The three common bacterial leaf diseases of beans.

Bill Kerr gives advice on how to recognise and treat halo blight, common blight and bacterial brown spot in a bean crop.

- Bill Kerr

Halo blight is a very destructive disease that can spread rapidly under certain conditions. As the name suggestions, the lesions on the bean leaves and pods are surrounded by a light-yellow area resembling a halo.

The water-soaked spots in the centre of the halo become reddish brown and ooze bacteria that can be spread via driving rain, sprinkler irrigation, implements, people, hares, birds, or insects. This means the bacteria can be transported to your land from a neighbour’s infected crop.

This disease requires cool, moist conditions and is consequently a greater hazard for those growing beans in high-rainfall areas.

There are a number of different halo blight races. The resistant genes should protect your beans against the race in your area. With marker-assisted breeding, one can include various genes in one variety for the greatest protection. One can even have a gene that allows the leaves to become infected but prevents the pods from following suit.