Crop & Pest Report


| Share

Bacterial Blight Appearing on Soybeans (07/23/20)

Recent thunderstorms provided a perfect environment for bacterial blight on soybeans, and the disease is showing up widely across the state.

Recent thunderstorms provided a perfect environment for bacterial blight on soybeans, and the disease is showing up widely across the state.  Bacterial blight on soybeans is very unlikely to be economically important, and even if it were, fungicides are not effective. Thus, the disease needs no management, but it is important to know the disease is not something severe.  Notably, bacterial blight on other crops, such as dry beans, is economically important (and that is occurring too).

Like other bacterial diseases, leaf wounding is needed for infection.  Commonly this means thunderstorms, high winds, heavy rain, or hail. The disease is usually observed on the upper leaves as small necrotic and angular spots with bright yellow halos. Lesions often coalesce and may tear or fall out.

I encourage growers to use the Soybean Disease Diagnostic Card set to help identify diseases occurring in the fields. The Card Series has information on 23 diseases, with images on the front of the card and a description of key symptoms and other important information on the back.  My colleague at the University of MN (Dean Malvick) and I created these specifically for our region and selected a high quality synthetic material that is resistant to water, creasing, tearing and light reflection.  The set consists of 24, 3½” x 8” cards bound by a single ring; and it’s field worthy!  (first photo)


Using bacteria blight as an example, I am holding leaves next to the cards to compare symptoms (Second Photo). The backside of the card tells us that we need thunderstorms to get the infection started, and that its rarely economically important, and what the disease might be confused with.


The pdf version is free for download at, or and physical copies may be available through NDSU Extension.  We thank the North Dakota Soybean Council and the Minnesota Research and Promotion Council for supporting the development and funding this publication.


Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

USDA logo

Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.