Alan -
I guess the best way to start out is that your best defense is with good, reliable, substantiated information. That old adage of "leaves of three, leave the be" is too broad and over the many years has encouraged people to be afraid of more than just the toxic trio (poison ivy, poison oak, poison sumac). Sorry, much as I respect "old timers" knowledge on a number of subjects this is an area where I just have to disagree. There is good credible science behind the statements I make here.
First off, lets go into the more common species of Toxicodendron (Rhus has not been used in several decades) and where you can find them. There are 2 species of poison ivy - toxicodendron radicans and toxicodendron rydbergii. The first is the vine / climber that many of us are familiar with and is called eastern poison ivy. This is the most widespread of these Toxicodendron species I'll be discussin here. You can find the distribution map here: USDA information on poison ivy. Toxicodendron rydbergii is generally a shrub called western poison ivy and found in a smaller area of the country. The distribution map is here: USDA information on western poison ivy.
There are 2 species of poison oak - toxicodendron diversilobum and toxicodendron pubescens. Toxicodendron diversilobum or pacific poison oak is found only in the western-most states and may grow as a shrub or wood vine. The distribution map is here: USDA information on pacific poison oak. Toxicodendron pubescens or atlantic poison oak is found in midwest, southern and eastern states. The distribution map can be found here: USDA information on atlantic poison oak. Toxicodendron pubescens used to be called toxicodendron toxicarium but the scientific name was changed in recent years to better describe the plant (yes the name does mean something). Atlantic poison oak is not common as the distribution maps would imply. Atlantic poison oak grows as a shrub not a vine. It is in your area of the country but note that it is a shrub not a vine.
Toxicodendron vernix is called poison sumac and can be found in swampy areas in the eastern states including Tennessee. The reason most people do not come across the plant is due to its desired habitat - swamps, bogs, constantly moist areas. Here is a distribution map for poison sumac: USDA information on poison sumac.
Now for plant identification. I'll start with poison sumac as it is the standout. Poison sumac grows as a small deciduous shrub with alternating compound leaves with 7 to 13 leaflets. The leaflets are short-stalked, elliptic or egg-shaped, broadly pointed at base, pointed at tip, margin untoothed, lustrous above, paler beneath. The berries on this plant are white in color, hence the adage "berries of white, take flight". The only other sumac I am aware of which is similar (untoothed margin on the leaves) is smooth sumac and the location of the flowers and fruit, and fruit color are a means to determine which plant smooth sumac or poison sumac you are looking at. Smooth sumac berries are red.
Since toxicodendron diversilobum (pacific poison oak) is nowhere near you, I'll stick to just identifying toxicodendron pubescens. I prefer to use "The Illustrated Book of Wildflowers and Shrubs" by noted botantist William Carey Grimm as a foundation for plant identification. From this book, we find that atlantic poison oak is a sparingly branched, deciduous shrub 1 to 2.5 feet high; growing in dry sandy pine and oak woods and clearings. The compound leaves are alternate and long stalked with 3 leaflets. The leaflets are often egg-shaped, pointed at base, blunt at tip, with 3 to 7 deep lobes resembling an oak leaf. The leaflets are downy above, more so and paler beneath. The end leaflet is long-stalked (like poison ivy) and the side leaflets are almost stalkless. Again, the fruit is white just as with poison sumac and poison ivy.
Now we're down to poison ivy - toxicodendron radicans and toxicodendron rydbergii. According to the distribution maps, toxicodendron rydbergii is not in Tennessee so we'll stick to the more common, toxicodendron radicans. Poison ivy is a small trailing deciduous shrub or woody vine climbing by means of aerial rootlets on the stems; growing in wooded areas, thickets, clearings, or along fence rows and roadsides. The compound leaves are alternate and have 3 leaflets oval or egg-shaped, rounded or broadly pointed at base, pointed at tip and usually with a few teeth on the margin. The end leaflet is long-stlaked and the side leaflets are almost stalkless. The fruit is white.
