For centuries, sweethearts have stolen kisses under the green branches and white berries of holiday mistletoe. Few of them know the plant is actually a type of parasite that draws part of its lifeblood from its tree host.
R. Jarret, UGA CAES
|MISTLETOE, though good for kissing, can harm the tree it lives in and on. Though not a true parasite, mistletoe steals water and nutrients from the tree it grows in.|
"Mistletoe is actually an epiphyte," said Jerry Walker, a plant pathologist with the University of Georgia College of Agricultural and Environmental Sciences. "It's not a true parasite, because it produces its own chlorophyl. It draws water and other nutrients from the host tree."
Walker said mistletoe's leathery green leaves contain chlorophyll that lets it make sugar carbon dioxide and water, like all other green plants.
"Its root system invades the internal tissues of the host tree, extracting water and minerals, and anchors it to the host," Walker said. "Basically, it grows on another plant at its expense."
Sharing its water and minerals with mistletoe is no problem for healthy trees. But unhealthy trees can sometimes fall to the added stress. "Weak, older and unhealthy trees are often hosts for mistletoe," he said.
The mistletoe found in the South is American mistletoe. "In the western states, they have dwarf mistletoe, which is very harmful to the host plant, especially conifers," Walker said.
Mistletoe may have gotten its link to the holiday season in part because it's so noticeable in the winter.
"You see it in trees this time of year because most of its hosts are deciduous and have lost their leaves," said Walker. "It's there year- round. You just can see it so easily now."
You see mistletoe in trees around homes and cities more often than in undisturbed forests. UGA wildlife scientist Jeff Jackson has his own theory as to why.
"Mistletoe provides birds, especially mockingbirds, one of the few winter berries around," Jackson said. "Where you see mistletoe in trees, you'll most likely see mockingbirds perched on the branches."
Jackson says mockingbirds are very territorial. They tend to make their homes in areas where humans live.
"They don't feed from your bird feeder. But they're in your yard driving other birds away," he said. "They also perch high in trees, and that's where mistletoe tends to grow."
The wind and several bird species spread mistletoe from tree to tree. The birds feed on the white berries, roost in the treetops and deposit the seeds on the branches.
Birds aren't the only ones that benefit from mistletoe. "It's the sole host plant of an interesting butterfly called the great blue hairstreak," Jackson said. "This butterfly is in the same family as the little blue butterflies you see in the spring."
In caterpillar form, the butterfly feeds on mistletoe. "Its wingspread is a little over an inch, and the wings reflect a metallic blue when open," said Jackson. "If you want to see it in your garden, watch under the trees that host mistletoe."
Although birds and butterflies find the berries tasty, they're toxic to humans. When decorating with mistletoe, keep it out of reach of children and pets. The stem and leaves are toxic, too, and can irritate skin.
In most cases, mistletoe doesn't damage trees. However, in rare cases of multiple infections, it may. Infected branches, and even the whole tree, may die.
R. Jarret, UGA CAES
|MISTLETOE starts out as a tiny, harmless- looking plant on a tree, but can grow into a problem.|
"It's an interesting plant. But it's not desirable, unless you grow it for harvest at Christmastime," Walker said. "There are no chemicals labeled in Georgia for its removal. But you can control it by cutting it out of the trees."
Cut out infected limbs 1 to 2 feet below the infection point. If you remove only the mistletoe, it will probably regrow.
Removing infected limbs may not be easy when the mistletoe is in the treetop. "Years ago, people would shoot it out with shotguns," Walker said. "But I don't recommend that."
(Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)