Sunday, April 11, 2010

Don't Touch

Poison Ivy ( Toxicodendron radicans )

Growing as either a groundcover or a vine self attaching to trees by means of aerial roots and reaching up to 100 feet into the canopies of trees. Trunk diameters up to 7.7 inches are known.
Poison Ivy is one of the most noxious weeds on the continent and over 70 % of the human population is at least somewhat allergic to it breaking out in rashes which can be severe. It is however a valuable food for wildlife and many birds do eat the whitish-gray berries that appear in the fall and winter. Poison Ivy can be an attractive foliage plant with its scarlet fall color but should NEVER be used in the landscape. It should also NEVER be introduced into Europe where it has serious potential as an invasive exotic weed. A similar equally poisonous relative grows in temperate regions of eastern Asia and Poison Oak is a variant with deeper lobed leaflets that is more commonly found in the west.
Touching any part of the Poison Ivy plant can cause dermatitis, often severe in the majority of people that are allergic to urushiol, a chemical compound contained in this plant. Urushiol causes redness, itching and water blisters in people sensitive to this compound ( which is about 70% ). Often a first time exposure to this plant has no effect but will sensitive people to future exposures which often result in severe reactions. Within a few hours to a few days, the bodys immune system will attack the affected skin as if it were a foreign invader and not part of the body.
The sap of Poison Ivy, even dried resins during the winter, is always toxic however slightly more potent during late spring.
Cortisone is sometimes prescribed for severe Poison Ivy infections however Cortisone itself may have severe side effects including severe swelling and less resistance to secondary infections such as Staph.
Homeopathic preparations made of Rhus toxicodendron ( not the botanically correct name but it most certainly is Poison Ivy ) is reported to make people immune to Poison Ivy. Due to my severe allergies to this plant and a secondary Staph infection I will be trying this remedy for this workplace hazard and reporting on its success.
While an employee at a local natural health specialty store backs up this claim I can find little online. In theory a mini exposure with the homeopathic grade material would work in the same way as the flu shot desensitizing people from the real thing.
I would suspect one would need a very small exposure every day for a period of 3 to 4 weeks during each spring to accomplish at least partial immunity. I will not fully endorse this product until I see extensive studies on its effectiveness.
More info on Rhus toxicodendron homeopathy ( ).
People that are likely to get exposed to Poison Ivy should take daily Allicin Garlic Pills which makes the blood a less hospitable for secondary infections if you do get exposed. ALL landscapers and people that work outdoors should take Poison Ivy very seriously. It is not a joke, many people require hospital treatment for this plant and for people with poor circulation and diabetes, Poison Ivy infections can even cause loss of limb. If you do get exposed to urushiol, wash it off with specialized Poison Ivy soap as soon as possible since it binds to the skin within very short time. Removing the resin as quickly as possible will lessen the severity of the infection. Despite being a severe allergen to most humans, Poison Ivy is food to wildlife. Bees use the flower nectar, many birds eat the berries ( propagating the plant as they drop the seeds ), goats and deer eat the foliage.
Growing in sun or shade, and hardy from zones 3 to 10; Poison Ivy is one of the most widespread of all plants on the North American continent.
Cultivating Poison Ivy is not recommended though I have seen it used on fences to keep out intruders ( however your neighbors may not welcome you in the neighborhood ). It is easy to propagate from seed or cuttings. Poison Ivy is considered a noxious weed in many U.S. states and Ontario, Canada to as far north as Tobermory and Haliburton ( the non-climbing subspecies rydbergii is found much further north to Kenora to Sioux Lookout to Lake Nipigon to Pagwa to Ranoke in Ontario ).
To control large vines should be cut with the fresh cut treated heavily with a high concentration of Roundup repeatedly over the first few hours. Groundcover and Poison Ivy plants with reachable foliage should be treated with Roundup either once or preferrable twice over the same day then left until the roots die and the entire plant collapses. Do not spray when there is wind because the spray will kill any desirable plants that it hits.
NEVER burn Poison Ivy since breathing the smoke can be extremely dangerous. The smoke can swell the lungs and be deadly.

Link to article on Wikipedia

* photos taken on April 11 2010 @ U.S. National Arboretum, D.C.

* photos taken on April 22 2010 in Howard County, MD

* photos taken on June 15 2011 in Columbia, MD

* photo of unknown internet source

* photos taken on Oct 8 2011 in Odenton, MD

* photo taken on Apr 15 2014 in Columbia, MD

* photos taken on Apr 22 2015 in Ellicott City, MD

* photos taken on Apr 24 2015 in Clarksville, MD

* historical archive photo

* photo taken on May 30 2015 in Columbia, MD

Toxicodendron ambigua ( Chinese Poison Ivy )
Also called Toxicodendron orientale. A huge extremely invasive vine native to Sakhalin, China and Japan, that is nearly identical to Rhus radicans. It MUST NEVER BE PLANTED IN NORTH AMERICA!!!
The leaves are often larger than Toxidodendron radicans, sometimes up to 20 inches across. The leaflets average 6 x 4 inches in size but can be larger.

