Impact

Ecological Impacts

As long as V. album L. is not present in large numbers on trees, it does not poses a lethal threat to them (Glatzel and Geils 2009. However, in the face of climate change, leading to more frequent droughts, weakening host trees and consequently increasing the role of mistletoe, which, by reducing the availability of water and nutrients (Sanguesa-Barreda et al. 2012, Mutlu et al. 2017) significantly worsens the condition of the trees during the dry summer seasons and alone or in combination with other factors (pests, diseases) increases their mortality (Iszkuło et al. 2020). This phenomenon is observed in recent years in eastern and central Europe (Kollas et al. 2018; Lech et al. 2019; Szmidla et al. 2019).

The presence of mistletoe in tree crowns affects them either directly, by shortening the life of the host plant, or indirectly, by affecting traits related to the habitat (for example, the availability of food resources). Due to the mistletoe's relatively long life span, its dependence on the host lasts for many years and can be intensified by the systematic appearance of successive individuals of the parasite on the tree (Zuber 2004; Mellado and Zamora 2017).

V. album impacts negatively its host depleting water with mineral nutrients and decreasing the photosynthetic rate of the tree (Glatzel i Geils 2009; Zweifel et al. 2012). During periods of severe drought, the stomata on the tree's leaves are closed, while the gas exchange intensity of mistletoe remains very high (Zweifel et al. 2012). This increases the host's water deficit and can contribute to its weakening (Schulze and Ehleringer 1984; Zweifel et al. 2012). Under drought conditions, the risk of death of mistletoe-infested individuals is four times higher, compared to trees free of the parasite (Geils et al. 2002). As negative effects of mistletoe infestation of trees reduction or disappearance of fruiting, defoliation, and decrease in tree growth is often observed (Becker 1986; Sönmez 2014; Iszkuło et al. 2020). In addition, wounding the branches and stems by its endophytic structures facilitates infection by other pathogens, resulting in co-infections, especially with fungi (Geils et al. 2002; Noetzli et al. 2003; Zuber 2004; Mathiasen et al. 2008). The effects of mistletoe infestation on trees are not only seen in individual specimens of the host plant, as this is a species that can affect the entire ecosystem, such as species composition and stand structure (Watson 2009; March and Watson 2010; Mellado and Zamora 2017). 

However, shrubs of mistletoe serve as a specific ecologic niche. It is a habitat for specific communities of arthropods, e. g. Cacopsylla visci, Pinalitus viscicola, Anthocoris visci (Lázaro-González et al. 2017). 60 families across 16 orders of birds are reported to nest in the shrubs of mistletoe worldwide (Cooney et al. 2006). Infections of trees by mistletoe, through defoliation of crowns, contributes to changes in light conditions, initiating the emergence of new plant species, while falling mistletoe seeds, together with the excrement of birds that spread them, increase soil fertility. In addition, reducing the content of certain substances in the needles of mistletoe-infested pines can have a positive effect on reducing the development and survival of foliar pests (Lázaro-Gonzalez et al. 2019).

In nature conservation mistletoe plays the role of a phytoindicator of contamination of the natural environment with heavy metals (Nováček and Teterová 1987; Patykowski and Kołodziejek 2016).

Economic Impacts

The negative economic impact connected with the loss of infested trees is evident. However, mistletoe has been a profitable good due to few reasons. It is a pharmaceutical plant, it is shrouded in legends and it is decorative.

Already Hippocrates (460–377 BC) recommended the European mistletoe to treat diseases in the spleen and complaints associated with menstruation (Bussing 2000). In the early 18th Century, Sir John Colbatch (1719-20) stated that mistletoe was a "most wonderful specific remedy for the cure of convulsive distempers." He referred to V. album, which has since left the realm of witchcraft, herbalism, and quackery to become an accepted pharmaceutical plant (Gill and Hawksworth 1961). Extracts of V. album demonstrated hypotensive, anticancer, antimicrobial, analgesic and anti-inflammatory capabilities, among other biological activities (Luther and Becker 1986; Vicaş et al. 2011; Szurpnicka et al. 2020, Kieszken et al. 2022). They are widely used as complementary and alternative medicines for the treatment of various neurological disorders. Lectins, viscotoxins, lignans, amines, amino  acids,  alkaloids,  polyphenols, phenolic acids, polysaccharides and terpenoids are the main active compounds (Melo et al. 2023, Vicaş  et al. 2024).

Mistletoe has been mentioned even as food for human, e.g. Australien tribes. In Europe it was used as nutritious fodder for livestock (Gill and Hawksworth 1961, Barlow 1987; Akeret et al. 2001; Hejcman et al. 2013; Kühn et al. 2013). Until the first half of the 19th century, Viscum spp. fruits were used to make a bird stick in Africa and Europe. as well as to reduce populations of harmful insects attacking young vines (Jabłonski and Szmidla 2022). In folk medicine, the Celts used mistletoe to treat various ailments as early as ancient times.   

It seems also interesting to use chemical compounds derived from the common mistletoe as an alternative methods of soil nematode control based on the toxical action of the plant extracts. Maher et al. (2021) confirmed the bioactive properties of V. album against root-knot nematode Meloidogyne incognita.

Collected shrubs of V. album are commonly commercialized in Christmas markets for decorative purposes.

Social Impacts

The most well-known social impact of mistletoe is its association with Christmas and the tradition of kissing under the mistletoe. This custom dates back to the 18th and 19th centuries. It is considered a symbol of peace, goodwill, and fertility. People often hang mistletoe in doorways during the holiday season, and the act of kissing under it has become a playful social ritual. Mistletoe is often believed to bring good luck. In France mistletoe was often given as a Porte Bonheur – a gift for luck for the New Year. Furthermore, in Britain it was associated with peace at one time, though it has become eclipsed by the kissing custom (Briggs 2022).

Mistletoe is very popular especially in regions with its high occurrence and more intensive utilization. For example mistletoe enthusiasts close to Herefordshire in Britain established annual ceremony to crown a Mistletoe Queen and have chosen 1^st December as the National Mistletoe Day (Briggs 2022).