Mistletoe

True mistletoe (principle kind found in the United States, known as Phoradendron) is a parasite that infects thousands of trees every year.  Mistletoe obtains its water, mineral nutrients, and small amounts of organic compounds carried in sapwood from the stems of woody plants.  Mistletoe develops well in full sunlight high in the crowns of large trees.  These parasitic plants are most visible in the winter when they are actively growing and their host, the tree, is dormant.

The initial infection usually occurs on a small branch and is followed by multiple infections on the same tree after the initial parasitic plant produces fruit.  If multiple infections are present, the host usually suffers loss of vigor, dieback of branch ends beyond the attachment, and occasionally death.  Although nearly all trees are susceptible to this parasite, mistletoe is most frequently seen on elms, ashes, hackberries, water oak, and old or weak trees.

Unfortunately, mistletoe is difficult to control completely, but the parasite can be managed by using a couple of different strategies.  Removing infected branches at least one foot below the mistletoe shoots can be used to remove most mistletoe from the tree.  Mistletoe shoots on large limbs or trunks may be cut or broken off.  This reduces the mistletoes demand for water, but it must be done repeatedly because new sprouts will grow where the old were removed.  Treatment with certain specialized plant growth regulators while the host is dormant has also proved effective for control of mistletoe.