Malthusians and Neo-Malthusians believe that, eventually, the population of the earth will be exceeding the number of people able to be sustained by the earth's food production. As such, they advocated different forms of population control.

However, it appears that an increase in the population beyond that of the food supply would cause an increase in the overall real price for food.

Proponents of Malthusianism, evidently, are not waiting for food prices to rise before advocating population control, but I do not see how we should be worried until the real price of food increases.

If Malthusianism is correct, how soon before the population crash would prices begin to rise?