I didn't specify a timeline, so I don't understand why both you and Colman thought of "quickly". I am thinking of decades for the whole process.

only a tiny fraction of all transport is foodstuff. And this would get priority

Why do you think so? I am not at all certain. It could get priority after government gets priority, which only means that pressures will be stronger elsewhere. (A hefty recession after the creduction of production capacity in major industries, but this time permanent unlike in the thirties, wouldn't be pretty.)

Pesticides are a tiny volume of petrochemistry... Diesel for industrial machinery is again a tiny amount of total consumption.

It's not the amount that matters most. You forget about costs rising strongly for farmers. Couple that with the lending market one could expect.

_{*Lunatic*, n.
One whose delusions are out of fashion.}