Bermuda grass is a resilient, vibrant warm-season turf popular for lawns and sports fields. However, black spots can appear, detracting from its aesthetic appeal and signaling underlying problems that require attention for a healthy lawn.
Identifying Black Spots
Black spots on Bermuda grass manifest in various ways, providing clues about the underlying cause. They can appear as small, irregular dark specks on individual blades, sometimes purplish or brownish-black. These spots may expand into larger lesions with a tan or bleached center and a dark border. Discoloration can also be a powdery or slimy coating, or larger, darkened patches across the lawn. Affected areas range from isolated spots to widespread patterns, sometimes giving the turf a thinned or scorched appearance.
Common Causes of Black Spots
Black spots on Bermuda grass are typically symptoms of fungal diseases, pest activity, or unfavorable environmental conditions.
Fungal Diseases
Several fungal pathogens cause black spots. Leaf spot, primarily caused by Bipolaris species, presents as purplish-black spots with tan centers on individual blades. These lesions can coalesce, leading to thinning or “melting out” of the turf, thriving in cool, wet periods. Gray leaf spot, caused by Pyricularia grisea, appears as brownish-black, diamond-shaped lesions, often with a yellow halo, causing blades to shrivel and die. This fungus is common in warm, humid conditions. Brown patch, caused by Rhizoctonia solani, primarily creates circular brown patches, but can also cause dark or smoky edges during warm, humid conditions. Slime mold, a superficial fungal growth, appears powdery or slimy on grass blades after heavy rain or in humid conditions. It is unsightly but does not directly harm the grass.
Sooty Mold
Sooty mold is a black, powdery coating on grass, not a direct disease. It grows on honeydew, a sticky substance excreted by sap-sucking insects like aphids, scale, or mealybugs. Sooty mold indicates an underlying pest infestation. While primarily cosmetic, severe cases can block sunlight, limiting photosynthesis.
Environmental Factors
Certain environmental conditions promote fungal growth. Excessive moisture from overwatering or poor drainage leads to prolonged leaf wetness, ideal for many fungal pathogens. High humidity, especially with warm temperatures, also promotes disease. Compacted soil hinders water infiltration and air circulation, stressing the grass and increasing disease susceptibility.
Cultural Practices
Improper lawn care practices weaken Bermuda grass, increasing vulnerability to black spots. Mowing too low (scalping) stresses the plant and increases disease susceptibility. Over-fertilization, particularly with excessive nitrogen, leads to lush growth prone to fungal infections. Inconsistent watering, especially shallow and frequent irrigation, encourages shallow root growth, reducing vigor and disease resistance.
Treating Black Spots
Addressing black spots involves cultural adjustments and, in some cases, targeted treatments.
Cultural Controls
Adjusting watering practices is a primary step. Water deeply and infrequently, aiming for 1 to 1.5 inches per week. Water in the early morning to allow blades to dry before nightfall, reducing leaf wetness that fungi favor. Maintain proper mowing height for Bermuda grass, typically 1 to 2 inches. Avoid removing more than one-third of the blade at once, and ensure sharp mower blades. Aeration and dethatching improve air circulation and reduce thatch buildup, which can harbor fungal pathogens. Balanced fertilization is also important; soil testing helps determine specific nutrient needs, and avoiding excessive nitrogen, especially during hot, humid periods, helps prevent lush growth susceptible to disease.
Fungicides
Fungicides can be used for severe or persistent black spots, but proper identification of the specific fungal disease is important before application. These products are often more effective as a preventive measure or when applied in early disease stages. Always follow product label instructions carefully for application rates and safety guidelines. Common types of fungicides for Bermuda grass diseases include systemic and contact varieties.
Pest Management (if Sooty Mold)
If sooty mold is present, control the underlying sap-sucking insect infestation. Addressing these pests eliminates their honeydew secretions, which the mold feeds upon. This may involve using insecticidal soaps or horticultural oils. Once the pest problem is resolved, the sooty mold will disappear as honeydew is no longer produced and is washed away by rain or irrigation.
Preventing Black Spots
Consistent lawn care practices are the most effective way to prevent the recurrence of black spots on Bermuda grass.
Maintain proper watering, mowing, and fertilization.
Regular soil testing ensures balanced nutrients and appropriate pH levels, contributing to overall grass health.
Improve air circulation by pruning surrounding trees or shrubs that create excessive shade, reducing humidity and leaf wetness.
Choose disease-resistant Bermuda grass varieties if establishing a new lawn or overseeding.
Routine inspection allows for early detection, enabling prompt intervention.