¶ … oozing, itchy, misery-inducing rash that comes from touching a member of the poison oak family would have no doubts at all that eradicating the plant is a fine idea indeed. This paper examines various methods of poison-oak eradication as well as the reasons that controlling this plant may prove to be necessary or advisable. Among the methods that are discussed for eradication are controlled burning, mechanical control (such as mowing it), herbicide use and biocontrol - usually in the form of hungry goats!

Before beginning a consideration of the ways in which poison oak can be eradicated it will be useful to provide a brief overview of the plant itself.

Although it may surprise many people who have far-from-favorable experiences with poison oak, it is actually a member of the same genus of plants as the cashew - a far friendlier relative. Along with the closely related poison ivy and poison sumac, poison oak produces an allergic reaction in many people that tends to become worse with repeated exposures to the plant.

In fact, although poison oak, poison ivy and poison sumac are popularly considered to be separate plants, their scientific classification is a little more complex. While some scientists group poison ivy and poison oak together as varieties of a single species, other categorize them as separate species because of the significant differences in their leaves. In general, poison oak and poison ivy are considered to be variants of Toxicodendron radicans. Sometimes poison oak is classified as Toxicodendron diversilobum while poison sumac is identified as a separate species -Toxicodendron vernix.

Both poison oak and poison ivy - whether two varieties or two species - are woody, perennial plants found throughout large sections of the United States and Canada, often growing besides roads or in open fields. Sometimes the plants can be found in vine form (either trailing on the ground or supported by trees) but are most often found in the form of shrubs.

The leaves of poison oak and poison ivy - as any child who has ever gone camping will tell you - include regular groupings of three leaflets. The plants are also marked by clusters of small, pale yellow or white berries each summer and fall. Beyond these characteristics, there is substantial variation (partially seasonal) as to size, color and shininess of leaf surface.

The leaves of poison ivy are red in early spring. Later in spring, they change to shiny green. They turn red or orange in autumn. Each leaf is made up of three leaflets more or less notched at the edges. Two of the leaflets form a pair on opposite sides of the leafstalk, while the third stands by itself at the tip of the leafstalk. Small greenish flowers grow in bunches attached to the main stem close to where each leaf joins it. Later in the season, clusters of poisonous, berrylike drupes form. They are whitish, with a waxy look.

Both poison oak and poison ivy - as well as poison sumac - contain a sap that is laced with resin. This resin (which resembles lacquer) comprises a number of different chemicals that produce a sensitizing reaction in most - but not all - people who touch them. Contact sufficient to cause a reaction does not have to be prolonged: It can consist of simply brushing against either leaves or bare stems.

Secondary contact is also possible and indeed may be even more common because people are not being alert to the possibility of exposure. For example, a person could contact poison oak by petting a dog who had rubbed up against a plant in the woods. Smoke is an especially effective method of secondary contact because smoke from burning poison oak plants can quite effectively spread resin across any uncovered body part and inside the body to the lungs.

Although initial contacts with poison oak tend to be fairly innocuous, later exposures can produce quite serious reactions after a person has become sensitized to the resin. In either mild or moderate cases, the initial contact does not produce any effects. These effects do not begin to show up for several hours as the skin that has been exposed first reddens and then begins to itch.

In most cases, the next stage is the appearance of small, water-filled blisters. This tends to coincide with the period of maximum itching. In the most severe cases, the blisters will be much larger and will tend to merge into each other. In even the most severe case, the rash recedes in between one and four weeks without any treatment - although most sufferers do use topical medications to reduce the itching. Reducing itching...

The sap is released when the plant is bruised, making it easier to contract Rhus-dermatitis in the spring and early summer when leaves are tender. The sap may be deposited on the skin by direct contact with the plant or by contact with contaminated objects, such as shoes, clothing, tools and animals. Severe cases have occurred from sap-coated soot in the smoke of burning plants. Because urushiol is inside the plant, brushing against an intact plant will not cause a reaction. But undamaged plants are rare because "Poison oak, ivy and sumac are very fragile plants," says William L. Epstein, M.D., professor of dermatology, University of California, San Francisco. Stems or leaves broken by the wind or animals, and even the tiny holes made by chewing insects, can release urushiol.
Having established the reasons why humans might want to remove poison oak from certain areas - for it has a right to be unmolested whenever possible, as do all species - we may now investigate the different possible eradication methods.

Controlled Burning

Although burning poison oak is an effective means of removing it, it is also potentially extremely dangerous, causing exposure to people far from the fire. The National Institutes of Health, among others, urges that poison oak not be burned as a method of control. In areas in which there is a great deal of poison oak, any area where there is to be a controlled burn should in fact be inspected to determine whether or not there is poison oak in the area.

Smoke from burning poison ivy and poison oak has poisoned people who were otherwise immune. Inhalation of such smoke results in lung poisoning that can require hospitalization and intensive care. The oil is not volatile at bonfire temperatures. Any transmission from smoke is by droplets on particles of dust and ash in the smoke, rather than from vapors.

Other methods are just as effective at removing poison oak without being potentially dangerous (viz Parkinson 2002). Burning is especially dangerous because it can affect people at a substantial distance: They may well not know that they have been exposed until they find themselves in respiratory difficulties.

Mechanical Control

There are a number of methods of effective mechanical control in removing poison oak. These vary in large measure due to where the plant is growing. For example, special techniques must be used in removing poison oak from trees:

Poison ivy and poison oak vines climbing on trees should be cut at the base, and as much of the vine as possible should be pulled away from the tree. Often, tree roots and poison ivy roots are so intertwined that grubbing is impossible without injuring the tree.

Not all mechanical methods of removal are equally effective, and not all of them will be effective during the first try. The roots of the plant are often quite tenacious as well as being relatively frangible, meaning that they are likely to break off and leave enough root material behind for the plant to regenerate.

Mowing with a scythe or sickle is not an efficient means of controlling poison ivy and poison oak. It has little effect on roots unless it is repeated frequently. Cutting plants and allowing the sap to be exposed can present considerable risk to those who might come into contact with it.

A single plowing is of little value in combating poison ivy and poison oak, but good seedbed preparation and planting cultivated crops for 1 or 2 years will control them.

Herbicides and Poison Oak

There are a number of herbicides that are effective at eradicating poison oak. As with any treatment of an area with herbicide, its overall toxicity and effects on other specices (both plant and animal) must be considered, as must potential contamination of water sources.

A wide number of herbicides can be effectively used against poison oak, with aerial application still quite popular, as it has been for decades. It must be noted again that aerial spraying does of course have its own risks associated with it.

Among the herbicides currently used are the following:

Glyphosate…