Leaf Rust

Most of the commonly grown dry bean cultivars are susceptible to one or more races of the rust fungus.

Host Crops

Dry beans. Pinto beans are more susceptible to rust than navy or other coloured beans.

Biology

Symptoms first appear as white, slightly raised spots on the lower surfaces of leaves. Small red blisters are then formed on leaves, stems and pods. The lower leaves are the most severely infected. Heavy leaf loss is common. Occasionally, rust will appear on pods but rust on bean stems is rare. The disease is spread by wind, people, and implements.

Symptoms Of Damage

Disease symptoms are typically circular, reddish-dusty spots on the lower leaf surfaces. As the season progresses, the spots may turn from red to black. Rust is most common on mature plants in the fall.

Scouting Techniques

Monitor bean fields early in the season. Look for small, red to reddish-brown pustules on the undersides of the leaves. These rub off when touched.

Control Tips

• Prompt crop destruction after harvest is very important in the control of rust. If this is not done, rust can continue to develop and serve as a major source of inoculum. Brown clouds of rust spores have been observed above abandoned fields, carried by gusts of wind.
• Growers should not plant beans back into the same field the following year because the rust inoculum survives on crop residue. Burning residue and crop rotation will reduce the amount of inoculum. Planting a resistant variety reduces the need for a fungicide program. There are currently no fungicides registered for control of rust on beans in Canada.

For further information, contact your GO representative.