Danger for apple trees: Mistletoe plagues fruit growers

The many green leaves on the apple trees shouldn’t be like this, not just before the end of the year. They also do not belong directly to the apple tree. Mistletoe spreads out here on Stefan Bosch’s orchards in Sternenfels – located between Karlsruhe and Heilbronn. He speaks of a catastrophe. Bosch has around 50 fruit trees. The apple in particular was affected. A bit of cherry too. “Pears have long been considered mistletoe-resistant,” he says. “That’s not the case anymore.” Only the walnut doesn’t have anything yet.

Mistletoe is a symbol of peace, love and – because it is evergreen – eternal life. Asterix fans know them because the druid Miraculix needs them for his magic potion. And especially in Christmas carols is kissed romantically under the mistletoe.

damage to apple trees

However, for nature conservationists and fruit growers, mistletoe is a semi-parasite: although they carry out photosynthesis themselves, they grow on other trees with the help of suction roots and deprive their hosts of water and nutrients. According to the nature conservation organization Nabu, this can cause growths and cancerous damage in apple trees. Sometimes branches break under the load. If the mistletoe is not removed, entire stands of trees are at risk.

In regions of southern and central Germany, mistletoe has become a real plague. But mistletoe has also reached northern Germany. It has been spreading rapidly since the 1990s. He had a mistletoe bush 20 years ago, reports Stefan Bosch, who is also a specialist for ornithology and bird protection in the Nabu state association in Baden-W├╝rttemberg. “I showed it as a special feature.” In the meantime, some trees have fallen to their knees under the mistletoe. Around 400 trees only in the Diefenbach district were affected.

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Climate change as a reason for spread

The Nabu explains the strong spread primarily with climate change: it favors bird species that distribute mistletoe. Summer heat and drought stress also weakened the host trees. Orchards run by hobbyists are also often not cared for enough to really get the mistletoe under control.

“You would have to do a big campaign now and then keep adding to it,” says Bosch. Contrary to what is often assumed, mistletoe is not under nature protection and can be cut off and used as an Advent decoration, for example. In the best-case scenario, the mistletoe could be pushed back a bit, he says.

Birds spread the plant

But that is work: Bosch calculates a good one to two hours per tree. “You have to climb in and make sure you get every little one,” he explains. “Otherwise they will come next year.”

Mistletoe forms sticky, white cloudberries to help it spread. They can stick to the beaks of birds and are wiped off the host plant when they are cleaned – or get on the bark of a host tree via bird droppings. Thrushes and corvids, hawfinches, starlings, waxwings, tits, thistles and chaffinches, robins, yellowhammers and nuthatches feed on the berries. However, these can also come loose and “drop” onto branches below them.

Old plant, old customs

According to Nabu, it takes about a year to dock onto the host plants’ pathways. Mistletoe can then grow up to 70 years old. Garden experts at the University of Hohenheim report that if they are torn off in a storm, they will not die. They grow back from their stump. Each year they branch once as they grow, so you can tell their age by the number of forks. In this way, spherical bushes up to a meter tall can form.

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The experts also provide information about mistletoe customs: in order to prevent mischief, mistletoe should always be hung up so that it does not touch the ground – especially over doors. “Because where people go in and out, good luck or bad luck can also come in.” At the beginning of the 18th century, the custom of kissing girls under mistletoe originated in England and France. After each kissing meeting, a berry should be picked. “The kissing is only over when the branch is completely picked off.”

Hildegard von Bingen – Mistletoe is medicine

Mistletoe is also said to have healing powers. The nun and natural polymath Hildegard von Bingen was convinced of this and recommended the plant for liver diseases, the Hohenheimers know to report. “Today, mistletoe preparations are used to lower blood pressure or in the accompanying treatment of cancer.” Some species of insects, such as highly endangered bugs, are dependent on deciduous mistletoe, warns Nabu. Therefore, if possible, entomologists should be consulted before control measures are taken.

Research into the causes of the spread, possible connections with certain types of fruit or heavy metals in the soil is still in its infancy. But what scientists already know: According to Nabu, some trees are developing strategies against mistletoe. In the case of pear trees, for example, the tissue around the germination site dies first – and finally the semi-parasite itself.

RND/dpa

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