western poison ivy

Specially Regulated Plant

In 2010, the Minnesota Department of Agriculture added eastern poison ivy and western poison ivy to the Specially Regulated Plant list.

Must be eradicated or controlled for public safety along rights-of-ways, trails, public accesses, business properties open to the public or on parts of lands where public access for business or commerce is granted. Must also be eradicated or controlled along property borders when requested by adjoining landowners.

Poison ivy is beneficial to many wildlife species, but exposure to it causes severe skin irritation to humans and sometimes to livestock. Smoke from burning it can cause serious respiratory problems.

Great Plains

FACU - Facultative upland

Midwest

FAC - Facultative

Northcentral & Northeast

FAC - Facultative

Western poison ivy is an erect, perennial shrub that rises on a single stem from a usually underground rhizome. It often forms colonies. The plant is usually a ground cover, sometimes a shrub, rarely a vine. If it is a vine it climbs weakly, and will not climb trees.

Stems are woody, erect, usually unbranched, and lack aerial roots.

Leaves are alternate and are borne near the end of the stem usually on leaf stalks. The leaf stalks are hairless and ½″ to 10″ long. The base of the leaf stem is enlarged and grooved. When the leaf is absent, a u-shaped or v-shaped scar remains.

The leaves are divided into 3 leaflets. The leaflets may be egg-shaped, with the broad portion at the base where it attaches to the leaf stalk, or diamond shaped, broadest in the middle and tapering toward both ends. They taper to a point at the tip. They are 1″ to 6″ long. The two side leaflets are usually shorter than the central leaflet. The leaflet margins may have shallow lobes, they may have rounded teeth, or they may be entire. They tend to be folded slightly along the midrib, not flat. The upper surface is usually entirely hairless, or there may be a line of curly hairs on the midvein. The lower surface is either entirely hairless or has appressed hairs. In the spring the leaves are glossy and have a reddish tint. Throughout the year young leaves are shiny becoming dull with maturity. In the fall the leaves turn yellow to orange, rarely bronze to red.

Black spots may appear on any part of the plant. The spots are urushiol, the resin that causes allergic reactions. When the plant is damaged urushiol is exuded in an attempt to seal off the damaged area. The resin is creamy, turning brown-red then black with oxidation.

The inflorescence is an elongated, 4″ to 16″ long, unbranched or sparingly branched cluster with usually fewer than 25 flowers. The flower has 5 yellowish petals.

The fruit is a hairless, greenish-white, berry-like pome that turns ivory at maturity. It is distinctly ridged, “like a pumpkin”. The fruit cluster is compact and erect.

Up to 60′ long

Yellowish

Boxelder (Acer negundo) saplings may have 3 (usually), 5 (occasionally), or 7 (rarely) leaflets. When it has 3 leaflets it can be indistinguishable from western poison ivy.

Eastern poison ivy (Toxicodendron radicans ssp. negundo) is a vine, not a shrub. It climbs trees. The stems have aerial roots. The leaf stalks are densely hairy. The leaflets tend to be flat, not folded along the midrib. The inflorescence is 3″ to 4″ long. The fruit cluster hangs downward.

Dry to moist. Wood edges, prairies, fences, beneath utility wires. Full shade to partial sun.

June to August

The sap of this plant contains the allergenic urushiol. Urushiol is not a single chemical but a complex of five chemicals called alkylcatechols.

Several exposures to the substance may be necessary to impart sensitivity. Research has shown that 85% of all people will develop contact dermatitis after adequate exposure. It usually takes 12 to 48 hours for a rash to develop on a previously sensitized person. In some individuals, a single exposure will cause a reaction. In these individuals, the rash will develop in seven to ten days.

The lesions last 14 to 20 days. Rashes do not spread and are not contagious. Treatment can dry the blisters, reduce swelling, and relieve itching, but will not speed healing.

Contact with the outer surface on an undamaged plant should not cause an allergic reaction unless there is residual urushiol present from a previous injury to the plant or a nearby plant. Contact with a torn leaf, broken or damaged stem or rhizome, or black spot will cause a reaction in those sensitized to urushiol.

Sources

2, 3, 4, 5, 7, 8, 22, 24, 28, 29, 30.

Native

Common and widespread

Poison Ivy...

With abundant rains etc. vegetation including poison ivy is flourishing in some areas. At Frenchman’s Bluff SNA is no exception. I took this photo because the plants weren’t all in big masses like some areas. Just to show the leaves of three better. Also sighted was a red and black Poison Ivy Sawfly. Interesting creature that looked almost other world like from some angles. The larvae of that species feeds on poison ivy which is a good thing as there is plenty of it in areas out there.

Poison Ivy....

I wasn’t sure just what it was but I knelt down to tie a shoe and my knee must have been on some and I got a itchy rash on it. I just washed my knee area and put some stuff for itch on it and it eventually went away. Had also noticed a few small red spots on my ankles that itched. Guessing the same thing. I looked it up and it appears to be poison ivy. It was at Frenchman’s Bluff SNA and seems to be in several different areas throughout that SNA. I have encountered other areas in some woodlands even certain weeds can cause itching. I have actually become immune to some types. The poison ivy irritation didn’t last that long and didn’t spread to any place else thankfully. But probably differs with each individual. I’ll be more careful where I kneel down to tie a shoe when out and about in certain areas.

Colony

Plant

Inflorescence

Leaves

Black Spots (Urushiol)

Aboveground Rhizome

Location: Frenchman’s Bluff SNA

With abundant rains etc. vegetation including poison ivy is flourishing in some areas. At Frenchman’s Bluff SNA is no exception. I took this photo because the plants weren’t all in big masses like some areas. Just to show the leaves of three better. Also sighted was a red and black Poison Ivy Sawfly. Interesting creature that looked almost other world like from some angles. The larvae of that species feeds on poison ivy which is a good thing as there is plenty of it in areas out there.

Luciearl
2/20/2024

Location: Fairview Twp, Cass County

Luciearl
1/31/2024

Location: Fairview Twp, Cass County

Location: Kellogg Weaver Dunes SNA, Weaver Dunes Unit

Blooming Poison Ivy

Location: Frenchman’s Bluff SNA

I wasn’t sure just what it was but I knelt down to tie a shoe and my knee must have been on some and I got a itchy rash on it. I just washed my knee area and put some stuff for itch on it and it eventually went away. Had also noticed a few small red spots on my ankles that itched. Guessing the same thing. I looked it up and it appears to be poison ivy. It was at Frenchman’s Bluff SNA and seems to be in several different areas throughout that SNA. I have encountered other areas in some woodlands even certain weeds can cause itching. I have actually become immune to some types. The poison ivy irritation didn’t last that long and didn’t spread to any place else thankfully. But probably differs with each individual. I’ll be more careful where I kneel down to tie a shoe when out and about in certain areas.

Location: McCarthy Beach State Park

Location: McCarthy Beach State Park

Location: Pennington Co MN

Location: Pennington Co MN