Leaves of Three -
Let it Be!

Although there are many plants with leaves of three, if they are considered weeds leave them alone! Poison Ivy, Poison Oak and Atlantic Poison Oak will cause most to break out in a rash if the weeds are touched, hospitalization in extreme cases.

Poison Ivy (Toxicondendron radicans)

Older identifications are
Rhus radicans and
Rhus toxicodendron.

Poison Ivy is found more in the eastern United States. It is a woody perennial and can be a trailing vine growing in the appearance of ground cover and it also climbs up appearing to be a tree.

Photo: Melinda Fawver

This weed is found growing around water areas such as lakes, swamps and rivers as well as wooded areas. Poison Ivy can be shade tolerant, although it prefers sun and grows in different soil types, especially rich soil with good drainage.

From the main woody stem grows the petiole branch that the leaves grow from. Leaves are compound consisting of three leaflets with the center leaf usually longer. They grow from 3/4 to 4 inches wide and 7 to 10 inches long. Edges can be crinkled, slightly lobed, toothed or untoothed. They are often shiny and change colors depending on growth stage and season. Leaf colors in summer are more likely to be light to dark green and in fall colors change to bright reds, oranges and yellows.

Yellowish-green flower clusters appear May through July and grow from 2-6 stalks. Berries, or drupes, appear July through late fall and can be grayish to golden-white and about 1/4 inch big.

Once one becomes familiar with poison ivy, it's easy to recognize. Be aware as woody stems climb up trees they attach themselves with aerial roots, or roots from the stem that attach to the host tree. Recognizing these aerial roots can help for identification in winter. As the plant matures the aerial roots become very dense, even hairy or fuzzy in appearance.

Poison Oak (Toxicodendron diversilobun)

Often confused with Poison Ivy. Poison Oak grows more in the western part of the United States, which also gives it the other name of Western Poison Oak.

This can also be a vine but can also grow into a shrub. As weed grows it can smother other smaller vegetation.

Photo: Terrance Emerson

Poison Oak looks very similar to Poison Ivy because of the leaves of three. A closer look reveals duller green leaves that are usually more distinctly lobed with hairs. Leaves resemble oak tree leaves giving this weed it's name. Their colors also change from green in spring to reds and oranges late summer into fall. Flower colors are more ivory colored then turn into white-beige to greenish colored berries.

This weed also grows around water and woody areas. It also prefers sun but can grow in shade as long as it isn't extreme.

Atlantic Poison Oak (Toxicodendron pubescens)

Also called Oakleaf Poison Ivy, this cousin of the above two also shares the synonym Rhus toxicodendron with Poison Ivy.

Like Western Poison Oak, Atlantic Poison Oak grows into a shrub. It can be found in diverse settings from water to forests to dry, sandy areas. Like it's cousins, Atlantic Poison Oak prefers the sun but can grow in semi-shaded areas.

Leaves alternate are usually hairy on the bottom but smooth and shiny on top. Leaves grow about 6 inches long and are in the same leaves of three pattern. They also resemble the leaf of an oak tree.

Leaves are bright green in spring and also change color later in the fall to reds and oranges. Flowers grow in clusters then turn to fruits that are a round, yellowish-green.

These above leaves of three weeds have the same toxin called urushiol. This is a clear, sticky oil inside the plant.

When weed is bruised, damaged or rubbed, the oils transfer and produce itchy rashes to sometimes serious outbreaks on humans and other animals. Pets with a lot of hair that rub on weeds are likely to be protected. If we pet our dogs and cats, however, urushiol will be transferred to us.

All of these weeds can reproduce from seed but are more likely to sprout from from rhizomes, or horizontally creeping roots. This isn't considered an invasive plant.

Always cover yourself with long sleeves and pants when removing manually. It's best to pull weed in early spring when roots are loosely structured.
Cut or mow over any of the above weeds depleting their energy reserves. Be aware that airborne particles can cause irritation.
Post-emergents don't always work. The most effective products have glyphosate or triclopyr.
Vinegar solutions can work well at killing poison ivy.
Apply mulch. Throw away weeds - Don't compost.

Never Burn these weeds! To do so would release toxins in the air.

If weed is burned a rash can appear on lining of lungs, causing extreme pain and sometimes fatal respiratory difficulty.
Although most who get the poisonous oils on skin break out with an itchy rash for one to four weeks, worse situations can occur. Never ingest this weed or have it come in contact with eyes or mucus lining of the mouth. The digestive tract can be effected cause serious rashes too. Seek medical attention for extreme cases.
If you think you may have come in contact with Poison Ivy lots of cool running water may prevent rash from developing within an hour of exposure. Don't use alkaline products, like soap, to wash. It will spread the oils. If rash should occur calamine lotion helps to stop itching.

FYI:

These two weeds are often mistaken for Poison Ivy, but neither have leaves of three:

Poison Sumac (Rhus Vernix) is also within the Toxicondendron genus that also has urushiol oils. Poison Sumac prefers many of the same growing conditions as the above leaves of three. Poison Sumac, however, has a pinnate leaf structure, or feather-like in appearance. They have leaflets on each side of petiole but rather than only three, there are usually 7 leaflets but there can be more.
Virginia Creeper (Parthenocissus quinquefolia), which is also a vine. It can grow as high into trees as well. There are two big differences here, though. The Virginia Creeper has 5 leaves and the berries have oxalic acid, which can make humans sick. No rash comes from touching this weed.