Figures 1 and 2. Bacterial blight of soybean starts with small yellow to brown lesions and grows to larger lesions with a yellowish-green "halo" around the edge. (Photos by Nathan Mueller)

Frequent stormy conditions and rains with cooler weather have resulted in bacterial blight of soybean being pretty common in Nebraska soybean fields.

Bacterial blight of soybean is caused by Pseudomonas syringae  pv. glycinea and is common in Nebraska when conditions are conducive. This disease is typically not a big yield robber, but may cause greater concern if current weather patterns persist.

Bacterial blight on soybean appears as angular lesions. It usually begins in the lower portion of the canopy where small yellow to brown spots appear on the leaves.  The centers of the spots will turn a dark reddish-brown to black and dry out. A yellowish-green "halo" will appear around the edge of water soaked tissue that surrounds the lesions.  Eventually the lesions will fall out of the leaf and the foliage will appear ragged.  In many cases, you can see the growth stages of when a hail or wind storm occurred and observe the lesions associated with those stages.  New growth often will be without lesions. 

The optimum temperature for this disease is around 75°F. As our season heats up, this disease should go away as temperatures move out of the optimum range for growth of the bacterium.  If conditions remain cool, avoid any cultivations or other traffic in fields with this blight as equipment can track the disease through the field and worsen the condition.  Fields with reduced tillage will tend to have increased bacterial blight as the bacterium resides in the residue.

Loren Giesler
Extension Plant Pathologist