Portland area arborist strategy for mistletoe control

Mistletoe Control & Removal

Afterward, if you enjoy forests and trees, see Giant Redwoods

First, if you just discovered that your trees have mistletoe, don't panic. It's not a crisis. Learn about mistletoe and form a maintenance plan. Plan and act; don't panic and react. It's understandable that mistletoe removal is not practical for some people. Many trees have survived for centuries with mistletoe growing nearby, and trees can reproduce. Select a mistletoe plan that fits your needs.

Mistletoe can be compared a little bit to termites. When some people discover termites in their home, they panic as if the termites were devouring with the speed of a mighty chainsaw. The termites are doing some damage, but it's happening so slow that it's worth waiting a few extra days to learn and choose the right methods or best companies to help with eradication. With mistletoe, it's presence is even less critical than that of termites. A few extra days or few extra months may be worth the wait to get the best care for your trees.

Most of the broadleaf evergreen mistletoe that you see in Jackson County is an evergreen parasite plant that grows on a number of trees in the county and city. It can be seen all the way from Medford, to Jacksonville, especially in the country like Applegate Valley or near the national forests.

Many local residents know what mistletoe looks like – most of it growing above ground on the branches of trees. If you are unfamiliar with mistletoe, it can be recognized in most cases as the small to medium size green plants with foliage that does not seem to belong on the desirable host plant or tree.

Hosts of broadleaf mistletoe include oak and other trees. One of the main trees affected in Jackson County are the oaks.

Leafy mistletoe has green stems with thick leaves that are nearly oval. Plants often have a rounded form up to 2 feet or more in diameter – almost like bushy ornaments. The small berries are produced from October to December. The clumps of mistletoe are easily seen on deciduous trees in winter when leaves are off the trees.

Mistletoe plants are dioecious. That means a plant is either a female that can produce berries, or a male plant that can produce pollen. A monoecious plant or tree has both math and female reproductive parts on the same tree. So Mistletoe is not monoecious, but is a dioecious plant.

Berries of the female plant are small, sticky, whitish, and very attractive to birds many birds. The birds eat and digest the pulp of the berries, later excreting the living seeds. (Since this is not a government or college publication, we can confidently say that “excreting” means “pooping”).

The seeds can stick tightly to any branch that they fall on. In many cases, the initial development of the infestations occurs on large trees: old trees. That’s because birds frequently prefer to perch in the top of tall trees.

A more dense population of mistletoe often occurs on an infested tree because birds are attracted to the berries of Mistletoe on that tree, where they spend more time feeding. Seeds from Mistletoe attached in the top of the tree may fall onto lower branches of the tree, producing new infestations at the lower level of the canopy.

The speed or rate of mistletoe spread to young or newly planted trees can be increased by how close they are to infested trees as well has how much Mistletoe the infested trees have. Another factor will be how many birds are flying back and forth.

After mistletoe seeds germinate, they grow through bark into the tree's water-conducting tissues. Root resembling structures called haustoria develop. Those haustoria gradually extend within the branch as the mistletoe grows. Initially, mistletoe grows slowly; sometimes needing several years to bloom and produce seed.

Broadleaf mistletoe has succulent stems that become woody at the base. Mature mistletoe may develop and become several feet in diameter. Sometimes, the host plant the mistletoe grows on will develop a big swollen looking area near the point of attachment or penetration into the bark and tissue.

When mistletoe is cut and removed from the host plant or tree, new mistletoe plants can resprout from the haustoria (the root-like growth within the the host tree’s tissue). and on some host species, large swollen areas develop on the infected branches where the mistletoe penetrates. If the visible portion of the mistletoe is removed, new plants often resprout from the haustoria.

Broadleaf mistletoe absorbs water and nutrients from host trees. Healthy trees can tolerate a few mistletoe plants, but branches may be weaken or die. Heavily infested trees may be stunted; even killed. The potential for harm to the host tree can be increased by drought or additional stress by other factors like insects or compaction of the soil.

For trees that already have mistletoe, its important to remove mistletoe before it produces seed and spreads to other limbs or trees. Mechanical control through pruning is the most effective safe methods for removal. Chemical growth regulators provide some temporary control but with multiple repeated applications. We promote the manual method of cutting. Severely infested trees can be removed and replaced with less susceptible species. Or it’s possible to plant the less susceptible species first, then remove the infested trees a few years later in the new trees don’t need to be in the same exact location.

