Pest/Pathogen of the Month: December
Scientific name: Approximately 1300 species distributed among five plant families e.g. Arceuthobium spp., Viscum spp., Phoradendron spp.
Common name: Mistletoe
In Nordic mythology the goddess of love and fertility, Frigg, had a premonition that her son Baldur would be killed. She went forth to obtain an oath from all object in the nine realms that they would avoid harming her son, but she overlooked mistletoe due to its small and innocent demeanour. Even though Baldur was invincible, a mistletoe dart created by the god of mischief, Loki, killed him where he stood. Today, mistletoe is considered an obligate aerial parasite of several cornerstone tree species in forestry. Berries of mistletoes are eaten by herbivores that spread the seeds through defecation, especially birds. Seeds may also be disseminated by wind or hydrostatic pressure. The seed of mistletoe is coated by a sticky substance called viscin that cements the seed and ensures the seed is not disturbed. In spring, the seed will germinate and produce a haustorium that penetrates the vascular tissues of the host plant to syphon water and photosynthetic metabolites. Leaves of the mistletoe are dark green, oval and rigid and flowers in summer may be white, yellow or red. White berries produced by this plant contain toxic compounds that are poisonous to humans and some animals. Mistletoe has been reported as a serious parasite of conifers, especially in Northern America and Europe. Infection leads to weakened trees which reduces growth and timber quality, allows for attack by insects and bole swelling at the base provides a home for decaying fungi. Infection at the crown may also impact the soil ecosystem and the optimal functioning of the ectomycorrhizal community of the tree. In the end, the tree may succumb to the combined damage of the different factors and this may lead to extensive yield losses. Mistletoes are distributed across several different plant families, however, in the Southern Hemisphere most of the species belong to the Loranthaceae and Viscaceae. Despite their fragile exterior, the oath of the mistletoe should never be treated as superfluous.
