Fusarium on corn

​The fungal genus Fusarium is a ubiquitous inhabitant of corn and other grasses.  Several species of Fusarium are also associated with their sexual stage of the genus Gibberella. Fusarium is recognized microscopically by the shape of their asexually produced spores (conidia) that are produced in abundance and dispersed by wind currents.  Distinction between Fusarium species requires specific lab methods but quick microscopic exam for the curved, multicellular, hyaline conidia leads to a quick analysis as Fusarium.
 
Fusarium species do not tend to be aggressive pathogens of vigorous, living corn tissue but almost more of an inhabitant, not actively killing cell tissue but more of a scavenger of dying or dead tissue.  Some Fusarium species such as F. verticillioides (formerly named F. moniliforme not only produce multicell conidia but are known to produce single cell microconidia that apparently can move in the vascular system of a corn plant.  Ease of movement within and outside of the corn plant and the ability to infect weakened and dead corn tissue allows for this fungus to be found in nearly all dead corn tissue.  This can include leaf tissue injured by insects, hail or other physically injury.  Active leaf pathogens such as Exserohilum turcicum (cause of northern leaf blight, apparently ward off Fusarium invasion via antibiotics.  
 
Nearly every dead stalk will have a Fusarium species among its inhabitants.  If the dead tissue includes the more easily identified symptoms of Gibberella zeae (the sexual stage of Fusarium graminearum) the diagnosis will be Gibberella stalk rot.  If black streaks typical of the anthracnose that will be the announced cause.  Diplodia maydis, now called Stenocarpella maydis, is distinguished by its symptoms as well.  If none of these symptoms are evident, the ever-present Fusarium, is diagnosed as the cause of Fusarium stalk rot. 
 
The actual cause of death of the stalk tissue is the complex interactions of photosynthesis and distribution of carbohydrates during grain fill of the corn plant. The fungi present are able to digest the dying and dead tissue.  If none of the easily identified fungi associated with stalk rot are found, there is always Fusarium stalk rot.  The ease of identifying a fungus in the tissue, implying the case of the early death of the plant, can lead to avoiding the diagnosis of why the plant died before completion of grain fil.