Stem Canker (Soybeans)

Diaporthe phaseolorum var. caulivora

Soybean stem infected by Stem Canker
Soybean stem infected by Stem Canker. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Stem canker is a soybean disease that attacks and kills lower parts of the main stem. It can cause premature death in soybean fields, decreasing yield by up to 50 percent.
Stem canker is a fungus that overwinters in infested stem debris or the soil, where it can live up to 14 months. It produces spores during periods of heavy rainfall and usually infects younger plants as its spores splash onto the wet foliage. It is a common problem in no-till or continuous soybean fields.
Symptoms of stem canker begin in the leaves, as they start to appear yellowish and the tissue between main veins browns. This generally occurs during the reproductive stage of growth. Initially the foliage may seem to be showing signs of SDS, but upon closer inspection, it can be clearly differentiated by the brown lesions (cankers) on the lower stem. The margins of the canker are dark reddish or purple colored. These cankers first appear as small reddish-brown lesions and eventually develop into large, slightly sunken cankers that partially girdle the stems and/or lower branches. The leaves die but remain attached to the branches. Stem canker can be confused with Phytophthora rot, but is generally higher on the stem.
Stem canker can cause significant yield loss, sometimes reaching 50 percent in favorable conditions. Soybean plants often die prematurely, producing fewer and smaller seeds. The damage is often through large swaths of the affected field and tends to be the greatest when plants are infected during early development. Plants infected during reproductive stages usually have less yield loss.
Areas with no-till farming practices are at a much higher risk of infection than those that till consistently. Tillage of residue into the soil will decrease the survival rate of the fungus and thus reduce further risk of infection. It is best to avoid planting extremely early, especially in wet fields.
Fields that have high fertility or high soil organic matter are at risk for stem canker infection. Maintain a well-balanced soil mixture to reduce risk of impact. 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.
There are resistant varieties of soybeans available that are highly recommended if there is an at-risk field. It is also known to be helpful for crop rotation practices to be used. After a severe infestation, it's best to rotate into a non-host crop for at least two years