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Improving our Understanding of Stem Canker and How to Manage it in Soybean Across the Midwest
Tue - November 15, 2016
Canker on soybean stem
Canker on soybean stem
by Damon Smith, Soybean Plant Pathologist, University of Wisconsin

In recent years stem canker and other diseases caused by the Diaporthe group of fungi, such as pod and stem blight, have become increasingly problematic in the North Central region, with 2014 being an especially prevalent year. Stem canker epidemics can occur in wet springs, and with climate experts predicting a trend of wetter springs, this disease is considered an re-emerging problem in the region.

When multiple species of a fungus can cause several different diseases, it is known as a  “disease complex.”  The Diaporthe complex (also previously known as Phomopsis) is a good example of a disease complex because several species in the Diaporthe/Phomopsis group have been implicated in diseases that include stem canker, Phomopsis seed decay, pod and stem blight, and more recently, Phomopsis root rot.

In an on-going project funded by the North Central Soybean Research Program and the South Dakota Soybean Research and Promotion Council, plant pathologists from South Dakota, Wisconsin, Iowa, and Indiana are working together to unravel the fungal species complex that causes stem canker and related diseases in order to develop more effective and economical management strategies.

To date, sampling in Wisconsin has indicated a mix of Diaporthe longicolla (the causal agent of pod and stem blight) and Diaporthe caulivora (the causal agent of northern stem canker) on soybean stems and seed. In South Dakota, 52 fields across 9 counties were surveyed for soybean stem canker, and Diaporthe species was prevalent in 45 of the fields. Diaporthe longicolla was found to be the primary Diaporthe species in those fields. We are currently identifying samples collected in Indiana, and continue to collect samples in all states during harvest when infested fields are identified. Sampling and identification of Diaporthe species will continue in 2017, as well as disease management trials.

Soybean stem canker is easily misdiagnosed as early crop maturity, sudden death syndrome, Sclerotinia stem rot, or charcoal rot. We developed several outreach publications to help growers identify soybean stem and pod diseases, and to summarize what we currently know about their management.  
Scouting for Soybean Stem Diseases
Scouting for Soybean Stem Diseases - trifold version
Pod and stem blight and Phomopsis seed decay
Stem Canker
Soybean Stem Zone Lines: Fact and Fiction