It's not a fictional disease. They stopped crop rotations as the soil became too fucked up so everyone is using the same GMO corn but because they are identical they are susceptible to the same disease and it can spread rapidly.

This has happened to lots of crops like bananas and is currently happening again.

The beginning of the movie is people trying to just play their baseball game around a sandstorm getting annoyed at scientists for telling them the world is ending to the point where NASA is in hiding.

Not fictional. Likely reality without the, us getting lucky enough to shoot McConaughey through a wormhole bit.