 |
Mistletoe in a tree, above.
Mistletoe berries, below. |
 |
Mistletoes are parasitic plants
of trees. There are thousands of different species of mistletoe
divided into the true mistletoes - American and European
species, Phoradendron spp. and Viscum spp. - and dwarf
mistletoe, Arceuthobium spp.
Mistletoes take water and
nutrients from the plant they grow on, but also produce some
chlorophyll and draw energy from the sun. About one year after
the mistletoe plant has infected the host, it will begin to
produce the foliar parts of the plant. The mistletoe plant grows
larger, producing a branched, golden-colored woody stem and
yellow-green to dark green leathery leaves. The chlorophyll of
leafy mistletoes is functional and photosynthesis is sufficient
to supply all of their carbon needs.
In mid-autumn small, round,
pearl-like berries form and these enlarge to maturity in early
winter. After they are mature, birds eat the berries and the
seeds are carried away to begin new infections or the berries
simply break off the plant and fall to lower branches to
initiate new infections on the same tree or on under story
vegetation.
Leafy mistletoe plants are
perennial and remain alive within their respective host until
the tree host, or the branch upon which it is established, dies.
Leafy mistletoes only need to extract water and mineral
nutrients in the water from their hosts. Mistletoes can only
live and reproduce on a living host, however they do not
necessarily cause a debilitating nutritional drain to that host.
A single infection on one branch, or only a few infections on an
otherwise vigorously growing tree, seems to cause no noticeable
harm to the tree. Often, though, that portion of a branch beyond
the point of a single infection may become stunted in growth or
die prematurely. Rarely, and only if multiple infections occur,
(hundreds on a single tree), there may be significant stress to
the host tree or kill it. Stressful conditions can allow
secondary diseases and insect infestations that can cause
premature death.
Treatment
The leafy mistletoes are generally not considered a serious
enough threat to warrant the need for control measures.
Exceptions might include fruit orchards, intensively managed
plantations, or historically valuable or visually important
specimen trees. There are about a dozen species of
Phoradendron in the U.S. They occur mostly on hardwood tree
species, but some also occur on juniper, cypress, and incense
cedar. Phoradendron flavescens attacks pecans in Florida,
citrus in Texas, and walnuts and persimmons in California.
Phoradendron juniperinum libocedri and P. bolleanum
pauciflorum cause significant losses on incense cedar and
white fir in California.
Physical removal by cutting out
infections of leafy mistletoes is warranted in some situations.
Care must be taken to remove all of the infection in the branch
as any living mistletoe tissues that remain are capable of
regenerating into whole plants. The cut branches do not have to
be burned or destroyed because the mistletoe plants die quickly.
History and the Mistletoe
Myth
Pliny the Elder (23-79 B.C.) may have been the first to record
detailed descriptions of the attitude of some people toward the
mistletoe. He recorded the widely held belief that whatever grew
on the sacred oak was sent from heaven. Since mistletoe was only
occasionally found on the oak, it was cause for celebration when
it was encountered. It was believed that the mistletoe plant was
protected in some mystical sense from injury or harm. If it was
cut from the oak, it retained some of these mystical powers
which could be channeled as healing powers. However, if it
touched the ground after it was harvested, its healing powers
would be lost.
The ancient Celts, who lived in
ancient Gaul, Britain and Ireland, are among the earliest known
people to believe in the mystical powers of mistletoe. The
druids, who were the priests of a Celtic religious order,
regarded the leafy mistletoes as having mystical properties. In
the autumn, as the length of the day decreased, religious
significance was focused on the winter solstice, the shortest
day of the year. The people observed that the mistletoe plants
growing on the oaks retained their leaves while the oaks lost
theirs, perhaps seeing mistletoe as a sign of rebirth or
renewal.
When Christianity became
widespread in Europe after the 3rd century, the religious or
mystical respect for the mistletoe plant and its significance to
pagan cultures was integrated into the new religion.
It remains a mystery what may
have led to the widespread custom of kissing under the mistletoe
plant during the Christmas season. It might relate to the belief
in the effects on fertility and conception held by some pagan
cultures. The earliest documented case of kissing under the
mistletoe dates from 16th century England, a custom that was
apparently very popular at that time.
Past Pest
of the Month
|
IPM Procedural Guidelines