15 , 2004
Mistletoe (Phoradendron macrophyllum) is an evergreen parasitic
plant that grows on a number of landscape tree species in
to Identify Mistletoe
Leafy mistletoes have green stems with thick leaves that are
nearly oval in shape. Plants often develop a roundish form
up to 2 feet or more in diameter. The small, sticky, whitish
berries are produced from October to December. Evergreen clumps
of mistletoe are readily observed on deciduous trees in winter
when leaves are off the trees.
Cycle and Biology
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. In most cases, the initial infestation occurs on
larger or older trees because birds prefer to perch in the
tops of taller trees. A heavy buildup of mistletoe often occurs
within an infected tree because birds are attracted to the
berries, and may spend a good deal of time feeding on them.
In addition, seeds may fall from mistletoe plants in the upper
part of the tree, creating new infestations on the lower branches.
The rapidity with which mistletoe spreads is directly related
to the proximity and severity of established infestation,
and newly planted trees can be quickly infested if they are
growing near old heavily infested trees.
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.
In newly developed areas or in older established areas where
trees are being replaced, the ideal method of controlling
or preventing mistletoe is to plant trees believed to be resistant
to mistletoe. Avoid trees like Modesto ash, known to be especially
susceptible to mistletoe infestation. Where many new trees
are being planted, control mistletoe in any surrounding infected
trees to reduce the infection of new trees. For treatment
of existing trees, it is important to remove mistletoe before
it produces seed and spreads to other limbs or trees. Growth
regulators provide a degree of temporary control but repeated
applications are required. Severely infested trees should
be removed and replaced with less susceptible species to protect