Toxicodendron diversilobum ( Oakleaf Poison Ivy )
Also called Poison Oak. It is similar to Poison Ivy but more common in the west with leaves that are much deeper lobed.

Toxicodendron succedaneum ( Wax Tree )
Also called Rhus succedanea. A spreading small deciduous tree native to eastern Asia. Some records include: 20 years - 33 x 27 feet; largest on record - 60 x 33 feet.
The pinnate leaves, up to 12 inches in length, are composed of 9 to 15 pointed oval leaflets, up to 7 inches in length. The foliage is glossy green, turning intense scarlet-red and orange in autumn. The autumn color is intense even in warm climates. This tree is highly poisonous and if sap gets on the skin it can cause a painful rash.
The very small, light yellow flowers, borne in panicles, up to 5 inches,
They are followed by yellowish-brown berries borne in pendulous clusters.
Hardy zones 5 to 10

Rhus sylvestris
largest on record - 57 feet with a trunk diameter of 20 inches

Toxicodendron verniciflua ( Varnish Tree )
Also called Rhus verniciflua
eastern Asia's ( China and Japan ) counterpart to the Poison Sumac, it grows larger to around 60 feet in height. Some records include: fastest recorded growth rate - 2 feet; 20 years - 30 feet; largest on record - 100 x 50 feet with a trunk diameter of 3 feet; largest in England - 70 feet.
The pinnate leaves, up to 32 inches in length, are composed of up to 7 to 13 pointed oval leaflets, up to 8 inches in length. The foliage is bright green, turning to scarlet-red in autumn.
The small creamy-yellow flowers, borne in pendulous loose panicles, up to 8 inches in length, during summer.
They are followed by pale-yellow rounded berries.
Hardy zones 5 to 9. Lime tolerant.

* historic archive photo

Toxicodendron vernix ( Poison Sumac )
Also called Rhus vernix. A fast growing, large shrub or small tree that is native to swamp forests in eastern North America ( from southeast Minnesota to central Michigan to Grand Bend, Ontario to Ottawa, Ontario to southeast Quebec to southern Maine; south to eastern Texas to northern is also found around the eastern end of Georgian Bay and Barrie, Ontario ). In the Windsor/Essex County, Ontario region; it was abundant in swampy areas from Colchester to Kingsville, around Point Pelee as well as on the Lake Erie islands during the 1800s. Some records include: largest on record - 33 x 30 with a trunk diameter of 1.5 feet. Short-lived, 75 years is considered the maximum life expectancy.
The pinnate leaves, up to 2 feet in length, are composed of up to 13 smooth-margined, pointed-oval leaflets, up to 5 x 2 inches. The foliage is glossy bright green, turning to scarlet-red during autumn. The leaves are crowded at the ends of the branches.
The greenish-yellow flowers, borne in panicles, up to inches,
They are followed by ivory-white berries, up to 0.6 inches, that are borne on clusters during autumn and often persisting through winter.
The ridged and warty twigs are gray-brown. The stems exude milky sap when broken.
The light gray bark is smooth other than the lenticels.
Hardy north to zone 4
Pharmacology: the sap and resins are poisonous and have the same ill effect as Poison Ivy though more intense.

* photo taken on April 11 2010 @ U.S. National Arboretum

* photo taken on June 18 2012 in Columbia, MD
* photos taken on Aug 27 2015 in Columbia, MD

* photos taken on Oct 19 2015 in Howard Co., MD

* photo taken on July 8 2016 in Columbia, MD

* photo taken on Jul 18 2017 @ Dominion Arboretum, Ottawa, ON

* historical archive photos


  1. Thanks for this picture. I can not tell you how hard it has been to get a decent picture of this on the web to know exactly what it is I am looking for - to not touch it!

  2. I'll be posting a full article later this year as I capture it in photos throughout the year.
    Many people do not know what Poison Ivy looks like. I have heard many "now I know what the itching was all about" after finding it growing in groundcover, on fences, tree trunks and even on peoples house exteriors. Often pets will get the sap on their fur and bring it in the house.
    For treatment I recommend waiting until it is in full leaf and blast the plant with Roundup. Let it soak in then an hour soak the plant again. With vining plants; the stems can be cut in winter and the spring regrowth soaked with the Roundup to kill the roots. Be vigilant since the white berries in the fall WILL sprout in the spring. Easier to get them when they are tiny since Poison Ivy can run underground once established.
    I hope its Asian relative never does get introduced to North America - it can be very invasive and is equally poisonous