The one potential saving grace is, thanks to the green revolution, we're already growing far more food on the same or less land than was used a century ago, which means that there could be something of a buffer if the use of fertilisers and pesticides has to be curtailed. In an ideal world, the response would be to research pest-resistant crops that have similar yields to what we have now, but I am almost certain that the actual response will be some variation of "get in the pod and starve, peasant!"
I heavily, heavily disagree with you. The green revolution relies on hybrids which were back crossed to gain tonnage over disease/weather resistance, or in some cases the disease evolves fast enough since it isn't single-gene resistance it is an ongoing issues (See: Pecan scab).
For example, older cultivars of high yielding corn was originally based off TMS (Texas, Male Sterile) line which had a cytoplasmic mutation which made it extremely weak to an otherwise rare strain of
Cochliobolus heterostrophus.
Irrigation in the USA is about to get absolutely
fucked when they run out of groundwater. CA and the great plains states especially. Also because apparently climatologists figured out the weather cycle of the west coast is 120 years of decreasing/increasing precipitation (we're right before the apex of the decreasing cycle).
As for the people pushing NO-GMO/organic,
In the words of Norman Borlaug:
Some of the environmental lobbyists of the Western nations are the salt of the earth, but many of them are elitists. They’ve never experienced the physical sensation of hunger. They do their lobbying from comfortable office suites in Washington or Brussels. If they lived just one month amid the misery of the developing world, as I have for fifty years, they’d be crying out for tractors and fertilizer and irrigation canals and be outraged that fashionable elitists back home were trying to deny them these things.
Some no-GMO people do have sound reasoning but paint it as a black and white issue. Who the fuck puts lettuce genes into corn to induce heat tolerance and not test it before releasing it is a fucking retard.
If the price of liberty is eternal vigilance, then the price of mechanized agriculture is as well. Part of the reason why USDA-APHIS is so strict on quarantine is that since we use only a few select cultivars for crops it only takes one virulent pathogen to fuck over the entire crop. Many crop diseases have
no cure, only tolerance or delayed death (Pierces disease, Citrus greening, Coffee Rust come to mind).
Case in point of sleeping on the job, thousand cankers for walnuts is native to Arizona (
Juglans macrocarpa), some dumb ass tried to plant black walnut in Colorado (
J. nigra becomes disjunct in that case as its domain ends around I-35, replaced by
J. microcarpa), and then some other ignorant person brought infected wood back to that native region of
J. nigra and now it is spreading rapidly in Virginia, Ohio, Minnesota, and South Carolina(?).
Edit: Bird/insect tolerance doesn't really exist for fruit/nuts. Maybe for wheat, thank god US native locusts are almost extinct.