Northern stem canker
Over
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.