Facts on the Mistletoe Parasite

Mistletoe Biology

• Leafy mistletoes have thick, nearly oval leaves and green stems and grow to have a rounded shape up to 2 feet in diameter. Dwarf mistletoes, or plants in the genus Arceuthobium, are smaller than leafy mistletoes, with stems growing no more than 8 inches long, small, scale-like leaves and segmented shoots. Mistletoe plants are dioecious, meaning that each plant is male or female; only the female plants produce berries. Mistletoes grow very slowly, so it may take years for the plant to grow from seed to produce berries. Where seeds land on a tree's bark they germinate and grow into the tree with root-like structures, haustoria, located in the tree's water-conducting tissue.

Mistletoe Spread

• The berries that develop on the female mistletoe plants are very attractive to birds, which tend to perch in the tops of taller trees. Once the seeds, still living, pass through a bird's digestive tract, they stick tightly to any branch they land on, eventually germinating and growing into the bark. Seeds also fall from mistletoe plants in the upper portion of the tree to infect lower branches and adjacent trees. Dwarf mistletoes spread by forcibly discharging seeds from fruits. Seeds are shot up to 40 feet horizontally.

Mistletoe and Trees

• Mistletoe plants use haustoria to absorb water and mineral nutrients from host trees. A healthy, vigorous tree can tolerate a light mistletoe infestation, although individual branches are potentially weakened or killed. Where trees are covered with a heavy mistletoe infestation, they may experience stunted growth and reduced vigor and may even be killed, especially if they are also diseased or under drought stress.

Treatment

• The only way to effectively eradicate mistletoe on a tree is to remove the entire mistletoe, including the haustoria, by cutting the infected branch off at least 12 inches below the mistletoe's point of attachment as soon as possible after the mistletoe is noticed. Repeatedly cutting the mistletoe flush with the bark on the branch or trunk will not kill the plant, but can improve the tree's appearance and prevent seed production and further spread. Cutting the mistletoe off flush with the bark and wrapping it with multiple layers of black plastic to deprive the plant of all sunlight may eventually kill it.

Interesting Facts

• The term "mistletoe" comes from the Anglo-Saxon for "twig with bird droppings." The name of one of the mistletoe genera, Phoradendron, essentially means "thief of the tree" in Greek. Throughout history, mistletoe has had various meanings and symbolic value, sometimes representing peace, love or the coming spring. Mistletoe is poisonous and should be used as holiday decorations cautiously where small children or pets are present.