Cause A fungus, Ustilago striiformis. Many common turf grasses are hosts, but damage is most severe in bluegrass (Poa) and bentgrass (Agrostis). Plants are infected by spores that are seedborne or in soil or thatch. Primary infection occurs when spores germinate and infect seedlings; then, the fungus spreads within the plant. Dissemination occurs when contaminated seed is planted or when vegetative cuttings from infected mother plants are used to establish new plants. Spores can spread locally on contaminated machinery, such as combines, mowers, and dethatchers. If conditions become unfavorable for growth, the fungus goes dormant. When cool conditions return in spring and fall (about 50°F to 68°F), the fungus resumes growth and invades newly developed tissue.
Symptoms Spores form into long, narrow, gray-to-black stripes in leaves and leaf sheaths. Leaf surfaces appear shredded after spore dispersal, and individual infected plants die, particularly during summer, causing fields to look ragged.
Cultural control
- Plant uninfested seed.
- Use a balanced N-P-K fertilizer at rates needed to maintain good growth. High nitrogen levels may increase the disease.
Chemical control
- Treat seed with a fungicide.
- 42-S Thiram at 8 fl oz/100 lb seed plus a dye. See label for reentry restrictions.