- Vulnerable Areas
- frost damage
- detect frost damage
- protect vines
- Treatment of already damaged vines
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Phylloxera, hayworm and sourworm or the vine pox mite - vines have many pests. However, these can be effectively combated with pesticides. It's the frost that really worries the winemaker. Although numerous protective measures are already known, farmers are still powerless against climatic conditions. In order to be able to counteract the whims of nature to a certain extent, it is important to recognize frost damage on the vines.
Increased winter protection is essential, especially in so-called frosty conditions. These are areas where the flow of air is impeded. These problematic site conditions are mostly found in valleys and lowlands or in built-up areas where, for example, noise protection dams prove to be disruptive factors. In order to protect the vines from the weather, an increased amount of work is necessary. In some cases, only certain varieties can be grown.
In the case of frost damage to vines, a distinction is made between 3 different groups. The damage is grouped according to the time at which the frost occurred.
- early frost
- winter frost
- late frost
Early frosts set in before the leaves drop in late autumn. However, if the vines are already well developed at this point, there is little risk of consequential damage to the wood. In addition, there are wine varieties that have a high resistance to early frost.
Winter frosts are tolerated differently from grape variety to grape variety. The cold snap disrupts nutrient uptake and storage in reserve cells. If these are already well developed, a temperature drop of up to -20°C has no consequences. The decisive factor for the damage, however, is the course of the weather. A sudden drop in temperature causes more damage than a steady cooling.
Late frosts can still occur until mid-May. Only after the ice saints does the probability decrease. This type of frost is the most feared by winegrowers, as the young vines are particularly susceptible to temperatures below freezing during this time. As little as -1°C or -2°C are hard on the vines at this time of year. While the vines retreat into a kind of hibernation during the cold season between November and March, they sprout again in the coming spring and, like all plants, are very susceptible. This creates a dichotomy between the advantages and disadvantages of a warm spring. On the one hand, early budding means that the wine takes a very long time to mature and therefore has a good chance of increasing the must weight. On the other hand, in April there is an increased risk that the young vines will be damaged by clear, cool nights.
If the wine suffers from frost, the following symptoms appear:
Immediately recognizable symptoms
- reddish brown discoloration of the leaves
- the leaves curl up
- premature leaf shedding
- unripe berries have a reddish-brown discoloration
- her taste changes
- Growths caused by bacterial deposits (mauke)
- Diaphragm or cambium damage
- eye damage
This change in the cane of the grapevine is also known as a wooden bridge. The plants store nutrients in the bast, which, among other things, maintain their stability. From a temperature of approx. -10°C, however, the storage cells freeze, so that the wood becomes ailing and brittle. Only with an increase in thickness does the damage remain absent, since sufficient insulation is guaranteed here. Young vines are particularly at risk because they have usually absorbed only a few nutrients. At first the damage goes unnoticed. It is only after several months that the vintner is hit all the harder when individual parts of the vine or even the entire vine die off. If you cut open diseased canes, you can clearly see a black discoloration of the actually green cambium.
Similar discoloration is seen in eye damage, also known as bud damage. A clear sign of this type of frost on the vine is the delayed budding. In the case of complete frostbite, it even stays away completely.
In the case of apoplexy, budding takes place in spring as usual. However, the wood bursts open on the sticks because the water balance has been thrown out of balance by the frost. If there is an increased need for water in warm summers, the vine collapses and dies. If only small parts are damaged, these symptoms can still occur after several years. Frost damage can then no longer be precisely determined.
notice: Although the symptoms mentioned usually only become visible after a few months, frost damage can be inferred from an early stage. At first the vines are still sprouting and appear to be doing well. They form green leaves and make a healthy impression. On closer inspection, however, no fruit can be seen. For the winemaker, this means the same amount of work as in previous years, although there is no harvest at all.
detect frost damage
In order to determine the extent of the frost damage, the analysis must only be carried out after the Ice Saints. Two methods are common for this:
- a longitudinal section of the eyes
- the removal of one-eyed cuttings, which are checked for renewed sprouting using the swimming method
For the examination, at least ten rods are taken from the vine diagonally from the cultivation. If eye loss exceeds a rate of 30% during the procedures mentioned, acute frost damage is present. A result below this value is considered a natural loss.
To prevent frost damage to vines, the frost conditions described above should be avoided. That means:
- a suitable choice of location when growing the vine (avoid slopes and valleys)
- Cut back greenery regularly
- preferably grow frost-hardy wine varieties
- regular plant protection measures
- do not fertilize, especially not with nitrogenous substances
- only work the soil flat to release as little nitrogen as possible (this promotes early sprouting)
Furthermore, the winter protection should be done individually according to the age of the vine.
New and young plants
- choose a high-altitude training system (especially ground-level vines fall victim to the frost)
- plant and pile up new vines only after the ice saints
- Cut frost rods
- pile up in the fall
- later pruning
- digging in vines
Treatment of already damaged vines
Partially damaged vines
- if the frozen shoots and leaves do not fall off by themselves, they must be removed to protect against botrytis infection
- Cut off subsequent stinging shoots and use as a frost rod if necessary
- Remove shoots from the trunk
- ensure sufficient light supply by removing the disturbing leaves
- frost damage leads to delayed wine ripening. Therefore do two readings
Completely damaged vines
- Do not break shoots on the bogrebe
- Keep grape zone open to prevent rot
- grow new shoots as frost rods
- do not use herbicides to rebuild the vines
- any necessary clearing must be reported to the wine register