Plant Disease: Bacterial Pustule

Taxonomy:

Distribution:

• This disease has been reported in most parts of the world where soybeans are grown and the climate is warm with frequent rain.


• Damage can occur by causing premature defoliation and a reduction in seed size and quantity.


• This disease is most prevalent later in the growing season.

Symptoms:

Water soaking is an early sign

• Symptoms of bacterial pustule are very similar to those of bacterial blight and are more noticeable in newer than older leaves.


• Initial infestation results in the development of tiny pale green spots on the new leaves.


• These spots have raised centers that may develop on either surface of the leaf but are more common on the lower leaf surface.


• As the disease progresses, small light colored pustules will form in the center of the spots.


• Spots may merge together to form irregular areas that appear as lesions.


• This disease can easily be confused with soybean rust.


• Mature soybean rust pustules have a small opening at the top for spore release. Bacterial pustule lesions lack the opening on top and spores.


• If an opening is present, it is typically a linear crack across the surface of the pustule.


• These features can only be seen under magnification (20 X recommended).


• Bacterial pustule symptoms are also similar to those of bacterial blight but lesions do not appear water soaked and will have raised centers.

Notice Pustules along Viens

Epidemiology:

• Like bacterial blight, bacterial pustule over winters in crop residue and is carried by the wind or water droplets from the ground to the plant.


• In addition, the disease can be spread during cultivation while the foliage is wet.


• The bacterium will enter the plant through natural openings and wounds.


• Warm weather with frequent showers promotes the development of this disease.


• Unlike bacterial blight, warm temperatures do not limit development of bacterial pustule, as the optimal temperatures for disease development ranges from 86 - 92 ° F.

Management:

• While this disease is not typically yield limiting in Nebraska, producers should consider the following options in problems fields.


• The best management tool is to prevent disease establishment. Cultivars that are not highly susceptible to the disease should be considered for planting.


• Crop rotation can be an effective method to avoid inoculum from a previously infected crop.


• Incorporating crop residue by tillage will reduce the amount of inoculum available in the spring to infect plants but there are moisture and erosion issues to be considered.


• To prevent the spread of disease, limit cultivation to times when the foliage is dry.


• Copper fungicides are labeled for control of bacterial blight on soybeans but need to be applied early in the disease cycle to be effective.