Maize endophyte or pathogen?

It must be human nature to try to make complex things into simple.  We see this in politics, economics and probably many aspects of human relations seem to want it simple, even if it isn’t.  Those of us that have studied corn and its diseases and certainly anyone growing a corn crop know that the actual environmental interactions with the crop is complex but we still are inclined to try to simplify the interaction between a microbe and the corn plant.
 
In reality, corn roots are invaded by a variety of fungi and bacteria, some of which simply live off of plant products and don’t cause any visible harm to the plants.  Some would call these organisms as endophytes (living with plants but not causing damage). 
 
Presence of these may be detected by the host plant, causing it to produce compounds that restrict the growth of these endophytes into more active plant cells.  In some cases, this appears to restrict more active pathogens.  Species of the genus Trichoderma have been noted as a type of biological control, but also some studies have noted fungal species of Fusarium, Acremonium, Aspergillus, and Botryodiplodia have similar interactions with corn.
 
It becomes more difficult to classify organisms that may once be a harmless endophyte but later, perhaps as the plant begins senescence either because of age, stress or simply shortage of adequate products of photosynthesis in some tissues. Cells in these areas perhaps cannot produce the resistance products needed to stop the foreign organism from killing weakened host tissue.  Do we now designate the organism as a pathogen? 
 
Often it is easier to name a disease, implying that an aggressive pathogen attacked the plant is appealing. Often, however, looking at the more complex aspects that allowed the organism to attack the plant could help avoid the repeat in the future. With many plant physiology, environmental and micro-organisms dynamics it is difficult for research as well as to adequately and completely describe.