Poison Oak

Poison Oak Information/Identification


Toxicodendron Diversilobum, commonly known as Poison Oak, is a woody vine or shrub in the Anacardiaceae family. The Anacardiaceae, often referred to as the cashew or sumac family are a family of flowering plants. Toxicodendron Diversilobum, found in California, produces an oil which causes itching, irritation, and allergic rashes in many humans after contact by touch. The leaves of Poison Oak consist of three leaflets, the central leaf always larger than the others. During each season the leaves change color or become leafless. Their leaves resemble those of a true oak but have a glossier leaf surface.


How it looks in different seasons

During the first few months of the year, when the leaves unfold, they are typically bronze and evolve to a bright green color when springtime comes. In summer, the leaf becomes yellow-green and slowly develops into the bright red from late July to October. Without leaves the stems may sometimes be identified by occasional black marks where its milky sap may have oozed. It often has scalloped, toothed, or lobed edges.

How it grows

The process of poison oak growth is simple. The vine form can climb up large shrubs or tree trunks, vertically rather than spiraling up the tree. Traveling vertically is actually healthy for the tree and does not damage the bark. When the vine moves up the tree, seeds and rhizomes (a continuously growing horizontal underground stem that puts out lateral shoots and adventitious roots at intervals) are created. It reproduces by spreading seeds and/or rhizomes.

Where it grows

Toxicodendron Diversilobum grows in a variety of habitats, like other plants in the Anacardiaceae family, such as riparian zones. Theses could include woodland, forests, and grassy hillsides. Poison Oak grows in the Pacific Region, and is specifically widespread in California. It thrives in shady areas through full and direct sunlight conditions.


Where is it native

Poison Oak is native to western North America with a distribution extending from British Columbia to Baja California peninsula. It is also native in the western regions of Washington state and Oregon. It is widely spread throughout Northern California.


Environmental / Human Needs

Why Poison Oak is good
While many humans lament its very existence, Poison Oak has numerous benefits for the species in its natural environment. Poison Oak can provide benefit to animals in two different ways: shelter and food. After rainfall causes rivers to flood or overflow, Western Pond Turtles can seek refuge in Poison Oak patches. Fox squirrels can take shelter inside Poison Oak bushes in the summer and eat the berries that it produces. The berries of the Poison Oak are a source of food for many birds, including quail, turkeys, woodpeckers, corvids, chickadees, bushtits, waxwings, thrushes, mockingbirds, thrashers, wrentits, warblers, sparrows, towhees, juncos, and finches (Baynature.org). The berries aren’t even the only nutritional part of Poison Oak plants; its leaves and stems are a source of food for herbivores such as deer, wood rats and pocket mice (Baynature.org). Poison Oak can also be beneficial for insects; bees can gather nectar from Poison Oak plants, and the leaves can provide shelter and food for moth larvae.

Why humans react to it

The agent that causes a negative reaction to Poison Oak is called urushiol, and is contained within the resin canals of Poison Oak plants. The itchy rash that follows exposure is the result of one’s immune system rejecting urushiol as a foreign agent.and producing antibodies at the site of contact. This condition is referred to as “contact dermatitis” by the medical community. The allergic reaction to urushiol can occur anywhere from several hours to several days after the initial exposure. In addition to primary exposure (direct contact with the plant), allergic reactions can occur as a result of secondary exposure, such as touching a glove or gardening tool that came into contact with Poison Oak. Yet another method of potential exposure can occur when piles of brush containing Poison Oak are burned; the resulting smoke may contain urushiol which can not only affect the skin, but also nasal passages, the throat, and lungs if inhaled.

Due to how undesirable it is to suffer through contact dermatitis, it is highly recommended that anyone who finds themselves spending time in the woods of the Pacific West takes precautionary, preventative steps toward avoiding exposure to Poison Oak. The first step that one can take is to be able to identify the Poison Oak plant. Familiarizing oneself with what Poison Oak looks like is the most important step toward avoiding it, as one would be able to identify it in the wild and change one’s course if necessary. However, even those who are able to flawlessly identify Poison Oak can fall victim to exposure from this sneaky plant. That is why the second preventative step is to cover one’s whole body with clothing or other protective equipment (such as gloves) when in areas of potential exposure. Furthermore, if it is suspected that one’s clothing has had contact with Poison Oak, it is advised to wash the clothes at one’s earliest convenience (while wearing gloves, if possible, as touching the clothes after exposure could lead to secondary exposure).

