Food is a global commodity and is largely fungible. If every farmer in the US went bankrupt overnight we could easily sustain ourselves by importing food from everywhere else.

Famine is really only a possibility in crushingly impoverished (much of Africa) or criminally mismanaged (Venezuela) economies. The potato blight was a secondary cause of the Irish potato famine, the primary causes were poverty and (English) government incompetence. (or malice, if you prefer) The United States has nothing to worry about.