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Bacterial Blight (Pseudomonas syringae pv. glycinea)Don HershmanUniversity of Kentucky
Bacterial blight is the most common bacterial disease of soybeans and occurs in all areas where soybeans are grown. Although the disease is of limited importance in most production areas, it can cause significant yield reductions on susceptible cultivars when disease pressure is heavy.
The causal bacteria overwinter on soybean seeds and in infested plant residue. Bacterial blight, which is favored by cool rainy weather, is most conspicuous prior to mid-season, but can occur at any time during the season. Dry, hot weather stops disease development. Initial infections commonly occur on seedling with secondary disease outbreaks occuring following windy rainstorms or crop cultivation while the foliage is wet.
Bacterial blight is primarily a leaf disease, although stems, petioles, and pods may be affected. Leaf symptoms begin as small, angular, water-soaked spots that turn yellow and then dark reddish-brown to black with age. Spots are surrounded by a water-soaked margin bordered by a yellow halo. Spots often run together to form irregular brown areas, portions of which may drop out, resulting in a ragged appearance. Management involves planting resistant cultivars and planting pathogen free seed. Cultivation of fields when foliage is wet should be avoided to prevent spreading the pathogen.