rain, or improper irrigation. Lawns that are mowed too short or lacking in nitrogen nutrition are particularly susceptible, as the stress weakens the plant's natural defenses.
