Halo Blight 

HOSTS

• Legumes

DESCRIPTION

The bacterial infection halo blight is caused by Pseudomonas syringae pv. phaseolica. Other pathovars exist of P. syringae, though each has a distinct range of hosts. Pseudomonas syringae pv. phaseolica is specific to legume crops. 

BIOLOGY

Halo blight overwinters in infected seeds, weeds, and crop residue. The pathogen can be spread mechanically by equipment, people, or water. The bacteria invades host plants through wounds or the stomata. The halos the disease is named for are caused by a toxin the bacteria produces within the plant. These halos are particularly notable in cool weather, and may not be noticeable when the temperature is warmer.

SYMPTOMS

• Small water-soaked lesions on leaves that develop into necrotic spots with distinct yellow halos.
• Foliar chlorosis that is particularly pronounced from 62 °F to 73 °F.
• Pods have water-soaked lesions that may ooze. 

GENERAL MANAGEMENT

• Use certified disease-free seeds. 
• Rotate legumes with nonsusceptible crops for 2-3 years. 
• Avoid overhead irrigation and other watering practices that make plant foliage and soil wet for prolonged periods. 
• Avoid entering fields when plants are wet.