They are already standard in many fruit growing areas: racks spanned with nets to protect the crops. Hail is one reason for these measures, but there are more.
Like all farmers, checking the weather forecast each day is obligatory for fruit growers as well. "In spring during flowering, frost is our biggest enemy," explains Stefan Haas from Selmnau on Lake Constance, Germany. A few decades ago, these weather conditions led to the introduction of mechanical protective measures. Sprinklers are a proven way of protecting flowers against frost, for example. It might sound paradoxical, but is actually based on a physical phenomenon. When the water freezes, it produces heat of crystallisation, which protects the sensitive flowers from frost damage. "So it is not the ice sheet that protects the flowers, as is sometimes wrongly assumed," corrects fruit grower Stefan Haas. The fruit growers have also had positive experiences with anti-frost candles. They can easily be kept in stock and are readily available for use in an emergency. If there is a threat of night frost in spring, they are simply placed in the rows between the crops and lit. They are extremely flexible in how they are used.
Year-round variety, year-round challenge
Jazz, Kanzi or Gala – in industrialised nations you can find apples in the supermarket all year round. This is due in part to the fact that ripe apples are always hanging from the tree somewhere in the world. On the other hand, cultivation methods are being continuously developed to produce fruit in sufficient quantity and quality. In Germany, there were just under 7,200 orchards in 2016, covering around 31,000 hectares. Baden-Württemberg is the leader in terms of growing areas with 10,000 hectares, followed by Lower Saxony with about 8,200 hectares. Schleswig-Holstein and Saarland are at the bottom end. On the bottom line, however, is that all fruit growers face similar challenges. Retailers and customers demand healthy, high-quality products at an attractive price, regardless of the climatic and meteorological conditions. "This means we have to cultivate our crops accordingly and protect them from the effects of the weather," says Stefan Haas. "Sustainability aspects are also incorporated into production in order to conserve resources." Specifically, so many mutually interdependent factors play a role that the entire industry is faced with complex questions.
Growing fruit in a changing climate
The consequences of climate change are already clearly noticeable in fruit growing. This can be seen in the growing season itself, which has been continuously extended over the past decades. While the apple blossom now begins on average two weeks earlier, the leaf fall of the oak – regarded as the end of the growing season – is largely unchanged. Fifty years ago, the winter – which is determined by the time between leaf fall and hazel flowering – was a good three weeks longer. The cold season has also become milder. This has two consequences for agriculture and for fruit growing: Fewer winter and frost days often means more pathogens. And a longer growing season also means that the plants must be protected longer against fungal attack and similar influences. "At the same time, however, the underlying legal framework is also changing," explains Dr Christian Scheer, Head of Plant Protection at the Kompetenzzentrum Obstbau-Bodensee (Lake Constance Fruit Growing Competence Centre). "In the medium term, this includes the elimination of entire groups of agents, increased residue and distance requirements and reduced spray rates. To continue producing fruit, we need to develop innovative solutions."
Hail and heavy rain in summer and autumn
Hail nets have been in use for over 30 years. "Since the fruit trees were increasingly cultivated and pruned to make them easy to grow and above all to harvest, the crown of the tree, which previously assumed a certain protective function for the fruit, was no longer needed," says Markus Ursch from the main agricultural cooperative in Bolzano, Italy. "Now, due to the modern and lean nurturing systems, many more apples are distributed on the small tree surface and so damage from hail is relatively much worse than in the past." Today, the protection is provided by nets that have been continuously developed over the past few years. "With the high trunks, that would have been technically very difficult." Heavy rainfall is another phenomenon of climate change. However, the danger this poses to fruit is not as great. Pesticides, whether synthetic or biological, are washed off the leaves and therefore no longer effective. In addition, the high humidity increases the risk of fungi or similar pests spreading more quickly. Nets are ineffective in this case. The first fruit growers are therefore beginning to cover their crops with film.
Comparison between nets and film
A project by the Lake Constance Fruit Growing Competence Centre seeks to show the risks and opportunities of these new methods. The aim is to find out how to measurably reduce the use of pesticides while producing healthy and low-residue fruit. The study does this by comparing the various protective measures with each other. "We have created a two-hectare apple orchard that will allow us to compare the different covering systems," says Dr Christian Scheer. "One section is covered with hail protection nets, a second with a rain protection film. BayWa was a valuable partner for the entire project." An insect screen is also being tested. Because increasingly it is not only indigenous pests that threaten the harvest. New species come to us from southern Europe or even from Asia – such as the cherry vinegar fly.
"Without protection, fruit growers are at the mercy of fortune," says Stefan Haas. This point of view is also regularly heard in fruit growers' circles. They must adapt their cultivation methods to the changed conditions, otherwise they will be unable to estimate the harvest yield. "That is why we are in close contact with local fruit growers. With their experience and our research, fruit growing certainly has a future," explains Dr Christian Scheer. The Competence Centre project will certainly play its part here. It is set to run for ten years. "But it will take some time before we can publish the first results," says Dr Christian Scheer. "We are still at the beginning of this experimental set-up."
Climate change is not limited to Europe. It can also be felt on the other side of the globe: in New Zealand, where there are 350 large apple orchards, there are also increasing signs that temperatures are rising permanently. This is reflected in warmer winters and warmer summers. At present, this has no influence on the length of the period from flowering to harvest. However, more and more farmers are using nets to protect their crops from hail, for example. However, this technology is not yet as widespread as in Europe. Cultivation of the country's national fruit has undergone a significant change, because when it gets too warm, the kiwi no longer thrives. This is why some producers are currently switching to the yellow kiwi, which copes better with these conditions. Similar climate changes are also affecting Australia and could affect other fruit-growing regions.
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