Poison oak is a woodland shrub that is laden with a rash-causing poisonous oil called urushiol. The plant has compound leaves that contain three leaflets that vary in size, shape and color. Poison oak cannot be cut down to be removed from landscape because the plant will resprout from the roots. The typical means for removing the plant, digging up the roots, may be complicated if it sprouts in a twining plant such as ivy. Instead, you may wish to paint a systemic herbicide onto the leaves of poison oak to kill the plant.
Purchase a systemic herbicide from a garden center. Consult with a garden center employee as to which herbicide is most effective for poison oak. Common herbicides effective for poison oak include glysophate and triclopyr. Glysophate is most effective in late summer and fall, while triclopyr works best in early spring.
Place plastic drop cloths over ivy and around the poison oak to prevent accidental transmission of systemic herbicide onto the ivy.
Put on protective clothing and breathing protection before touching poison oak or handling systemic herbicide. Making sure all of your skin, including your face, is covered is wise.
Mix the herbicide according to package directions. Some herbicide brands come pre-mixed, but if yours does not, then read the directions on how to mix.
Apply a small amount of the herbicide to a sponge applicator. Paint the leaves of the poison oak plant with the systemic herbicide. Do your best to avoid the ivy.
Observe the plant, and re-apply systemic herbicide as needed to kill the plant. Plants typically die within eight to 10 days.
Dig out the poison oak's roots with a garden trowel after the poison oak has died. All parts of the plant, including the root, contain urushiol, so you must be certain to wear protective clothing and gloves when handling the roots. Bag up all refuse and discard.
Apply herbicide to plant sprouts that re-emerge after sprouts reach 10 inches in length. These will spring up from any roots that were not removed or killed by poison. Once these have died, dig them up with a garden trowel and discard them as well.