Dollar Spot is a widespread turfgrass disease that can quickly diminish the appearance of a healthy lawn. This fungal infection typically appears during periods of warm days and cool nights, especially when high humidity leads to prolonged leaf wetness. Understanding how to correctly identify the problem and implement targeted management strategies is the most effective approach to restoring and maintaining a dense, uniform turf. Addressing the outbreak involves immediate cultural adjustments, chemical treatments, and long-term improvements to the turfgrass environment.
Visual Identification of Dollar Spot
The most recognizable symptom of this disease is the appearance of small, circular patches of bleached or straw-colored grass. These spots are typically the size of a silver dollar or a quarter, measuring between one and three inches in diameter on residential lawns. On taller grass, these spots can merge to create larger, irregular blighted areas up to six inches across.
A closer look at individual grass blades reveals distinct lesions that help confirm the diagnosis. The lesions appear as light tan or straw-colored bands, often bordered by a dark reddish-brown margin. On longer blades, a characteristic “hourglass” lesion occurs where the tan spot girdles the leaf blade, narrowing the dead tissue in the middle.
Early in the morning, especially when dew is heavy, a fine, white, cobweb-like fungal growth, known as mycelium, may be visible across the affected patches. This growth is temporary and disappears as the sun dries the leaf surface, but its presence is a clear sign of active fungal growth. Recognizing these cues is important to distinguish Dollar Spot from other turf issues like drought stress or Brown Patch disease.
Modifying Cultural Practices for Control
Since the Dollar Spot fungus thrives in prolonged periods of leaf wetness and stressed turf, immediate adjustments to routine maintenance practices are the first step toward control. The duration of moisture on the grass blades allows the fungus to germinate and infect, making watering adjustments a foundational management technique.
Shifting irrigation to the early morning hours, between midnight and 6:00 a.m., significantly reduces the length of time the grass remains wet. Watering deeply and infrequently encourages deep root growth, helping the turf handle environmental stresses. Avoiding late afternoon or evening watering prevents the grass from staying saturated overnight, which favors disease spread.
The fungus is notably more severe in turfgrasses deficient in nitrogen, as this nutrient is necessary for the turf to generate new leaf tissue. A light application of a quick-release nitrogen fertilizer stimulates rapid turf growth, helping the grass recover more quickly than the disease can spread. This boost in nitrogen fertility helps the lawn repair damaged areas and increase its natural resistance.
Mowing practices also require modification, including maintaining the proper height for the specific turfgrass species to reduce stress. Avoiding mowing when the grass is wet prevents the mechanical spread of fungal mycelium and infected clippings to healthy areas. Removing morning dew by lightly dragging a hose or pole across the turf, or simply by mowing, can shorten the leaf wetness period and inhibit fungal activity.
When to Use Chemical Fungicides
While cultural practices resolve most minor Dollar Spot outbreaks, chemical fungicides may be necessary for severe or persistent infections, especially during peak disease pressure. Fungicides are most effective when applied preventively, but they can also be used curatively to halt an active infestation. Professional-grade products often contain active ingredients from classes such as Demethylation Inhibitors (DMI), like propiconazole, or Strobilurins (QoI), such as pyraclostrobin.
A major consideration when using chemical control is the risk of fungicide resistance, as the Dollar Spot pathogen develops resistance quickly. To prevent this, applicators must alternate between different fungicide classes with distinct modes of action, identified by their Fungicide Resistance Action Committee (FRAC) codes. For example, a DMI fungicide (Group 3) should be followed by a contact fungicide like chlorothalonil (Group M5) in the next application.
It is important to follow all label directions precisely, including the recommended application rate and interval, which can range from 7 to 28 days depending on the product and disease pressure. Applying the fungicide with adequate water volume, often two gallons per 1,000 square feet, ensures thorough coverage of the foliage where the fungus is active. Fungicides address the active pathogen, but they do not substitute for improving the underlying environmental conditions that allowed the disease to take hold.
Building Long-Term Turfgrass Resistance
Sustained control of Dollar Spot requires implementing long-term strategies that enhance the overall health and structure of the turf environment. Improving soil conditions is paramount, as a healthy root system directly correlates with the turf’s ability to tolerate stress and resist infection. Conducting a soil test provides data on nutrient levels, allowing for targeted application of elements like potassium and phosphorus, which contribute to plant vigor and stress tolerance.
Aeration and dethatching are mechanical practices that improve the environment by reducing excessive thatch buildup, where the fungus survives unfavorable conditions. Thatch, a layer of dead and living organic matter, can harbor the pathogen and impede water and nutrient movement into the soil. Regular aeration relieves soil compaction and improves air circulation, which reduces surface moisture and creates a less hospitable environment for the fungus.
Selecting turfgrass varieties that are genetically less susceptible to the disease offers the most durable form of resistance. When establishing a new lawn, choosing cultivars specifically bred for high Dollar Spot tolerance, often listed in university extension reports or National Turfgrass Evaluation Program (NTEP) data, provides a built-in defense mechanism. This integrated approach, combining cultural, chemical, and genetic strategies, is the most robust method for preventing future outbreaks.