Stripe smut is a fungal disease that can affect the appearance and health of various turfgrasses, particularly cool-season varieties like Kentucky bluegrass, bentgrasses, and fescues. This ailment weakens the grass, leading to stunted growth and discolored foliage. The disease can spread throughout a lawn, diminishing its overall vigor and aesthetic quality.
Recognizing Stripe Smut
Identifying stripe smut often begins with observing yellow or brown stunted areas within a lawn. Upon closer inspection, infected grass blades reveal characteristic symptoms. Early stages show yellow-green streaks, which later turn gray.
These streaks rupture, exposing masses of black, powdery spores, giving the disease its “smutty” appearance. After rupturing, the diseased leaves shred into ribbons and curl downwards, eventually turning dark brown and dying. Symptoms are most noticeable in cooler, damp weather, particularly during spring and fall (50°F to 60°F / 10°C to 16°C).
The Pathogen and Its Cycle
Stripe smut is caused by the fungus Ustilago striiformis. The fungus persists as spores in the soil or as mycelium within infected grass crowns and rhizomes. Dormant spores germinate in favorable conditions, infecting new grass plants.
Infection occurs in young seedlings or new tillers, often when spores contaminate seeds or are in the soil. Once inside the plant, the fungus grows systematically, developing throughout the plant’s vascular system. Spores spread by wind, water, and mowing equipment, facilitating propagation across turf areas.
Strategies for Control
Managing stripe smut involves a combination of cultural practices and, when necessary, chemical interventions to reduce disease severity and spread. Proper irrigation is important, ensuring adequate moisture based on evapotranspiration needs while avoiding prolonged periods of leaf wetness that favor fungal growth. Over-fertilization with nitrogen, especially during summer months, can exacerbate symptoms, so maintaining balanced nutrient levels is beneficial.
Selecting resistant turfgrass varieties is a highly effective long-term control measure; for instance, some Kentucky bluegrass cultivars exhibit good resistance to stripe smut. Blends of multiple resistant cultivars are often recommended to enhance overall turf resilience. Cultural practices like core aeration can improve soil drainage and reduce dampness, creating less favorable conditions for the pathogen.
Sanitation of mowing equipment helps prevent the spread of spores from infected to healthy areas. If the disease is severe, fungicides can be applied. Systemic fungicides, such as those in the DMI group (e.g., fenarimol, triadimefon, propiconazole), are particularly effective as they are absorbed by the plant. Applying fungicides in late fall, before the disease becomes dormant, or using fungicide-treated seeds for new plantings, can help prevent initial infections.