If Poison Oak is located in the area near one’s home, or in areas which are frequently visited, removal and proper disposal of the plant will prevent future exposures. Proper removal is discussed further down this page.


Path system / How we can live with it

With all of this talk about how bad an allergic reaction to Poison Oak can be, it would be easy for one to wish that this pesky plant would be eradicated. However, this is a rather human-centered perspective to take. It is crucial to remember that Homo Sapiens are just one of the many, many, many species that share the planet Earth, and it is important to consider how our actions may affect those other species. As mentioned earlier, not only is Poison Oak a plant worthy of respect in its own right, but it provides shelter and food to many animal species. Instead of hoping to eradicate it entirely, what should be done is making an effort to integrate our community and the natural habitat in a way that works for both.

While we should not remove Poison Oak from the entire forest, it is both acceptable and sensible to remove it from established walking paths, and from the margins around those paths. The widely accepted margin is to remove Poison Oak from 4 feet of either side of a walking path. If a Poison Oak plant is left within that margin, it may (and probably will) creep onto the path itself and make contact with innocent nature enthusiasts. When removing Poison Oak, proper protocol should be followed. It is imperative to not just pluck the section of the plant that juts above ground level, but to pull the root from under the ground. Otherwise, the root will simply grow back another stem in the exact same place as the one that was plucked. Poison Oak is a resilient plant, thus one must be persistent when trying to remove it from an area; it is advised to continually revisit an area and remove any new roots that may have made their way into.
There are procedures and protocols to follow when removing Poison Oak so as to absolutely minimize the risk of exposure. The first, as previously mentioned, is to ensure that all of one’s skin is covered with clothing or protective gear; protective gloves are an absolute necessity. The second protocol is to have a disposable sheet to put removed plants onto. Second-hand stores tend to be a good source of inexpensive sheets. After the sheet has been filled up, or removal is complete, it is proper etiquette to tie it up (while still wearing gloves!) and throw it away. Finally, put all clothing into the laundry, including gloves. It would be a shame to follow all proper procedure avoiding primary contact, and then fall victim to secondary contact as a result of one’s clothing having urushiol on it.

Poison Oak Removal

Removal Techniques


Although there are many benefits to the poison-oak population, its effect on humans drives our need to remove it from our immediate surroundings. Throughout the internet you can find both mechanical and chemical tips for removing the poison oak plant. This article will focus on mechanical control and removal of poison-oak in order to avoid any harmful chemicals being introduced to people, pets, or healthy wildlife. It is best to repeat these removal techniques over a period of a few years in order to ensure that the removal is effective and permanent.


Being thorough is crucial when removing poison oak; stems and rootstocks will quickly resprout if the entire plant is not eliminated. Powered tools, such as bush rakes, lawn mowers, and bulldozers leave much of the plant and can actually be counterproductive to removal if the brush is spread throughout the area.  The most effective technique for mechanically removing poison-oak is by hand pulling and grubbing via shovel or pitchfork.  Grubbing is defined as digging superficially, or shallowly, in the soil. It is essential here to be careful and meticulous; make sure you are following the full rootstock without breaking off any pieces that may grow back. The best time of year to perform eradication is in early spring or late fall because the soil is moist and easier to dislodge full rootstocks.  


As mentioned previously, there are benefits to poison oak, specifically the food source it provides to migrating birds, and it is possible to coexist with this plant. Poison oak is a rather intelligent plant; if it is cut and physically pulled back from a walking path, it will eventually stop using its resources to grow where it is continuously removed. Being a vine, it prefers to grow up trees and once the large vine is cut from a tree, you will begin to notice a widespread sprouting of the plant. If possible, allowing it to live against the tree, and maintaining a healthy cover of desirable vegetation will actually reduce the potential for a widespread invasion.


Goats and sheep can be effective in removal of poison-oak in small areas. The difficulty with this technique is that they are harder to come by and may eat all other vegetation as well.


One thing to remember is that poison-oak is a native and natural component of the Western United States plant community, so biological removal is ineffective and not recommended.


Disposal Of Poison Oak


The MOST important thing about disposing poison-oak is that you MUST NEVER BURN IT.

The smoke will contain urushiol and resin from the plant and can create lethal inflammation in the nasal passages, throat, and lungs.


Detached and dried brush oak and plant material can cause reactions so it must be buried or stored out of harm’s way. Plant oils can remain in materials and on surfaces for a long time and these items must be properly washed out or disposed of. We recommend using a sheet to load and dispose of the plant materials because they can be thrown out and will decompose with the plant. Tarps are also effective but must be thoroughly washed before subsequent use because later contact can cause painful and itchy dermatitis.  


