Getting rid of poison oak plants starts with the positive identification of the problem plant. "Leaves of three, let them be" is the familiar warning that applies both to poison ivy (Rhus radicans) and to poison oak. Poison oak often has leaves shaped like the leaves found on oak trees (thus the common name). The leaves of both poison oak and ivy turn red in fall, and both plants produce white berries.
Like Rhus radicans, poison oak vines (or shrubs, in some cases) are indigenous to North America. The former is more widespread but does not appear on the West Coast. Meanwhile, one type of poison oak (Rhus diversilobum) grows primarily on the West Coast and another in a few parts of the East.
When working around poison oak, protect yourself with heavy gloves, a long-sleeved shirt, and long pants so that no skin will come in contact with the plants. Dispose of dug up or dead plant material in sealed plastic bags. Never compost or burn poison oak plants. Inhaling the fumes from burning poison oak plants is extremely hazardous. Poison oak remains poisonous long after it is dead, so you must dispose of it carefully.
Manual methods may be practiced at any time of the year, except during the winter in cold climates when the ground is frozen, while methods involving herbicides are best employed during the height of the growing season. Manual eradication may have to be repeated.
The simplest method for getting rid of poison oak manually is to pull it out by the roots. Make sure you dispose of all parts of the plant properly. Another manual method for getting rid of poison oak (if it is growing on the ground, rather than in trees) is to choke it out by covering it with impervious material. First, cut the plants down close to the ground, then cover the stump with a plastic tarp or other material that is impervious to light and water.
Weight down the tarp along the edges with stones, bricks, or boards. If you need multiple tarps to cover the plants, overlap the tarps by at least 12 inches and weight them down along the seam. Leave the tarp in place until the plants have died, then dig up the plants and dispose of them in plastic bags. Do not burn them or compost them.
Removal With Herbicide
Herbicides that are effective for killing poison oak include glyphosate (e.g., Roundup brand) and triclopyr (e.g., Ortho brand). You can apply herbicide to the stumps of cut plants or to the foliage of uncut plants, but both must be done while the plant is actively growing. For the first method, cut the stem one to two inches above the ground and apply the herbicide immediately, using a spray tank. The fresh wound will drink in the herbicide, transporting it deep inside where it can do its damage.
Applying herbicides to the leaves of poison oak is most effective during the flowering stage (using triclopyr) or fruiting stage (using glyphosate). Spraying the foliage must be repeated until the poison oak is fully eradicated. Follow these tips for the best results:
- Don't spray on a gusty day. Not only will you waste herbicide, but you risk having the spray blow onto your landscape plants and damaging them.
- Spray only when the plants are dry and there will be no rain for at least 24 hours. Herbicide works best when the plants are thirsty.
- Don't spray poison oak that is scaling a tree, as you could damage the tree. Manual removal may be preferable here, although you could dab (not spray) a bit of herbicide onto the individual leaves of the poison oak, so as to control the application more carefully.