Dasaro

You could have a blight that greatly reduces wheat growth or drop rate when farmed for a period of time. Or you could have Mad Cow Dieases

whereby cattle only drop rotten flesh, or Avian Flu where the chickens only drop rotten flesh also. It would be easy to adjust loot tables for these type of events...

In fact, nations at war could maybe be able to poison each other's land and animals by spreading such plagues if it were possible to adjust loot tables or growth rates on a regional basis. Or turn off animal spawning in a region as part of a disease scenario. I dunno, I'm just rambling but I like your idea ;P

Well that was what the mongols did to spread the black plague sorta. I am wondering though if we could have this big event where everyone gets infected with a disease and some start to die and so forth...