It is recommended to check with your town or county’s policies on removal and disposal of plant materials such as poison oak and poison ivy. For example, Santa Cruz County Public Works does not allow poison-oak in their Woodwaste and Yardwaste Drop-Off, but the Santa Cruz County Greenwaste service will accept it. If you have the space on your land, it is helpful to bury or stack the material in an out-of-the-way location.


Safety First


When it comes to mechanically removing poison oak, keeping yourself safe needs to be your FIRST priority.


You need to cover yourself from head to toe to avoid irritation caused by urushiol; we call this process gowning and gloving.


Clothing Items should include:

  • Long Sleeves *Multiple layers is best
  • Long Pants *Multiple layers is best
  • Socks
  • Boots
  • Jackets
  • Thick rubber gloves
  • Washable cotton gloves over the top of rubber gloves
  • Safety glasses


As stated before, urushiol stays on the skin, clothing, shoes, and tools, for a long time if not properly removed.


Treatment Following Exposure


As soon as you come in contact with poison-oak you should wash AS SOON AS POSSIBLE.



  • Use soap and water to vigorously scrub the skin as soon as possible after contact.
  • When thoroughly washing one’s hands, it is advised to pay extra attention to the space underneath one’s fingernails
  • A helpful and effective product following exposure is Tecnu, which is an outdoor skin cleanser specifically manufactured to remove the hazardous oils that come from poison oak, ivy, and sumac plants. It can also be used to wash clothes and pets when necessary.
  • The mechanical motion of scrubbing is the most important part of washing off the urushiol. A helpful tip is to act as though you are scrubbing off grease from an automotive shop.


Clothing and other materials:

  • Wash clothes and other cloth materials on a hot water cycle as soon as possible from the time of exposure.
  • Tools and shoes should be hosed down strongly or cleansed with alcohol to avoid further contamination.


Longer-Term Treatment

When the rash appears (which can occur as soon as several hours after exposure or as late as several days after), it will be very tempting to itch it. However, it is advised to abstain from itching, as continual itching can lead to infection, further prolonging the rash (Healthline.com). Most drug stores carry products that will alleviate some of the itching after the rash has appeared, such as hydrocortisone cream or calamine lotion.
As every body’s immune system differs, some people may be extra sensitive to urushiol, prompting a dangerous reaction that may require immediate medical attention. Proper medical attention should be sought if any of the following symptoms occur: difficulty breathing or swallowing, swelling of the eyes or lips, a rash that covers more than 25% of one’s body, a rash on one’s face, swollen lymph nodes, headache, nausea, and/or fever (Healthline.com). One should also seek medical attention if a rash lasts more than 10 days, or if the rash appears to be infected (blisters are producing pus, yellow liquid, or an odor).




“Poison Oak” Statewide Integrated Pest Management System


“Poison Oak Has a Good Side, Too” Bay Nature



“Leaves Of Three- The Rash Success of Poison Oak” Bay Nature


“Allergies to Poison Ivy, Oak, and Sumac” WebMD


“Poison Oak Rash: Pictures & Remedies” Healthline
http://www.healthline.com/health/outdoor-health/poison-oak-pictures-remedies# Remedies5


  1. M. DiTomaso and W.T. Lanini. Pest Notes: Poison Oak. UCANR Publication 7431. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7431.html


Hauser, S. C. 1996. Nature’s Revenge: The Secrets of Poison Ivy, Poison Oak, and Poison Sumac, and their Remedies. N.Y.: Lyons & Burford


  1. DiTomaso. Removing Poison Oak From Landscapes and Recreational Areas. UC IPM Green Bulletin August 2013 edition. May 24, 2014. Accessed Feb 3 2017. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13858


L.J. Vorvick, MD. Poison Oak, Ivy, Sumac Rash. MedlinePlus. School of Medicine, University of Washington, Seattle, WA. Aug 14, 2015. Accessed Feb 3, 2017. https://medlineplus.gov/ency/article/000027.htm


Shofner JD, Kimball AB. Plant-induced dermatitis. In: Auerbach PS, ed. Wilderness Medicine.6th ed. Philadelphia, PA: Elsevier Mosby; 2012:chap 63.


Santa Cruz County Residential Recycle Guide.Greenwaste. Jul 2011. Accessed Feb 3, 2017.



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