The Deadly Mistletoe

There are many reasons that trees decline in health. One of those reasons is due to organisms that live within trees as either pests or parasites.

Pests and parasites are from two different kingdoms, one the animal and the other the vegetable. The animal kingdom contains insects – insects from all types and sizes, ranging from king-size larvae to microscopic mites. In the vegetable kingdom lives fungi, bacteria and viruses that harm trees. These are all primitive plant forms, with the exception of that lovely parasite, the mistletoe. As lovely as society has made the mistletoe around Christmas, it is one of the deadliest invaders of all.

The mistletoe establishes itself on a trees living tissue through tiny rootlets that have the power to dig in to the skin of the tree like fangs. It finds itself in the tree due to the fact it creates these beautiful waxy berries that birds love, which in turn are carried by them and dropped into bark crevices of other trees. Here these berries germinate under the protection of their own gum. Mistletoe cannot live in soil but must steal its nourishment from a host tree’s sap veins.

As the mistletoe fastens on to its host, the tree begins to swell. No amount of chopping, short of limb amputation, can eradicate a mature mistletoe. Small infested limbs can be removed by pruning. This is one of the more effective control methods. Cut limbs at least 12 inches below the mistletoe. Cuts that are made immediately below the stem of the mistletoe, may leave some of the root system. The remaining haustoria will develop a new top. Mistletoe also grows on large limbs or the tree’s trunk. When growing on a large limb or trunk, remove only the mistletoe. Do not try to scoop out a portion of the host when removing the plant. If a portion of the wood is removed in an attempt to remove the mistletoe roots, the structure of the limb or trunk is weakened and is more susceptible to breakage due to wind or ice accumulation during the winter months. Wood rotting and canker fungi use the cut as an entry point.

The death is slow and painless to the tree. The mistletoe, which loves all trees, can slowly decay everything from elms, hackberries, walnuts, gums and mesquites to mere skeletons. Trees vary in susceptibility to the parasite. Cedar and juniper are not bothered by this plant and pecan, live oak and magnolia trees are seldom infected with mistletoe.

How does one protect their tree from the deadly mistletoe? There may not be anything one can do. Many things have been tried. Herbicides such as Round Up, 2,4,D, Paraquat, MSMA and DSMA have been evaluated in field trials and conducted by members of the Texas Agricultural extension but these were not effective. They also caused injury to the tree. A commercial product called Florel has been approved by the EPA recently. It contains an ethylene compound. Ethylene is a natural occurring plant hormone that increases during fruit ripening. Florel is applied during the winter months and is said to kill the the top but by later summer, new growth is observed breaking through the bark of the limb. The problem with this chemical, as with many chemicals, is that it can drift and expose other trees and plants which can cause leaf shedding.

Another method is to kill the mistletoe before it goes to seed and is transferred to other plants or trees. Mistletoe takes two to three years to reach maturity. If the plant is removed before then, you can keep it from seeding.

When selecting a tree for the landscape, check with a local arborist, nursery or County Extension Agent for trees that are adapted to your area and do not have a major problem with mistletoe.

About the Author: Andrew Johnson is the owner of Central Texas Tree Care, a leading provider of Austin tree services in Central Texas. Certified ISA Austin arborist services including: tree trimming, tree removal, tree care and stump removal. For more information on Austin tree service please visit https://www.centraltexastreecare.com.

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