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POISON IVY: LEAVES OF THREE, LET IT BE

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by William Johnson
One topic I have yet to discuss in this column is poison
ivy. Poison ivy is abundant in urban, suburban
and rural landscapes in addition to parks and other
areas. Gardeners often come into contact with poison
ivy and many contract a bothersome rash as a
result. It pays to be able to identify and avoid it.
Poison ivy contains urushiol oil and its potent stuff.
Just one billionth of a gram is enough to cause a
rash. Urishiol is also a very stable oil. Urushiol can
remain stable on an axe handle or other tool for several
years and still be able to cause a rash.
The rash (an allergic contact dermatitis) can be
caused by direct contact with urushiol by touching
the plants or by indirect contact with the plant oil that
may have contaminated a pet’s fur, gardening tools,
clothing, or other surfaces.
We typically think of this plant as lying deep in the
woods, but in fact it’s most commonly found in less
remote areas: the edges of your backyard, the shoulder
of a highway, even a sand dune on a beach or
along walking paths in parks. This plant can snake
up a tree, creep along a fence, sprout through the
cracks of a sidewalk, and grow low as a shrub. This
character is definitely a Jekyll and Hyde in the landscape.
Recognizing Poison Ivy: Poison ivy is a tall, climbing
vine that drops its leaves (deciduous) in winter. As
it climbs tree trunks, wood fences or other flat structures,
the stem produces many small roots that cling
to the surface. This is a good identifiable characteristic
of the vine in case you can’t easily see the leaves.
Poison ivy has a characteristic compound leaf consisting
of three leaflets—hence the saying, “Leaves
of three, let it be.” Mature leaves are 2 to 4 inches
long and dull or glossy green with pointed tips.
New seedlings of poison ivy are easily overlooked.
They may have a reddish tint to their foliage and will
appear upright. As they get older they will begin to
vine and grow up nearby shrubs or trees. It is easy
to come into contact with young poison ivy seedlings
when weeding flower beds, so you need to be observant.
Controlling Poison Ivy: In controlling poison ivy,
one of the most important things to do is to periodically
check your landscape carefully for seedlings or
vines. Look for the three-leaflet leaves in out-of-theway
areas, under shrubs, along back fences and by
trees.
Three methods can be effective in eradicating poison
ivy in landscapes.
The first is hand pulling or digging it out when the
soil is moist; getting out as much of the roots as possible.
Use long-gauntlet, rubber gloves available at
local hardware stores or use dishwashing gloves
when handling the vines and wear a long-sleeved
shirt. Place the plants into a plastic bag, seal it (in
consideration for trash collectors).
The second method is to carefully spray the foliage
with a systemic herbicide. This is only possible
when the spray will not get on the foliage of desirable
plants. If needed, nearby desirable plants can be
covered with plastic sheets or bags to protect them
while you do the spraying. Be sure to wet the foliage
of the poison ivy vine thoroughly with the herbicide
spray.
Systemic herbicides are absorbed by the foliage
and enter the plant’s “circulatory system”, sending
the material into the vine’s roots and killing them as
well. Glyphosate (Roundup, Eraser, Hi-Yield Killzall
and other brands) or triclopyr (Brush-B-Gon, Brush
Killer and other
brands) are
commonly recommended
for
poison ivy control.
Once the
vine dies it may
be removed.
The dead leaves
still contain the
rash-caus ing
oil and should
be handled
cautiously with
gloves.
The third
method of removal
is for larger,
established
vines growing
up in trees or
intertwined in
shrubs. Spraying
the vine foliage
is not practical in these situations because of
the potential to injure desirable trees and surrounding
landscape plants. Poison ivy control in sensitive
areas can best be achieved by the cut-vine method.
Cut off the vine a few inches from the ground with
loppers and immediately treat the surface of the
freshly cut stump with undiluted triclopyr (Brush-BGon,
Brush Killer, Greenlight Cut Vine and Stump
Killer and other brands). The vine in the tree or shrub
will die because it has no root system. The treated
stump will die because the herbicide gets absorbed
by the freshly cut surface and translocates to the
roots. Applying the herbicide to the fresh cut is necessary
because it prevents the stump from re-sprouting.
This method is very effective and may be used
any time of the year.
Getting poison ivy off your property will probably
take repeated herbicide applications. Watch out for
this unwelcome plant and be prompt and aggressive
in your efforts to control it.
William Johnson is a horticulturist with the Galveston
County office of Texas A&M AgriLife Extension
Service. Visit his website at aggie-horticulture.tamu.
edu/galveston/index.htm.

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