What to Look For

The large pustules are oval to elongated and are often surrounded by a characteristic torn margin, (Figure 2.24). The pustules are full of reddish- brown spores which fall away easily. They can occur on stems, leaf surfaces, the leaf sheaths and heads. As a plant matures the pustules produce black spores that do not dislodge.

Figure 2.24 Stem rust symptoms on barley

Disease Cycle (See Wheat Rust Life Cycles)

Stem rust survives the summer on volunteer wheat, barley, triticale and grasses including common wheat grass and barley grass. Wet summer weather causes growth of self-sown wheat and other hosts of stem rust. Plants can become heavily infected with stem rust in the autumn and be a source of rust for the new season’s wheat or barley crops. Spores are spread from these hosts to the new crop by the wind. High humidity and heavy dew favour its development. Its spread is most rapid at temperatures near 20°C and is markedly reduced by temperatures below 15°C and above 40°C. If these conditions are followed by a mild winter and a warm wet spring the chances of a stem rust epidemic are high.