Common Bacterial Blight

Causal Agent

Common bacterial blight is caused by the bacteria Xanthomonas axonopodis pv. phaseoli.

Symptoms

On leaves, the initial symptoms are small water-soaked lesions that enlarge over time and turn dry and brown with a yellow halo. The symptoms on pods consist of large water-soaked lesions that get pitted and turn a rusty-red color. Affected seeds often have poor germination, yellow or brown spots on the seed coat, and in severe cases, may be shriveled.

Disease Cycle

The bacteria survive on seed, which can be a major infection source. Another source of inoculum is plant debris left on the soil surface. The bacteria can also survive on non-host plants such as weeds or other crops. Disease is most severe at temperatures between 82 °F to 86 °F (Schwartz et al, 2005). The bacteria can be splashed by rain or irrigation water onto susceptible bean plants as well as being spread by soil, humans, and insects. After infection, it takes 10-14 days for bacteria to build and be spread as secondary inoculum.

Management

It is very important to plant only pathogen-free seed. Good weed control can reduce inoculum from these hosts. A crop rotation of at least 2 years eliminates inoculum from plant debris left on the soil surface. when available. Chemical control must be applied before symptoms appear. Follow the label and use copper-based products on bean foliage.