Northern stem canker
the last couple of weeks dead soybean plants with petioles and leaves
still attached have been noted in some fields. Northern stem canker
caused by the fungus Diaporthe phaseolorum var. caulivora has been identified as a potential causal agent.
At this stage of plant maturity, it can be difficult to easily identify the cause of disease. Phytophthora stem rot can easily be confused with Northern stem canker. One of the key differences is the location of lesions. Phytophthora will produce a brown to black lesion on the stem that initiates from below the soil line, while northern stem canker will produce lesions that initiate around nodes, appear sunken and may girdle the stem. Check the roots, plants with Phytophthora rot will have rotten and reduced root mass, while those infected with northern stem canker will appear healthy.
Northern stem canker produced severe yield losses back in the 1950’s across the North Central region, it was controlled by the introduction of resistant varieties, but there are reports that it is on the rise. For disease management, use resistant or moderately resistant cultivars, seed treatments as the pathogen is seed transmissible, and tillage may also be beneficial.