written 6/1/2024, updated 6/17/2024
Family Anacardiaceae
The Cashew/Sumac Family: Deciduous trees and shrubs that produce an oily or milky sap that can be highly poisonous. Resin canals that exist in stems, leaves, and roots are found in all plants in the family. Their fruits are called drupes (stone fruit) where the fleshy part of the fruit surrounds a single shell which houses a seed
Common Plants: Anacardium occidentale (Cashew); Mangifera indica (Mango); Pistacia vera (Pistachio); gen Cotinus (Smoke Tree); gen Rhus (Sumac); gen Toxicodendron (Lacquer Tree, Poison Ivy, Poison Oak, Poison Sumac)
Note: The Toxicodendron genus used to be lumped under Rhus. Toxico — dendron means toxic — tree.
Poison Ivy (Toxicodendron Radicans)
Native to most of the USA and southern Canada, it can be found in many types of environments from wet to dry, woodlands, valleys, clearings, roadsides, and backyards. Poison ivy can exist as either a shrub (trailing, erect, or bushy) or a woody climbing vine with aerial roots. It exhibits woody underground rhizomes. All aspects of the plant are poisonous, containing the persistent oily irritant, urushiol. It is said that the vine version can cause 10–100 worse symptoms than the shrub variety
Size: 6 ft shrub or 62–150 ft climbing vine
Location: Various areas from wet to dry, woodland to ditches to backyards
Uses: Food and shelter to animals, birds, and insects
Identification: Leaflets of 3 where the middle leaflet is longer than the other 2. Leaves can be smooth, serrated, or lobed. It has gray, reddish stems, and glossy green leaves that turn vibrant reddish yellow in autumn.
Flowers and Fruit: Flowers are many and clustered; Fruit look like waxy, greenish-white berries
Control: Do NOT burn. Fully cover the skin, protect face and eyes, wear a hat. Remove any gear and clothing that come into contact with the plant. Cut and remove roots of plant. Do NOT put in compost pile. Rather, place in trash bag. Use of herbicides on exposed roots/stumps.
Note how the middle leaf is set out longer than the other 2 leaves. This is characteristic of Poison Ivy
Here you can see the Poison Ivy interspersed amongst other plants and vines. The red are Poison Ivy, the purple is English Ivy, and the blue are Virginia Creeper
There’s a massive Poison Ivy problem at this house. Can you spot it amongst all the other plants here?
The vine variety
Poison Oak (Toxicodendron pubescens)
Low-growing shrub native to Central and Eastern USA, it is found in dry, sandy locations in woodlands and thickets. The word pubescens is latin for “covered in hair,” and the plant is named such owing to the fine hairs on stems and leaves. The plant roots are rhizomes and often form dense colonies. Yellowish-green flowers appear in the springtime, resulting in green-tannish white drupes (fruit) by late spring. All aspects of the plant are poisonous, containing the persistent oily irritant, urushiol.
Size: 2–4 ft shrub on average, can be as tall as 10ft
Location: Prefer dry, sunny areas. Woodlands, thickets.
Uses: Food and shelter to animals, birds, and insects
Identification: Alternating green, lobed leaflets of 3 that crowd towards the end of the stem. The leaves look similar to Oak tree leaves. Often, the middle leaf is fully lobed while the other 2 are irregularly lobed. Fine hairs cover the both the undersides and upper parts of leaves as well as the stems. Tend to grow in clumping colonies. Leaves turn vibrant reddish yellow in autumn.
Flowers and Fruit: Flowers are hanging yellow-green panicles (like rice or oats), and fruit are clusters of hairy green or tannish-white drupes that appear waxy
Control: Do NOT burn. Fully cover the skin, protect face and eyes, wear a hat. Remove any gear and clothing that come into contact with the plant. Cut and remove roots of plant. Do NOT put in compost pile. Rather, place in trash bag. Use of herbicides on exposed roots/stumps.
SOURCE. You can see how they grow in clumps. Notice how the 2 leaves are more irregularly lobed than the middle leaf which, like poison ivy is set out a little
Poison Sumac (Toxicodendron vernix)
Deciduous small tree or shrub, it is native to eastern and central-eastern USA, and eastern Canada. There are many look-alike plants. Typically, Poison Sumac will not grow in clumps and since it prefers wet areas, will not be found in dry locations, nor will it be commonly found along roadsides and fields. While it is the least likely of the big 3 to be exposed to, effects of the urushiol from Poison Sumac tend to be more severe than its Poison Oak and Ivy relatives.
