Bacterial blight of soybean
Bacterial blight is caused by Pseudomonas savastanoi pv. glycinea, and is usually one of the first foliar diseases to occur on soybean. Bacterial blight seldom causes serious yield loss. Symptoms usually begin in the upper canopy because young leaves are most susceptible. Small, angular, reddish-brown lesions are surrounded by a yellow halo. As the disease progresses, lesions often grow together to produce large, irregularly shaped dead areas. Centers of older lesions frequently fall out, causing leaves to appear tattered.
The bacteria survive winters in crop residue and seed and are spread by rain and wind. Bacteria can survive on leaf surfaces during the season and infect plants when conditions are suitable. Infection occurs through stomates (natural leaf openings allowing air exchange) and wounds caused by wind, hail, etc. Thus, outbreaks are common after rainstorms with high winds. Cool temperatures favor bacterial blight; warmer temperatures will slow or stop disease development.
Crop rotation and tillage reduce survival of the bacteria. Non-hosts include alfalfa, corn, and small grains; other legume crops can be alternative hosts.
Gallery Images: D. Mueller and A. Sisson