Mistletoe – a green parasite of trees

Mistletoe – a green tree parasite threatening Polish forests

Biology and harmful effects of mistletoe

The scale of the mistletoe problem in Poland

Prevention and control of mistletoe

What can we do?

From our perspective, it’s a semi-parasite

Mistletoe - a green tree parasite threatening Polish forests

Mistletoe (Viscum album L.) is a perennial parasitic shrub from the mistletoe family (Viscaceae). It commonly occurs in European forests, including Poland. Although visually attractive, with characteristic green shoots and white fruits, it poses a serious threat to Polish tree stands. In this article, we will discuss the problem of mistletoe in Polish forests, present methods of preventing and combating this parasite, and consider what we can do to limit its expansion. Mistletoe – a green parasite of trees, literally sucks the life out of a tree stand.

Biology and harmful effects of mistletoe

Mistletoe parasitizes various species of deciduous trees, preferring pines, poplars, oaks and lindens. It attaches to branches using haustoria, specialized roots that penetrate the wood of the host tree and draw water and nutrients from it. This parasite weakens trees, reducing their photosynthesis and inhibiting growth. In extreme cases, it can lead to the death of branches and even entire trees. In addition to directly weakening trees, mistletoe can also indirectly affect their health by increasing their susceptibility to diseases and pests. Moreover, mistletoe fruits are attractive to birds, which when eating them spread the parasite’s seeds to other trees, contributing to its spread.

Scale of the mistletoe problem in Poland

Mistletoe is commonly found in Polish forests and its occurrence is constantly expanding. According to the estimates of the State Forests, this parasite infects approximately 10% of tree stands in the country. Pine forests are particularly at risk, where mistletoe may constitute up to 30% of all trees.

• The spread of mistletoe is caused by a number of factors. We provide them in the subsections below.

• Climate Change: Warmer and drier winters favor the growth and spread of mistletoe.

• Air Pollution: Nitrogen dioxide and other air pollutants weaken trees, making them more susceptible to parasites.

• Intensive forest use: Logging and other forestry operations can fragment forest stands and facilitate the spread of mistletoe.

Mistletoe prevention and control

There are a number of methods for preventing and combating mistletoe that can be used in Polish forests. The most important of them include:

• monitoring of tree stands, regular observations of tree stands allow for early detection of mistletoe and taking appropriate actions;

• removing mistletoe from trees: mistletoe can be removed from trees manually or using specialized devices. This must be done carefully so as not to damage the host trees;

• use of chemicals. There are also chemical methods of combating mistletoe, but their use should be limited to exceptional cases due to the negative impact on the environment;

• planting mistletoe-resistant trees. Some tree species, such as larch and birch, are less susceptible to mistletoe. Planting these species can help reduce the spread of the parasite.

What can we do?

In addition to the actions taken by the State Forests, each of us can also contribute to limiting the expansion of mistletoe. We can do this by:

• reporting the occurrence of mistletoe – if we notice mistletoe on trees while walking in the forest, we can report it to the forest district within which the forest is located;

• using ecological plant protection methods – we can avoid the use of chemical plant protection products in our gardens and plots,

From our perspective, it's a semi-parasite

Mistletoe is a semi-parasite because it extracts water and minerals from the host tree using special organs called suckers. This distinguishes it from completely autotrophic plants, which produce all the nutrients they need on their own. However, unlike complete parasites, mistletoe has green leaves containing chlorophyll and is capable of photosynthesis. In the process of photosynthesis, it produces glucose from water and carbon dioxide, which is its main source of energy. For this reason, mistletoe is classified as a semi-parasite. It takes ready-made mineral substances from the host tree, but produces organic compounds itself. However, it should be noted that in certain situations mistletoe may have a negative impact on the host tree. Especially during periods of drought, when the demand for water is high, the mistletoe’s absorption of water may weaken the tree. Additionally, mistletoe can be an indirect host of pests and diseases that can be transmitted to the host tree. Despite its potential negative impacts, mistletoe also plays a positive role in the ecosystem. It provides shelter and food for many species of birds and insects.