Bacterial Blight

Bacterial Blight

Appearance: The disease first becomes evident as small, dark-green, water-soaked lesions on leaves and stipules (paired appendages at the base of a leafstalk in certain plants such as beans). The lesions may enlarge and join together, but are always delimited by the veins and develop a characteristic fan shape. The lesions on the leaflets turn yellowish and later brown and papery.  Lesions may also develop on stems near ground level. Stem lesions may come together, causing the stem to shrivel and die. Heavily infected seed may be discoloured, but light infection has no visible effect on seed.

Disease Cycle: Bacterial blight is caused by the pathogen Pseudomonas syringae pv. pisi. The disease commonly becomes established within a field by sowing infected seed.  During wet weather, bacteria spread from infected to healthy plants by rain splash, wind-borne water droplets, and plant to plant contact. Infection may occur at any stage of plant growth and is most prevalent following frosts.  Plants damaged by frosts or any other physical damage are more susceptible to infection. Rainfall, heavy dews, strong winds, and cold temperatures provide the most favourable conditions for spread of disease within crops.

Disease Control:  Bacterial blight can be avoided by using an integrated approach to management that include planting disease-free seed and crop rotation. The use of clean seed will minimize the possibility of disease, provided the land has not been cropped to peas for several years. If disease occurs, the rotation should be extended to once in four years.

Stubble can be a significant source of inoculum. Destroy by burying, baling or burning infected stubble.  When bacterial blight is detected, steps should be taken to prevent the spread of disease. Where possible harvest infected crops last to avoid contaminating healthy crops and machinery used in an infected crop should be cleaned thoroughly and washed with disinfectant after use.  Fungicides and seed treatments are designed to be active against fungal diseases and are ineffective in the control of bacterial diseases. However, copper based compounds are found to be effective against bacterial blight.