Cause A fungus, Ustilago striiformis. Many common grasses are hosts, but damage is most severe in bluegrass (Poa),bentgrass (Agrostis), and orchardgrass (Dactylis). It can be a significant problem in pastures, causing a reduction in hay yield and quality. Affected plants are susceptible to root rots and drought stress; they may die during cold winter weather or hot, dry summer conditions..
Plants are infected by spores that are seedborne or when spores that are in soil or thatch germinate in the spring. Primary infection occurs when spores germinate and infect seedlings through the coleoptiles, buds of crowns, or rhizome nodes. The fungus then 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 Plants may be stunted, yellow in color, and slow growing. Infected plants may not head or may produce sterile seed. Sporulation occurs as long, narrow, gray-to-black stripes on leaves and leaf sheaths. Leaf surfaces appear shredded after spore dispersal. Leaf tips curl downward before leaves die. Individual infected plants are especially prone to die during summer months, causing fields to look ragged.
Cultural control
- Plant uninfested seed; use certified seed if available.
- 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 (Group M3) at 8 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
References Alderman, S.C., Ocamb, C.M., and Sedegui, M.S. 2007. Occurrence of Ustilago striiformis in Dactylis glomerata seed production fields in Oregon. Online. Plant Health Progress doi:10.1094/PHP-2007-1023-01-RS
Malvick, D.K. 1991. Stripe smut of forage grasses. University of Illinois Extension Report, RPD No. 314. Online at https://ipm.illinois.edu/diseases/rpds/314.pdf