Dollar spot is a widespread and economically significant turfgrass disease that affects bermuda lawns, greens, and athletic fields across various climates. Caused by the fungal pathogen Sclerotinia homoeocarpa, this disease targets the leaf blades and sheaths, disrupting the plant's ability to photosynthesize and transport nutrients. While it rarely kills the crown or root system, the visual damage and long-term stress it causes can weaken the bermuda, making it more susceptible to other problems. Understanding the specific conditions that favor dollar spot in bermuda is essential for effective management and maintaining a premium-looking lawn.
Identifying Dollar Spot on Bermuda Grass
The first step in combating this disease is accurate identification, which is particularly important for bermuda due to its aggressive growth habit. The classic symptom is the appearance of small, circular to irregularly shaped tan or bleached-colored spots on the grass blades. These spots typically range from the size of a silver dollar to that of a small fingernail, hence the name. A key diagnostic feature, especially noticeable in the early morning or when dew is present, is a distinct reddish-brown or straw-colored band, often called a "smoke ring," encircling the affected leaf blade just above the soil line. As the disease progresses, the spots may expand and merge, leading to larger patches of dead, flattened turf that give the lawn a faded, scorched appearance.
Environmental Conditions Favoring the Disease
Dollar spot thrives under specific environmental conditions, making certain times of the year particularly challenging for bermuda grass management. The fungus prefers warm days (typically between 60°F and 85°F or 15°C and 29°C) and cool, humid nights. Prolonged leaf wetness, whether from dew, frequent irrigation, or rainfall, is a primary factor that allows the disease to spread. Lawns that are mowed when the grass is wet are at a significantly higher risk. Nutritional stress, particularly a deficiency in nitrogen, also plays a crucial role, as the disease often attacks lawns that are not adequately fed. Poor air circulation and heavy thatch buildup create a microclimate that retains moisture and fosters disease development.
Managing dollar spot in bermuda requires a proactive and integrated approach that combines cultural practices with potential chemical controls. Since the disease flourishes in humid conditions, adjusting your irrigation schedule is paramount. Watering deeply and infrequently in the early morning allows the bermuda foliage to dry quickly during the day, reducing the window of opportunity for the fungus to infect. Ensuring good air circulation by avoiding over-seeding with excessive ground cover and pruning nearby shrubs can help. Regularly mowing with a sharp blade and removing no more than one-third of the leaf blade at a time minimizes stress and prevents the disease from spreading via contaminated equipment. Proper fertility is also critical; a balanced nitrogen application based on a soil test can encourage healthy growth that is more resilient to infection.
Chemical Control Options
In cases where cultural practices are insufficient to control a severe outbreak, fungicide applications may be necessary to protect bermuda grass. Modern fungicide options for homeowners include products containing active ingredients such as azoxystrobin, propiconazole, or thiophanate-methyl. It is crucial to select a fungicide specifically labeled for use on bermuda lawns and to follow the application rates and timing instructions on the label precisely. Resistance to certain fungicides can develop, so rotating between products with different modes of action is a recommended strategy. Always apply fungicides when dew or light rain is expected, as this moisture helps the fungicide to move down the leaf blade and into the site where the fungus is active, maximizing its effectiveness.
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