Dollar Spot is a widespread turfgrass disease that can significantly diminish the quality of your lawn, affecting many common grass species. This fungal infection, primarily caused by species of Clarireedia, is considered one of the most common and costly turf diseases to manage. The disease is most active when warm, humid days are followed by cool nights, which results in prolonged periods of leaf wetness. Understanding the visual cues of this pathogen is the first step toward effective treatment and maintaining a healthy, uniform turf surface.
Identifying Dollar Spot
The most recognizable symptom is the appearance of small, circular, sunken patches of straw-colored grass. On closely mowed turf, these spots are typically the size of a silver dollar (1 to 3 inches in diameter), which gives the disease its name. In taller residential lawns, these affected areas can expand into larger, irregular patches up to 6 inches across. The causal agent, Clarireedia jacksonii, attacks the leaf tissue without killing the grass roots or crowns.
A closer inspection of individual grass blades confirms the diagnosis by revealing characteristic lesions. These lesions are light tan with a distinct reddish-brown border, often constricting the leaf blade into a unique hourglass or ‘dog-bone’ shape. The presence of white, cobweb-like fungal threads, known as mycelium, is another strong indicator, especially when observed early in the morning when the turf is covered in dew. Dollar Spot is favored by low nitrogen fertility, excessive thatch buildup, and at least 10 to 12 continuous hours of leaf wetness.
Cultural Practices for Management
Managing the environmental conditions of the turf is the most effective long-term strategy for suppressing Dollar Spot activity. The primary goal is to reduce the duration of leaf wetness, which is necessary for the fungus to initiate infection. Adjusting irrigation schedules to water deeply and infrequently, ideally between midnight and 6 a.m., allows the foliage to dry quickly with the morning sun. Removing morning dew by lightly dragging a hose or rope across the lawn, or simply mowing, can also physically dislodge the moisture and disrupt the fungal growth cycle.
The nutritional status of the lawn plays a major role in its susceptibility, as the disease thrives in low-nitrogen environments. Implementing a balanced fertility program that ensures adequate nitrogen levels throughout the growing season is important for prevention and recovery. A slow-release nitrogen fertilizer can stimulate consistent, moderate growth, allowing the turf to rapidly grow out of the leaf spots and repair damaged areas. Applying a small amount of nitrogen in the late spring can help minimize disease severity when infections typically begin.
Maintaining proper lawn height and managing organic matter helps create an unfavorable environment for the pathogen. Mowing at the higher end of the recommended range for your grass type, typically 2 to 3 inches for common lawn grasses, promotes turf health and vigor. Thatch, the layer of organic matter between the grass blades and the soil surface, can harbor the fungus, so periodic aeration or vertical mowing to reduce excessive buildup is beneficial. Pruning surrounding trees or shrubs to improve air circulation and increase sunlight penetration helps dry the turf canopy more quickly.
Selecting and Applying Fungicides
When cultural methods prove insufficient or disease pressure is high, chemical intervention with fungicides may be necessary. Fungicide products are categorized into two types: contact and systemic, which differ in how they interact with the fungus and the plant. Contact fungicides, like chlorothalonil, remain on the leaf surface and provide a protective barrier against new infections, requiring more frequent reapplication.
Systemic fungicides, such as those containing propiconazole or thiophanate-methyl, are absorbed by the grass and move within the plant tissue, offering longer-lasting control. These products are used for curative treatment or in a preventative program when environmental conditions are conducive to disease development. For maximum effectiveness, fungicides should be applied preventatively, before or at the first sign of the disease, rather than waiting for significant damage.
Chemical control requires rotating fungicide classes to prevent the development of resistance in the Clarireedia population. Fungicides are assigned a Fungicide Resistance Action Committee (FRAC) code based on their mode of action, and it is important to alternate between products with different codes. Rotating a multi-site contact fungicide with a systemic Demethylation Inhibitor (DMI) fungicide, like propiconazole, is a common resistance management strategy. Following the specific application rates and intervals listed on the product label is necessary for both safety and achieving optimal disease control.