July 11, 2008

Frequent rains and stormy conditions have resulted in bacterial blight being prevalent this year in soybean fields. Bacterial blight caused by Pseudomonas syringae pv. glycinea is present across Nebraska.

Soybean leaf with injury and blight.

Bacterial blight on soybean will appear as angular lesions, which begin as small yellow to brown spots 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.

Bacterial blight is favored by stormy conditions which provide wounds on the leaves for entry and wet conditions with milder temperatures. The optimum temperature for development is around 75°F and infections usually start in the lower portion of the canopy or the region of the canopy that received the damage if stormy conditions occurred. New growth will often appear healthy.

As temperatures heat up, the disease should go away and it is usually not a yield limiting problem in Nebraska. One management option would be to not traffic fields with blight when they are wet and the bacterium can be spread this way. If you are making those final herbicide applications, spray fields with blight later in the day.

For more information on bacterial blight of soybean visit the Plant Disease Central Web site at: http://pdc.unl.edu/agriculturecrops/soybeans/bacterialblight.

Loren J. Giesler
Extension Plant Pathologist