Bacterial Diseases in Beans

Halo blight has been identified in the kidney beans trials at Ridgetown Campus. In snap beans it can be difficult to distinguish between halo blight and common blight in the field.

Halo blight is most active when temperatures are in the 10-20°C (61-68°F) range. Infected plants also develop water-soaked and necrotic lesions surrounded by a yellow halo. Under cooler temperature conditions, halo blight may cause the entire plant to become yellow or chlorotic. Warm temperatures are less favourable for the spread of this disease.

Common blight prefers warm, humid conditions and temperatures of 25-30°C (77-86°F). Water soaked lesions appear on the under side of the leaf. As the lesion develops it becomes brown and necrotic, often surrounded by a yellow border. Under favourable weather conditions, the lesions will grow together, giving the crop a burned appearance.

Both bacterial diseases will infect the pods. Small (2-3 mm) water soaked lesions eventually turn dark reddish brown. In yellow beans the pod lesions may remain green. The pods may become twisted and curled where lesions are present.

Infected seed is thought to be the primary source of infection. However, both diseases overwinter in crop residue. Secondary infections are often caused by rain and splashing soil. Copper fungicides help to stem the spread of these bacterial infections if they are applied before the symptoms become wide-spread.

If bacterial diseases are felt to be a threat, begin copper applications early in the crop’s development to destroy any seed or soil borne (primary) innoculum. This strategy will help to prevent ongoing secondary infections. Keep in mind that copper fungicides do not have a long residual control and may have to be re-applied regularly (every 7-10 days.)

Halo Blight Infected Leaf

Pod Lesions