This is the "bare bones" time of the year when a
hike outdoors so clearly reveals fascinating plant features that
had previously been hidden from view by the leafy canopy. It was
a huge witch’s broom on a tall white pine that virtually shouted
for attention a few days ago as we drove along one of our
favorite roads.
Exactly what occasionally causes these unusual growths on
pines remains a mystery to me – previous injury, fungus, virus,
who knows? Several people, in all seriousness, asked me if they
might have seen an eagle’s nest in a pine tree. Their
description of the tree’s location quickly provided me with the
answer – only a witch’s broom that appears surprisingly
nest-like!
One of the few enormous witch’s brooms, and also the white
pine on which it grows, that I know about and frequently see on
my hikes have been in outwardly good health and condition for the
past 36 years. Unlike spruce trees that become infested with
"brooming" and which eventually kills them, a single
broom on a white pine apparently doesn’t have such an adverse
impact on the tree.
Brooming on both black and white spruces is unfortunately
quite common in some areas of northeastern, central and northern
Wisconsin. Perhaps due to its frequency and the great damage the
unusual growth can do to spruce forests, there has been
considerable study done regarding the cause.
It has been determined that a very tiny parasitic plant, the
dwarf mistletoe, is the culprit that grows on the twigs,
eventually producing wounds that completely change the growth
characteristics of the infected part of the tree and eventually
the entire plant. Gradually the rate of growth of the branch on
which the mistletoe has invaded becomes so thick and bushy with
extremely rapid-developing twigs that it literally grows the tree
to death, much like a cancer.
Unfortunately once even a small bushy witch’s broom has been
discovered on a spruce tree you can be assured in most cases
that, because the "infection" is systemic, the tree is
doomed. Left to its own rate of growth, an infected spruce may
over time develop a dozen or more brooms on it.
Now is the time of the year that I hike our Houby Hill Woods
searching for brooming on the serviceberry trees. Several years
ago I sent an entire 15-inch-wide, dark brown, bushy broom from
one of our infected trees to Mary Francis Heimann, O.S.F., Senior
Outreach Specialist and expert on fruit tree diseases for the
University of Wisconsin Extension in Madison.
She was quick to identify the infecting agent as a fungus,
Apiosporina collinsii (a-pee-o-spo-RYE-na
co-LIN-see-eye). In addition to her identification she also
produced a microscope slide of several phases of the infecting
process. It was she who suggested the term "brooming"
be used rather than "witch’s broom" because, as she
said, "Some ladies feel that "witch’s broom" is a
too sexist a description." (I detected a distinct smile
between those words of her letter!)
What I do know from a rather extensive personal survey of our
county is that brooming is gradually doing away with the
beautiful serviceberry trees. If only EVERY property owner would
by law be responsible for removing and burning the existing
brooms on their serviceberry trees these incredibly beautiful
native trees, also very important to wildlife, would stand a much
better chance of survival. Sister Heimann thinks that the fungus
spores are spread primarily by wind, splashing rain and possibly
by birds, and that removing and burning the brooms will
unquestionably slow down the spread of this terrible infestation.
Another form of fungus infection, referred to as "black
knot," also stands out like a sore thumb in winter. They
are especially common on wild chokecherry and black cherry trees.
These highly conspicuous black, knobby growths, usually a half to
an inch wide and four to six inches or longer, are often fairly
close to the ground and can be easily reached and pruned from the
young trees and shrubs. Interestingly the scientific name of
black knot is Apiosporina morbosa (mor-BOE-sa), the same
genus as that of the serviceberry fungus, and it also has a very
descriptive and "morbid" species name.
Plant skeletons, ranging in size from small weeds to towering
trees, decorate the winter landscape providing food for wildlife
and great beauty for our enjoyment. Humans reap tremendous
benefits from the native plants that grow in their areas.
Ideally privileges should be properly balanced with
responsibilities. It should be up to all property owners to work
hard to become better stewards of their land, the least we can do
in thanks for enjoying the rich bounty of nature.
A tall white pine is decorated by a gigantic
"witch's" broom – appearing like the size of an eagle's nest.
Also see:
This column appeared in the Door County Advocate
on 01/05/2001.
© Copyright 2001 Roy Lukes. All rights reserved.
