Bacterial Pustule (Soybean)

Xanthomonas axonopodis pv. glycines

Soybean leaf infected by Bacterial Postule
Soybean leaf infected by Bacterial Postule. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Bacterial pustule is a common disease in moist, warm areas. It is not known to be a significant factor in yield loss due to resistant varieties that are currently in place. It is characterized by small lesions on the leaves that result in giving leaves a tattered look. Severe cases cause plant defoliation.
Bacterial pustule tends to survive well in infected crop residue on the soil surface or in seeds. It prefers wet or rainy weather and usually shows up around a week after large storms. Optimal temperature for bacterial pustule development is 86 to 91 degrees F. The bacteria are transferred to the live plants through splashing water or windblown rain. Infection can happen at any time throughout the season.
Symptoms begin as small, light green lesions on the surface of the leaves. These lesions are more prominent on the undersides of the leaves and have a slightly raised reddish-brown center. As the lesions mature, they darken in color, grow in size, and cause large areas of the leaf surrounding them to die. As the dead areas begin to die, they are ripped away by the wind and rain, leaving the foliage with a tattered appearance. Symptoms of bacterial postule resemble those of bacterial leaf blight, often occuring together on the same plant.
Bacterial Pustule on Soybean Leaf
A closer look at bacterial pustule infection on a soybean leaf. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Damage overall is generally minimal due to resistant varieties currently in use. Foliage reduction in severe infections can cause some yield loss.
Tilling crop residue under is important for promoting decomposition of diseased tissue. It's also important to use disease-free seed. Sometimes bacteria can be spread through the use of wet machinery from an infected field, so avoid using machinery during wet conditions.
Please contact your local plant pathologist to learn what is most effective in your area and how to use it best. Always read and follow all label instructions.
Planting disease-free and resistant varieties to avoid infection is a common method used by producers. Rotating in nonhost crops can also be a very effective method of controlling the growth of bacterial postule.