When the tip of a branch
on certain trees and shrubs gets damaged, it may remove
apical dominance. This results in a tuft of small
twigs and branches from the buds that had previously
been under control by the top bud on the stem. The dense
proliferation of twigs resembles a witche's broom, thus
the name.
Witche's brooms may be
caused by a number of factors. Some insects will infest
and kill the apical bud on certain species trees and
shrubs. There are a few diseases that may also result in
this type of growth. In some cases, the cause is not
known.
The twigs that develop on
a witche's broom are usually poorly attached to the
branch and may break off in the wind or ice storms. Even
so, they are generally not a serious problem for the
plant. They just look bad in the dormant season.
Witche's brooms that form
on evergreen trees are often the source of some
interesting new specimens for the landscape. People will
cut off the broom and graft it to a rootstock of the
same species. This will form a unique, dwarf standard
plant that has different foliage from the mother tree
and usually stays in a dwarf form.
