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Soybean Stem Canker
is caused by a soilborne fungus called Diaporthe phaseolorum. The prevalence of
stem canker depends on the amount of rainfall received during the early stages
of soybean growth. The fungus produces many tiny spores on soybean debris, and
the spores are carried by splashing rain to healthy soybeans. Infected plants
will not have symptoms until midsummer, often late July. Observations indicate
that hail injury may enhance the development of this disease. Plants with stem
canker are often first noticed in field areas where the crop stand is thin. An
infected plant will have one brown, slightly sunken lesion at the base of a
branch or a leaf petiole on one side of the stem. The lesion expands along the
stem and sometimes severely girdles it. Branches on the upper part of the plant
can be killed, and the dead plants are most visible after the R3 stage.
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