Potatoes were illegal in France between 1748 and 1772.
The farmers considered the vegetable strange and poisonous, even as going as far as claiming the potato caused leprosy and other terrible diseases. The potato was only given to their farm animals and even the poorest, starving peasants were afraid to eat them. The French government was so concerned about the potatoes ill effects that the production and consumption of potatoes was eventually outlawed by the French Parliament in 1748.
Potatoes remained illegal to grow and consume in France for many years until a medical army officer named Antoine Auguste Parmentier was captured by the Prussians during the 7 Year War with England in 1771. Whilst imprisoned Parmentier and his fellow prisoners were fed only potatoes by his captors and, to his surprise, he noted no ill effects as noted by the his government and learned that their perceptions were, in fact, false.