How to Remove Mistletoe
Broadleaf mistletoe (Phoradendron macrophyllum) is an evergreen parasitic plant that grows on a number of landscape tree species. Leafy mistletoes have green stems with thick leaves that are nearly oval in shape. Evergreen clumps of mistletoe are readily observed on deciduous trees in winter when leaves are off the trees.
Mistletoe berries are very attractive to birds that feed on and digest the pulp of the berries, excreting the living seeds that stick tightly to any branch on which they land. After the mistletoe seed germinates, it grows through the bark and into the tree's water-conducting tissues. Initially, the parasitic plant grows slowly; it may take years before the plant blooms and produces seed. Old, mature mistletoe plants may be several feet in diameter, and on some host species, large swollen areas develop on the infected branches where the mistletoe penetrates. If only the visible portion of the mistletoe is removed, new plants often re-sprout.
Broadleaf mistletoe absorbs both water and mineral nutrients from its host trees. Healthy trees can tolerate a few mistletoe branch infections, but individual branches may be weakened or sometimes killed. Heavily infested trees may be reduced in vigor, stunted, or even killed, especially if they are stressed by other problems such as drought or disease.
For treatment of existing trees the most effective deterrent is to remove mistletoe before it produces seed and spreads to other limbs or trees. Mechanical control through pruning is the most effective method for removal. Growth regulators provide a degree of temporary control but repeated applications are required. Using thinning-type pruning cuts remove infected branches at their point of origin or back to large lateral branches. Infected branches need to be cut at least one foot below the point of mistletoe attachment in order to completely remove it. Done properly, limb removal for mistletoe control can maintain or even improve tree structure. Severe heading (topping) is often used to remove heavy tree infestations; however, such pruning weakens a tree's structure, and destroys its natural form. In some cases it is best to remove severely infested trees entirely because they are usually a source of mistletoe seed.
Mistletoes infecting a major branch or the trunk where it cannot be pruned may be controlled by cutting off the mistletoe flush with the limb or trunk. Then wrap the area with a few layers of wide, black polyethylene to exclude light. Use twine or tape to secure the plastic to the limb, but do not wrap it too tightly or the branch may be damaged. In some tree species callus tissue will form under the plastic, further weakening the limb. Broadleaf mistletoe requires light and will die within a couple of years without it. It may be necessary to repeat this treatment, especially if the wrapping becomes detached or if the mistletoe does not die.
Simply cutting the mistletoe out of an infested tree each winter, even without wrapping, is better than doing nothing at all. Even though the parasite will grow back, spread is reduced because broadleaf mistletoe must be several years old before it can bloom and produce seed.