The most effective way to control mistletoe is to prune out mistletoe or infected branches as soon as the parasite appears (that’s the “perfect world” strategy. If you can’t do it or afford it right away, then all you can do is plan and prepare for the day that it is feasable). Remove infected branches at their point of origin, or back to another lateral branch. Infected branches need to be cut at least one foot back (away) from the point the mistletoe is attached at, to completely remove embedded haustoria. Proper mistletoe control can even improve tree structure if it needed pruning anyway. If the position of the mistletoe leads you to believe that you’ll have to top the tree, consult a trained pruning specialist or arborist for help and solutions. The tree’s size may require professional help anyway.

If you have a comfortable bank account and can afford to have mistletoe removed every year or two, consider having the mistletoe cut, but not branches that it was attached to. Some people may choose to remove only the mistletoe because their tree will look unsightly if limbs are removed. That is understandable. Most people like nice looking trees; nicely formed trees.

Mistletoe infecting a major branch or the trunk may be controlled by cutting off the mistletoe. It’s been suggested by some universities to wrap that removal cut area with black plastic to stop light from reaching the remnant of embedded mistletoe. Tight wrapping was not recommended. We recommend even limiting the layer or layers of black plastic to a PATCH rather than a wrap. If the bark is thick, small staples could be used to anchor the plastic instead of a rope, twine or tape. A patch could also be made from black rubber pond liner – maybe just a scrap leftover from a pond installation or a fragment purchased from a pond store that sells liner by the foot. The liner is stronger and more durable than black plastic. If the covering can be left loose to stop light but not ventilation, that would be best. Broadleaf mistletoe will die after a couple of years without light. You can skip covering the cut and re-cut any mistletoe that grows again. If you do cover the cut, if two years of preventing light does not stop the mistletoe, what further need is there to have trees adorned with black plastic patches? Of course, you could spray paint the outside of the plastic or rubber with a grey or brown color to camouflage it.

Just cutting mistletoe each winter or two without wrapping is better than nothing. Even though the parasite return with renewed growth, spread is reduced because broadleaf mistletoe must be several years old before it can bloom and develop seeds.

Some tree species apparently resistant to mistletoe include Bradford flowering pear, Chinese pistache, crape myrtle, eucalyptus, ginkgo, golden rain tree, liquidambar, sycamore, redwood and cedar. But in Jackson county, oak is the primary tree that is infested. Most other trees are better choices. In can be unrealistic and extreme to avoid any tree ever known to be infested by mistletoe. If your choice is to retain the “native” landscape look of Jackson County, you can still plant oaks. They may not become infested or you may be able to maintain control of future mistletoe. Oaks can even be replenished every few decades. Unless the county or city makes a law against a tree, the decision lies with you or an arborist you hire for consultation.

An effective mistletoe control program in a community requires the combined effort of homeowners, businesses, the local government and public agencies. One person can control their own mistletoe, but their trees can be affected by trees that other people have. Most cities in areas with mistletoe have substantial resources and personnel trained for infestation control. That means that you will probably not need to keep an eye on the city or parks bureau very much. In fact, they probably already have an eye on the residential locations and frequently have brochures and web sites for homeowners to utilize.

If a city or neighborhood wants no mistletoe in their neighborhood, at all. Then the entire neighborhood will need trees that don’t get mistletoe. In a new development landscaped from a bare parcel of land, that’s more feasible. In established older areas that have susceptible trees, people tend to be fond of trees that are 50 years, maybe centuries old. It may be too much of a challenge to consider a complete tree replacement program. If that’s the case, just keep up the maintenance.

Many products – of any kind – are cheaper in bulk or large quantities. Services can be like that too. Consider hiring a pruning or tree expert as a collective body – where many neighbors pool their funds for professional mistletoe removal at a reduced price (since it’s done in “bulk”).

Mistletoe is a misunderstood plant. It is only partially parasitic,Notice that the leaves of mistletoe are green; it produces some of its own chlorophyll. Therefore making some of its own food. It can become more parasitic in a drought when it takes water away from its host. Mistletoe dies if the host tree dies.