Bacterial Blight On The Increase In Some Soybean Fields

 

Bacterial blight was found in several soybean fields scouted in Brookings, Deuel and Moody counties. Recent heavy storms and/or hail injury may have increase the prevalence of bacterial blight. As the weather heats back up, typically over the optimum 75 degrees, the growth of this bacterium will be stalled.

 

 

Symptoms of bacterial blight are often confused with soybean brown spot, which is a fungal disease.

 

 

Bacterial blight is caused by Pseudomonas syringae pv. glycinea. Bacterial blight can occur on all above ground plant parts, but is most evident on leaves in the mid to upper canopy. Bacterial blight lesions start as small angular spots surrounded by a yellow halo. The lesions expand and coalesce to form large brown patches. The brown patch centers may fall out leading to leaf tearing/tattering (Figure 1).

 

 

 

In contrast, soybean brown spot lesions are also dark brown but the yellow halo around the lesion is not obvious except in advanced heavy spots (Figure 2). Brown spot, also known as Septoria leaf spot is a fungal disease caused by Septoria glycines. Usually brown spot remains in lower leaves and does not cause significant yield loss. However, under heavy infection, brown spot can result in premature leaf fall leading to significant yield loss.