Size: 5–25 ft tree with sparse, open form, or erect shrub
Location: Prefer marshy, boggy, wet locations like riverside thickets, acidic soil, and full to part sun
Uses: Food and shelter to animals, birds, and insects
Identification: Long, smooth, paired leaflets of 7–13, with a single leaflet at the end. Stems are reddish, bark is smooth, gray-brown in color, and contain lenticels (small holes or lines on trunks that facilitate gas exchange). Leaves turn reddish yellow in the autumn. Black sap
Flowers and Fruit: Greenish-yellow, 5‑petal flowers hanging in panicles (think rice and oats). Fruits are yellowish-white drupes that hang loosely downwards in clusters
Control: Do NOT burn. Fully cover the skin, protect face and eyes, wear a hat. Remove any gear and clothing that come into contact with the plant. Cut and remove roots of plant. Do NOT put in compost pile. Rather, place in trash bag. Use of herbicides on exposed roots/stumps.
Reddish stem, leaflets ending in a single leaflet, grayish brown bark
Urushiol
Urushiol is an oleoresin (oil + resin) found in the sap of plants in the family Anacardiaceae. It has potent allergenic properties that affect most humans on contact, causing urushiol-induced contact dermatitis. The chemical is persistent and can last for months on clothing and gear unless cleaned thoroughly with soap + water or rubbing alcohol.
Its irritating effects are only applicable to humans and a few primates. Other animals like dogs, cats, deer, birds, etc. are not affected. In fact, birds, deer, cattle, goats, and other wildlife benefit and feed from the plants.
Sciency Stuff
Toxicohedron Control — Before and After
Vinegar Solution
Pros: Natural ingredients, no harsh chemicals
Cons: Strong vinegar smell, easily washed off with water/rain, must use strong enough vinegar concentration, for best results use when sunny and hot, not substantive and needs reapplication
Regular white vinegar is only 5% acetic acid (and 95% water). You’re definitely going to want a higher concentration for this which can be found easily in hardware stores up to 30% (usually in the cleaning and/or garden sections), but you can get them even higher online. I ended up buying the 45% concentrated solution (there’s even 75% or 95%). The general formula is:
1 gallon Vinegar (read the label on the concentrated ones for dilution ratio)
1 Tbsp Dishsoap
1 cup Salt
Get yourself a nice pump sprayer like the one I use (can be any brand, I just happened to have this)
You can also buy pre-mixed weed killer solutions like this one that I tried for regular weeds. Notice that it’s 20% vinegar which I found to be good for most weeds, but not enough for some tougher ones like crab grass.
Results of Vinegar
1 week apart
2nd treatment
3rd treatment
RoundUp and similar products
Pros: Strong, substantive, 30-minute rain ready
Cons: Environmental persistence and downstream effects, possible health implications
I really dislike using RoundUp, but I really don’t want to mess with Poison Ivy especially given my terrible reaction to it. Ever since the issue with glycophosphates and cancer, RoundUp has changed their formulations away from glycophosphates. Also, RoundUp doesn’t care if it rains (30 minute rain ready) or if it’s sunny outside. It’s likely more substantive than vinegar, too. Just make sure you use eye protection and a mask
Active ingredients:
Triclopyr, triethylamine salt (0.122%) — selective herbicide for broadleaf and woody plants
Fluazifop-P-butyl (0.097%) — selective post-emergent herbicide
Diquat dibromide (0.073%) — non-selective algicide defoliant, dessicant, and herbicide
I chose the RoundUp specifically for poison ivy. The built-in wand is rather subpar. If you have one, it’s better to dump it into a pump sprayer and do it that way
Results of RoundUp
Before
After
I drenched the holy heck out of this plant with the RoundUp. It did not work as well as I thought it would
Fun Facts
The name urushiol comes from the Japanese name for the lacquer tree, urushi.
In 2016 an international group of scientists discovered that a molecule found abundantly in human skin, CD1a, is responsible for the reaction of humans to urushiol contact. CD1a is expressed by Langerhans cells in the skin. Langerhans cells are part of the immune system, and the CD1a molecule it produces acts by presenting lipid antigens to T‑cells. Since urushiol is an oleoresin, the now activated T‑cell releases cytokines, causing both inflammation and itchiness. Interleukin-33 was isolated as a key cytokine in mouse studies, along with its receptor ST2 on the small to medium dorsal root ganglion neurons. By blocking the interleukin-33/ST2 (IL-33/ST2) signaling pathway, relief from the horrible itchiness of urushiol can be attained. Interestingly, IL-33 is also associated with eczema/atopic dermatitis and asthma. With this information, a vaccine is currently in the works to help desensitize the body to urushiol’s potent irritating effects.
Urushiol is found in some members of the Anacardiaceae family including poison ivy, oak, and sumac, as well as mango skins, cashews, and pistachios
