Plant of the Week
Poison Ivy
Latin: Rhusradicans
As society becomes increasingly urbanized, a valuable bit of botanical
knowledge is being lost and people all over the state are paying the price for
this loss of knowledge.
Being able to identify poison ivy is an important bit of information that
every person who leaves the black top parking lot should know. Poison ivy is
found in every county of Arkansas and in almost all states except for the driest
part of the desert Southwest. Being readily spread by birds, it's as common in
flower beds and the woods.
Poison ivy (Rhusradicans), a member of the Anacardhaceae (Cashew)
family, grows as a vine with root-like tendrils that aid in climbing. It has
yellow-green leaves that are borne in a compound leaf with three leaflets. The
old adage of "leaflets three – let it be" should be taught to all children.
Leaflets are usually 3 to 5 inches long and ovate in outline with an entire
margin. In the fall, the leaves turn shades of orange or red and may produce
open clusters of buckshot size white berries on old vines
It's the only common vine plant with three leaflets other than clematis, but
clematis climbs by twisting its petioles around the support and lacks the
root-like tendrils. Immature shoots of box-elder maple often have three leaflets
on their leaves, but it grows as a tree, not a vine. Poison ivy is equally at
home in sun or shade but is more common in fertile soils than poor soils. Poison
oak (Rhustoxicarium) is similar to poison ivy except it does not climb
but instead forms small bushes 2 to 3 feet tall. The leaves are deeply lobed but
still produced with three leaflets.
About half of the population is allergic to the toxins found in poison ivy
with light-skinned individuals and young people the most susceptible groups. The
non-volatile oil causing the allergic reaction is called urushiol, which is
actually composed of four separate toxins. Urushiol is stable and will remain
active after being stored as dried plant specimens for over 200 years.
These toxins, apparently an adaptation to prevent foliage feeding by grazing
animals and insects, are released when the foliage is brushed and the epidermis
broken. Also, contact with the roots or even smoke from logs containing poison
ivy vines can cause dermatitis. Because this is a true allergic reaction, a
person does not develop symptoms on the first exposure to the plant. However,
subsequent exposures result in an allergic reaction due to the activation of our
body’s immune response system.
Symptoms, usually expressed as raised, red, itching rashes, usually appear 24
to 48 hours after exposure. Thorough washing with soap and water, even several
hours after exposure, will often prevent symptom development. Several
over-the-counter products are available for relieving the itch. Prescription
medication is also available which will make short work of the irritating rash.
Ridding the garden of this pest is imperative. Several companies sell aerosol
products for use as poison ivy killers that are effective if used according to
direction. Contact herbicides such as Roundup are not as effective against this
pest and repeat sprays may be required.
Grubbing out the roots is probably the most effective means of eradication
but is not recommended for people with hyper sensitivity skin. Winter time
grubbing is less likely to cause dermatitis as long as long-sleeved clothing is
worn and gloves used.
By: Gerald Klingaman, retired
Extension Horticulturist
- Ornamentals
Extension News -
July 18, 2003
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