New corn diseases

During my short time (uh, 46 years) of looking at corn diseases in the U.S.A. and some time elsewhere, it's interesting, at least to me, that every few years a new corn disease problem is observed.  With each, it takes a few years for the private and public researchers to understand the dynamics that led to the new problem and the solutions. Analysis always comes down to some aspect of the pathogen, host and environment triangle as taught in the beginning of plant pathology courses.
 
Pathogens have their genetics, with variants, survival pressures dependent on feeding on dead and/or alive plant tissue and preference for favorable environment. Environments for corn vary but often are selected by humans for maximum efficiency and productivity of the corn plant in its expected environment.
 
The host corn plant is selected for many characters related to grain productivity, including genetic uniformity such as with single cross hybrids.  Corn genetics usually includes production pathogen defense systems that are reactive to avoid needless wasteful, unneeded anti- pathogen compounds.  Genetics for resistance requires recognition of a pathogen invasion plus genetics to produce the anti-pathogen chemicals.  We are fortunate that corn diversity during its 10,000-year history has allowed existence of genetics for resistance to all potential pathogens somewhere in the corn genome. But within any farmer’s single cross field usually there is only one set of genes and if the hybrid is especially productive it may be common in many fields for a 5-10-year span.
 
Below is my summary of the known interactions with most of the new diseases that have occurred in that last 40+ years in the USA.

It is notable that wide use of corn on corn (COC), minimal tillage and susceptible genetics has led to the increase in each of these diseases to the point of being concerning.  Resistance was identified, reducing the more severe threat, but some environmental aspects are difficult to change because of other beneficial factors. Dynamics of pathogen genetics, environment and corn genetics are in constant change, requiring us to be constantly alert to emergence of new corn diseases.