Diplodia ear rot

​Starting to hear reports of Diplodia ear rot as corn harvest begins.  This disease is caused by a fungus that was once named Diplodia maydis or Diplodia zeae but now is considered a single species Stenocarpella maydis.  It is believed to only infect corn, overwintering in diseased corn stalks or ears.  Infection of the ear occurs through silks or the husks.  Once inside the ear, the fungus feeds on the developing kernels, cob and adjacent husk.  The result is moldy grain that dries slowly while in the tight husk.
 
Infection usually occurs shortly after silking and especially if it is rainy during that period.  The rain not only stimulates the production of fungal spores but also delays pollination, resulting in longer exposure to fungal infection as the un-pollinated silks are vulnerable spores germinating and growing down the silk channel to the ovules. Infection may be more obvious at the base of the ear, perhaps indicating rain at the beginning of the silking or at the tip of the ear, suggesting rain a few days later.  This interaction with rain timing and relative dates of silking makes resistance conclusions very tenable as susceptibility can be confused with bad timing for that season. Also, it is probable that late-season ear uprightness is not a factor influencing susceptibility to this disease.
 
Diplodia ear rot is associated with continuous corn culture, allowing the fungus to build in intensity over years. Grain quality reduction is obvious in heavily infected fields.