MISTLETOE ADVISORY

The Coarsegold Chamber of Commerce would like to remind our citizens that oak trees make a significant contribution to the charm of our area and that we are in danger of losing many of these trees. The Chamber would like to urge landowners to take steps to eradicate mistletoe whenever and wherever possible. To help in this task, we have assembled the following information.

Mistletoe is an evergreen parasitic plant that grows on many of our oaks. It has green stems with thick leaves that are nearly oval in shape. Plants often develop a rounded form up to 2 feet or more in diameter. The small, sticky, whitish berries are produced from October to December.

Mistletoe plants are either female (produce berries) or male (produce only pollen). The berries of the female plant are small, sticky, and whitish; they are very attractive to birds. The birds 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, where rootlike structures called haustoria develop. The haustoria gradually extend up and down within the branch as the mistletoe grows. Initially, the parasitic plant grows slowly; it may take years before the plant blooms and produces seed. Mistletoe has succulent stems that become woody at the base. 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 the visible portion of the mistletoe is removed, new plants often resprout from the haustoria.

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.

The most effective way to control mistletoe and prevent its spread is to prune out infected branches. 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 embedded haustoria.

Mistletoe 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. 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. There is also a growth regulator that may be used. Check with your nursery or tree specialist.

For an information page listed on the UC Davis website, visit THIS LINK.