Depending on weather conditions and disease development in central US cereal crops, stem rust usually arrives in Manitoba and Saskatchewan in mid to late June on southerly winds. The disease generally appears on plants in early summer. Pustules form in 7 to 10 days after infection and break open, releasing masses of brown spores that can infect surrounding plants. Stem rust thrives in temperatures of 20-25ºC (68-77ºF).
Rust spots are very small, circular or elongated, and vivid orange-red in colour. Later in the year, the rust pustules darken because of the production of darkbrown-black spores, which are the overwintering stage of the rust. Infected plants produce fewer tillers, set fewer seeds per head and yield small shrivelled seeds with poor milling quality and food value.
Look for reddish-brown, elongated spore pustules on the stems, leaves, glumes, awns and kernels. The red spore dust may stick to your hands, clothing, and machinery. Later in the season, the pustules produce black overwintering spores.
Choose resistant cultivars where available. Plant early to avoid infection. Apply a foliar fungicide.