To the petrochemical comment: for example look at Paul Stamets. Among the many irons he has in the fire, he knows that certain fungal pathogen species have competitors that are in some cases benign. But fungicides are broad spectrum. They kill off many fungi that would be no problem (and the occasional human liver). The worst weeds and the worst pathogens can often spread faster than their competitors. Only by maintaining a complex ecosystem can you achieve an armistice.
