Mistletoe is a hemi-parasitic plant that attaches itself to host trees, posing a serious threat to their overall health and structural integrity. This evergreen shrub is often noticed during winter when deciduous tree leaves have fallen. Because mistletoe embeds itself directly into the tree’s vascular system, simply removing the visible plant material is not enough to eliminate the infestation. Protecting the tree requires specific methods to fully eradicate the parasitic growth.
Identifying the Parasite and Assessing Tree Damage
Mistletoe is easily recognized by its dense, woody clusters of leathery, green leaves, which stand out on the bare branches of deciduous hosts like oaks, maples, and sycamores. The plant produces small, waxy, white or pink berries that are sticky and contain the seeds for new growth. Although it uses its own leaves for photosynthesis, this hemi-parasite taps into the host tree for water and mineral nutrients.
The most damaging component of the plant is the haustorium, a specialized root-like structure that penetrates the host’s bark and integrates into the xylem, the tree’s water-conducting tissue. By diverting water and nutrients, the mistletoe weakens the branch, leading to stunted growth, dieback, and swellings on the branch. A severe infestation significantly stresses the host tree, making it more vulnerable to drought, insects, and disease, potentially leading to the tree’s decline or death.
Techniques for Physical Removal and Pruning
Physical removal is the most effective method for controlling light to moderate mistletoe infestations. Simply cutting the visible plant at the surface of the branch provides only temporary relief, as the embedded haustorium remains alive and will quickly sprout new growth. To achieve permanent removal, the section of the host branch containing the haustorium must be completely cut away.
Prune the infested branch at least 12 to 18 inches below the visible point where the mistletoe attaches. This distance ensures that the entire root-like structure is eliminated. When dealing with larger branches, proper pruning techniques, such as the three-cut method, should be used to avoid tearing the bark of the main limb or trunk.
For light infestations involving only small, outer branches, homeowners can manage the removal themselves with standard pruning equipment. If the mistletoe has established itself on a major structural limb or the main trunk, or if the infestation is widespread, a certified arborist should be consulted. Removing too many large branches at once can compromise the tree’s structure and health, particularly if it leaves the tree with insufficient foliage for photosynthesis.
If the infestation is located on a large limb that cannot be removed without damaging the tree’s structure, an alternative technique is to repeatedly cut the mistletoe flush with the branch surface. After cutting, the area can be wrapped with black polyethylene plastic or painted with black latex paint to exclude light for several years. This light deprivation attempts to kill the haustorium, but it is not always a permanent solution and may be aesthetically unappealing.
Chemical Control Options and Application Timing
Chemical control methods offer an alternative, particularly for infestations in the high canopy or on large, inaccessible limbs where pruning is not feasible. The most common chemical treatment involves using a plant growth regulator containing ethephon. Ethephon works by releasing ethylene, a natural plant hormone, which causes the mistletoe shoots to separate from the host branch.
The ideal time for ethephon application is during the host tree’s dormant season, typically in late winter or early spring, before the host tree begins to grow new leaves. This timing allows the chemical spray to thoroughly wet the mistletoe foliage without being intercepted by the host tree’s leaves; daytime temperatures above 65°F are often required for best results. Chemical control only causes the visible mistletoe plant to die and fall off; it does not kill the embedded haustorium.
Since the parasitic root structure remains alive, the mistletoe will eventually regrow, requiring repeated chemical applications every few years. Chemical control only eliminates the visible portion of the plant, leaving the dead, woody material to decay naturally or requiring subsequent physical removal. Due to the need for thorough coverage and the potential for improper application to damage the host tree, chemical treatments are best performed by experienced professionals.
Long-Term Prevention and Tree Health
Effective long-term management relies on regular inspection and maintaining optimal tree vigor. The parasite’s seeds are encased in a sticky substance called viscin, which allows them to adhere firmly to a new branch after being consumed and deposited by birds. Preventing seed dispersal is paramount to controlling the spread within the landscape.
Regularly inspecting trees, especially during the winter months, allows for the prompt discovery and removal of new mistletoe seedlings before the haustorium becomes deeply established. Maintaining the health of the tree through proper watering and fertilization practices plays a protective role. Healthy, vigorous trees are more resilient and can better tolerate a light infestation than trees already stressed by drought or poor nutrition.
If you have highly susceptible, high-value trees, consider applying physical barriers, such as netting, during the berry season to discourage birds from feeding and spreading the sticky seeds. For severe, recurring problems, the most effective long-term solution may involve removing heavily infested trees and replacing them with less susceptible species.