Plant Pathology Infobytes
December 1, 1998
Mistletoe - Great for the Holidays but Tough on Trees
Mistletoe has a long tradition of association with the Christmas holidays and is often used during this season to add a festive and decorative touch to many home across the United States.
But let's not forget this traditional plant is also a parasite which grows on a number of landscape trees in Mississippi and is often a source of concern to homeowners who have infected trees in their landscape.
Trees commonly parasitized by mistletoe in the South include water, willow, and red oaks, and other trees, such as pecan, hickory, hackberry, Osage orange, river birch, and green ash.
County Extension Offices are often asked if mistletoe is damaging to a tree's health. Although mistletoe has green leaves and manufactures part of its own food supply, it does depend on its host (the tree) for water and nutrients.
Most trees that are otherwise healthy can tolerate a few mistletoe crowns ; however, trees heavily infected over a period of several years often are reduced in vigor, become stunted, and are more susceptible to harsh environmental conditions, which may cause tree death.
Another frequently asked question is "How does mistletoe spread from tree-to-tree?" Mistletoe is a flowering plant and female crowns produce small, whitish berries in late fall and early winter. Seeds are covered by a sticky outer pulp layer. Birds feed on the sticky pulp and discard the seeds which stick to their bills, feet, and other body parts.
In this way the seeds are carried to other trees or other branches of the same tree and deposited, where they stick tightly. After a short time, the mistletoe seeds germinate, and the parasite grows through the bark and into the tree's water-conducting tissues, where rootlike structures develop. These "roots" gradually extend up and down within the branch as the mistletoe grows. In some cases, older, mature mistletoe plants may reach several feet in diameter.
How do you control mistletoe? The most effective method is to prune out infected branches as soon as the early infestations become apparent. Contact your County Extension Offices for the correct pruning method.
What about chemical control of mistletoe? Recent research in Mississippi with ethephon chemical growth regulator has been conducted by the Extension Plant Pathologist at Mississippi State university. Unfortunately, results of these studies indicate currently available chemicals are largely ineffective for ridding trees of this tree pest.
NOTE: While mistletoe seeds aren't harmful to birds, they are poisonous to humans, so advise your clientele to use care when this plant is included in home decorations.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.