We had one variety of plant go bad, and they were diagnosed with a root fungus. The fungicide we were directed to use was really nasty stuff, but it only worked partially. We also use fungicides in our mum field every fall.
I swear, with the array and amount of pesticides, fungicides, herbicides and fertilizers we have in our utility building, we could probably do a LOT of damage if we wanted to. Probably doing more environmental damage than we really want to. :( We try to minimize the impact by feeding the chemicals through the drip irrigation system, but that doesn't work for the field garden.