NPIPM:Flag smut
Authors: Byamukama, E., Smith, M.
Causal Organism
Flag smut is caused by a fungal pathogen Urocystis agropyri .
Symptoms and Signs
Flag smut causes whitish or yellowish to dark grey longitudinal stripes between veins of infected plants. The stripes may appear as blisters between veins. These later may rupture exposing spores of this fungus making the stripes look very black. Infected plants are stunted and have fewer tillers. The leaves on infected plants become distorted/twisted and may be split longitudinally along the blisters.
Disease Impacts
Yield loss data on this disease is scanty but reports from other countries indicate 5-20% grain yield loss. The most important impact of this disease on wheat is restrictions on grain export due to quarantine in some countries.
Life Cycle and Epidemiology
The flag smut fungus infects young wheat plants in the fall but symptoms do not develop until later in spring. The fungus grows within the plant becoming systemic. At heading and flowering growth stages, the fungus produces spores with rapture through the leaf or stem tissues and can be seen as black-gray blisters. The spores produced by the fungus at this stage are called teliospores. These are hardy and can survive in the soil for a long time or on stored seed.
Management Approaches
The flag smut fungus is soilborne and also seedborne. Planting clean certified seed, cleaning equipment from fields that are infected can help reduce the spread of this pathogen. Crop rotation helps break the cycle of the disease but the pathogen can survive in the soil without a suitable host. Therefore, rotations away from small grains should be >5 years. Fungicide seed treatments are effective in managing flag smut. Several systemic seed treatment fungicides are available on market and can be used to treat wheat seed for planting in areas where flag smut is endemic.
Flag smut has not been reported in wheat in our region. However, it is of concern for export markets because it is seed-borne.
Other Online Resources
Kansas Department of Agriculture
Flag Smut Fact Sheet
Plantwise Knowledge Bank
