Question: Now that my oak trees have dropped their leaves, I’ve noticed that they seem to be covered with mistletoe. Is this harmful to the trees, and if so, what can I do about it?
Answer: Long associated with the Christmas tradition of stealing kisses under a doorway where a red-ribboned sprig of mistletoe is hung, mistletoe has an interesting past.
Regarded by the Greeks as a cure for everything from menstrual cramps to spleen disorders and by the Celts as an aphrodisiac and fertility herb, mistletoe was also found in ancient Norse mythology.
Stealing kisses under the mistletoe became a tradition in the 18th century, where it became a common practice among British servants at Christmas time before it spread to the middle classes. Young men had the chance to kiss any girl who happened to be standing under the hanging sprig, and refusing was considered bad luck.
Another tradition entailed plucking one berry for every kiss until all the berries were gone at which time the smooching ceased. (I’m sure when selecting mistletoe, those with the most berries were the preferred choice!)
Mistletoe is actually considered hemiparasitic because, although stealing water and nutrients from the tree, the mistletoe’s leaves produce their own chlorophyll and can photosynthesize. Mistletoe attaches itself to the tree by penetrating into the tree’s growth rings with its specialized root system called haustoria. The American version of mistletoe, Phoradendron flavescens, can be found in such deciduous trees as oak, cherry, sycamore, apple and red maple.
“Phoradendron” in Greek means “thief of the tree,” which fits its beginnings as a sticky seed that hitchhikes to a new host tree on a bird’s beak or feather or on mammal fur. The common name, “mistletoe,” comes from the Anglo-Saxon word for dung — “mistel.” “Tan” is the word for twig, and thus mistletoe means “dung-on-a-twig.”
The white berries, which ripen in early winter, are relished by birds, digested and the seed is thus coated with a sticky film. Because birds not only rely on the berries for food but also use it for shelter and nesting, you can deduce that areas where there are trees heavily infested with mistletoe have a healthy bird population as well.
Once attached to the bark of the host tree, the seed germinates and grows through crevices in the bark, taking several years to grow into a flowering plant that reproduces.
Mistletoe is most commonly found on trees that are already weakened due to drought, storm damage or other pathogens, so the presence of the parasite may indicate the tree is stressed already. Since mistletoe spreads relatively slowly, it is not considered an immediate threat to a tree’s health. A few plants on a healthy tree can be tolerated well, however, trees that are heavily infested may become less vigorous, stunted and possibly die if the tree is also stressed additionally by drought, root damage, insect infestations or disease.
Pruning trees that have limited infestations during the winter can be a safe and effective way to rid the tree of mistletoe. Note that simply cutting the mistletoe back flush with the branch will not kill it, so you must prune out the infested branches.
It may be worthwhile to hire a certified arborist to diagnose and recommend proper treatment. In the case where too many branches would have to be removed, it might be better to just let nature take its course and leave it alone. In such cases, the cure may be more harmful to the tree than the parasite.
Provide your trees with extra water during a drought, mulch underneath the tree if practicable as well as adding an annual spring application of a slow-release or organic fertilizer.
If you want to harvest your mistletoe to bring indoors for the Yuletide celebrations, place it carefully out of reach of pets or children as the white berries and leaves are poisonous. The berries when ingested may cause stomach and intestinal irritation along with diarrhea and lowered blood pressure.
So enjoy the holidays, and don’t pass up the chance to grab a Christmas kiss under the mistletoe.