Anyone who last passed the orchards of the Bavarian Fruit Center in Hallbergmoos in the morning was presented with an unusual spectacle: the apple and pear trees were covered with a thick ice coating overnight. What happened here?
Hallbergmoos - "In order to protect the flowers of the fruit trees, which are unusually well developed at this time of year, from freezing to frost, they are irrigated with water during the night," reports Dr. Michael Neumüller, head of the Bavarian Fruit Center. “The water freezes on the branches and flower buds. Heat is released during the freezing process. This warmth is transferred to the flowers by the ice sheet and prevents them from being damaged in the frosty nights. ”
The irrigation may only be switched off in the morning, when the temperature is well above freezing and the sun warms the ice. Without the frost protection sprinkling, as it is called in technical jargon, this year's apple and pear harvest would probably have been wholly or at least partially: The onset of cold, combined with the night frosts, is currently causing problems for many plants.
The water pump or the tractor that drives it must never fail
For background: You know that: If you want to melt an ice cube, you have to hold it in your warm hands for a long time or leave it at room temperature for much longer. So you have to supply thermal energy. Conversely, it is such that exactly this energy is released when water is frozen into ice. The fruit farmers take advantage of this: They sprinkle the areas with fruit trees that they want to protect against frost, with water on the frosty night. This freezes on the shoots and leaves, and this process releases thermal energy. This prevents the temperature on the flowers from falling too low.
However, water has to be replenished throughout the night; because when the water stops freezing, the ice quickly takes on the temperature of the surroundings, which leads to even greater damage than would have occurred without irrigation. The water pump or the tractor that drives it must not fail under any circumstances.
The fact that there is frost at night in late March / early April is not uncommon and usually does not bother the flowers of the fruit trees during this time. However, it is problematic that the shoots started four weeks earlier than usual due to the mild winter. "That is why the young flowers have developed to such an extent that they are damaged at temperatures below -2 ˚C," says Neumüller. In the night from Monday to Tuesday -8 ˚C was measured in the orchards. The lowest temperature measured between November and February was - 6˚C. "Without suitable protective measures, it is no longer possible to produce fruit regularly," says Neumüller. ft