The organisation estimated that nearly 1.5 million tonnes could be lost on French soil, a drop of “at least 20 percent compared to the average of the last twenty years”.
Geoffroy d’Evry, a farmer in the Oise region and president of the UNPT, noted that usually “when there is a heatwave, the potato stops its cycle, then starts growing again” when temperatures drop.
However, the persistent drought and the succession of heatwaves in the summer have blocked the development of the tubers for a long time.
Mr d’Evry added: “In the memory of any potato grower in the north of France, we have never experienced a situation like this.”
The average French person eats 52 kilos of potatoes a year, and 64 percent of the population eats it every week. Yves Marin, a retail consultant with Bartle consultancy said of the crop: “It is the third most consumed starch on the planet after rice and wheat.
“We were preparing to spend the winter without heating or electricity, and now we discover that there may not even be potatoes for dinner?”
Mr Marin noted however that France is the leading European exporter of potatoes, with more than 2 million potatoes going abroad each year and added that “all we have to do is sell less abroad”.
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The Légumes de France federation has also estimated losses of between 25 percent and 35 percent in the production and yield of vegetables.
Laurent Grandin, president of the fruit and vegetable trade association Interfel, told the website actu.fr: “With the rise in temperatures, the drought, and therefore the water restrictions, the plants have developed water stress, which has reduced production.
“As they lack watering, they favour their survival and produce less, and of lower quality.”
Jacques Rouchaussé, president of Légumes de France, added some sowings have also been postponed to prevent the seeds from burning due to the heat. He said: “We are therefore likely to have delays in the production of turnips, carrots and radishes.”
Françoise Roch, president of the National Federation of Fruit Producers noted “apples are going to be a little smaller” after the heatwave, “but production has been good overall”.
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Mr Rouchaussé then warned that even if the risk of a vegetable shortage is ruled out, “there will definitely be fewer goods” which could spike prices.
According to INSEE, the price of fresh vegetables has already risen by 4.9 percent over one year.
However, this figure is lower than the inflation of all food products over the same period, which has risen by 6.8 percent.
It comes after France suffered multiple heatwaves, wildfires and drought conditions since June.
On June 16, the town of St-Jean-de-Minervois in southern France reached 40C (104F), the earliest that the country (excluding Corsica) has ever reached above 40C.
It also comes after French President Emmanuel Macron called on citizens to cut down on their energy usage.
He said: “Everyone has a role to play. The best energy is the one we do not consume.”
He urged people to “save 10 percent of what we currently consume” and said it was necessary for people to turn down the air conditioning when it is hot and, this winter, to “settle on a heating reference of around 19C”.
Deputy of Haut Rhin Raphael Schellenberger mocked Mr Macron, saying: “From now on, the President of the Republic takes care of everything: even the temperature inside your home.”
National Rally MP for Gard Nicolas Meizonet added: “So the French have to pay for the inconsistencies of its leaders?
“We were waiting for excuses, instead we got threats!”