Bermuda grass is a warm-season turf known for its resilience and ability to thrive in hot climates. However, even this aggressive turf is susceptible to stress, and the appearance of black spots is a common visual sign that a fungal pathogen has taken hold. These spots are not a disease themselves but rather a symptom, indicating an underlying fungal infection that flourishes when specific environmental and management conditions align. Recognizing the difference between the primary fungal culprits is the first step toward effective treatment and long-term prevention.
Primary Fungal Diseases Causing Black Spots
The most frequent cause of black spots on Bermuda grass is Leaf Spot, a condition broadly attributed to species of Bipolaris or Drechslera. This disease was often referred to by the older classification, Helminthosporium. Initial symptoms appear as small, dark purple or black flecks on the leaf blades and stems.
These lesions expand into distinct, elliptical spots that feature a tan or bleached center surrounded by a dark reddish-brown or purple border, creating a characteristic “eye spot” appearance. Under prolonged wet conditions, these spots merge, causing the entire leaf blade to wither and die back, a severe stage sometimes called “melting out.” The pathogen can then progress to the crown and roots, leading to turf thinning and large, irregular blighted areas.
Another disease that can present with dark borders is Dollar Spot, caused by the fungus Clarireedia jacksonii. While the spots themselves are typically straw-colored or light tan, the individual lesions on the grass blades exhibit a bleached center bounded by a distinct reddish-brown or black margin. Dollar Spot attacks only the leaf blades, resulting in small, circular, depressed patches roughly the size of a silver dollar on closely mown turf. When the disease is active, a fine, white, cobweb-like fungal growth, or mycelium, may be visible across the affected patches.
Management Errors That Trigger Outbreaks
Fungal diseases require a susceptible host, a pathogen, and an environment conducive to disease growth. The most common trigger for black spot outbreaks is a series of management errors that create a moist and stressed environment.
Improper watering is a significant contributing factor, particularly frequent, shallow irrigation. This keeps the leaf blades wet for extended periods, providing the moisture necessary for fungal spores to germinate and infect the plant tissue. Watering late in the day or evening compounds this issue, as the grass remains wet overnight, significantly increasing the duration of leaf wetness required for most fungal diseases to thrive.
Mowing practices also play a large role in turf stress and susceptibility. Cutting the grass too low, or “scalping,” physically injures the plant, weakening its defenses and creating open wounds for pathogens to enter. Using a dull mower blade tears the grass instead of cleanly cutting it, stressing the plant and leaving frayed edges highly susceptible to infection.
Nutrient balance is another element, as both deficiencies and excesses can predispose the turf to disease. Dollar Spot is often exacerbated by a lack of nitrogen, while Leaf Spot can be triggered by the opposite: an excessive application of nitrogen fertilizer. Too much nitrogen promotes rapid, weak, succulent growth that is vulnerable to the Leaf Spot pathogens. Additionally, a thick layer of thatch—the accumulation of organic material between the soil and the grass blades—provides a reservoir for the fungal mycelium to survive and spread.
Curing and Preventing Future Spots
The initial step in managing black spot diseases is to immediately correct the cultural practices that created the favorable environment. Adjust your watering schedule to apply water deeply and infrequently, preferably in the morning before 10 a.m. This timing allows the leaf blades to dry completely throughout the day, minimizing continuous leaf wetness.
Next, address the mowing routine by raising the cutting height to reduce stress on the grass. Ensure the mower blade is kept sharp to produce a clean cut, promoting faster healing and reducing infection entry points. Collecting and removing grass clippings when the disease is active can also help prevent the spread of fungal spores across the lawn.
For severe or persistent outbreaks, a chemical treatment may be necessary to cure the existing infection. Fungicides containing active ingredients such as propiconazole or azoxystrobin are commonly used. When applying, follow the manufacturer’s directions precisely, using the higher, curative rate. Rotating between different chemical classes is necessary to prevent the fungi from developing resistance.
Long-term prevention focuses on improving the overall health and resilience of the Bermuda grass. Annual aeration helps alleviate soil compaction and improves water infiltration and air circulation, leading to a healthier root system. Dethatching is also important to manage the organic layer where fungal pathogens survive. Performing a soil test and maintaining a balanced nutrient program, especially avoiding excessive nitrogen, will strengthen the turf against future outbreaks.