Be sure to review the pictures we have online here as well as follow the links we have to other sites with more pictures of poison ivy, poison oak, and poison sumac. You can find the pictures section at http://poisonivy.aesir.com/view/pictures.html. Also, look at the section Is it Poison Ivy? where we look at a number of poisonous and nonpoisonous plants from many areas of the country. Learning how to properly identify poisonous and non-poisonous plants is your best defense always. Even better than Roundup.
Now for what it is about the plant that is so toxic to so many. There is a secondary chemical in these plants called urushiol oil which is a sticky chemical which when in contact with skin bonds with the lower skin cells and causes a delayed allergic reaction. This oil is not found on the leaves but is actually found in resin canals in the leaves, stem, vine, and root. Just brushing against a leaflet will not transfer the oil to you unless there is damage to the leaflet. There has to be some means to cause the oil to escape. Unfortunately, the leaflets are quite fragile and easily broken. Here is a great technical paper on the secondary chemical: Secondary Compounds Within the Anacardiaceae. There is no way for one to come in contact with urushiol oil just by being near the plant unless of course its burning. Urushiol oil can become airborne if the plant is burned and if inhaled can cause a very serious reaction in the lungs, on the skin, eyes, etc. We discuss and give references on urushiol oil and transmission on the Q&A Board. I recommend that you perform a search using the keywords urushiol oil to see those threads and review the reference websites.
Many ways that people come in contact with urushiol oil without coming in contact with the plant is by handling pets who have the oil on their fur, tools used to work around plants, clothing that has accidently come in contact with the plants. You don�t have to actually touch the plant but you do have to come in contact with urushiol oil to get the rash. Proper cleanup is imperative after coming in contact with urushiol oil including fingernails, shoes, clothes, pets, etc. Soap and water is generally sufficient to clean off the oil but make sure that you use sufficient amounts of water. Go to this page to learn how soap works and why it works to remove oil so well.
You are welcome to upload pictures of the plants in question for identification. You can upload individual pictures or an archive such as a zip file at the uploads page. As for that palmated plant, if it looks like virginia creeper based on what you�ve seen here then it likely is virginia creeper. The palmated leaf is a key characteristic of that plant. Virginia creeper does have oxalates which some people are allergic to and so it can cause a dermatitis. This is not common though. Here is a response with reference website I posted on the Q&A board about virginia creeper: 5 leafed vine?. I have come to rely on the California Poison Control website and hope that it stays around for some time to come. If anyone reads this message lives in California, please go to the California Poison Control website and read about how you can help to keep it running.
Now here�s a tip that is probably the most important. "Enhance your calm". The mind while being wonderful is also destructive to our body. You stress and it can send histamines to the skin and voila � rash. You scratch and it can send histamines to the skin and voila � rash. Here is another message I replied to with reference sites: Don�t Stress Over That Rash.
So how do you deal with the "evil weed" as some put it? Here are my simple tips:
- Learn, learn, and learn some more. Grow confident in your proper identifications of the plants in your yard and around you.
- Take precautions such as long sleeves, pants, boots, vinyl gloves when handling questionable plants
- Don�t be afraid to spray. Roundup, Brush-B-Gon, Crossbow and other herbicides work well. READ THE LABEL for any herbicide you do use.
- Don�t rely on just heresay about what you are seeing. Learn it. Know it.
- Leep a calm head about the process. Plan out in advance how you will attack an area with poison ivy or oak in it.
Here�s an anecdote or two just to round out this post:
When we first moved into this house 10 years ago, the contractor working on the house swore that he knew intimately what poison oak looked like and we �had it� growing up a sycamore. Well now that I actually know what the plants look like, boy was he ever wrong. That healthy vine is virginia creeper. I pull the stuff by the ton every year and no rash. Now what we do have is a healthy crop of poison ivy and until I could recognize it, I was guaranteed no less than 4 rashes a summer season.
Final anecdote. I can�t work on this website for an extended period of time without having to scratch. Seeing all those pictures of poison ivy, oak, and sumac as well as responding to messages seems to cause something to trigger and I�d swear I�m covered with poison ivy rash on large parts of the body. Of course, once I finish working on the updates I�m back to normal. (Now just what does that say about my mind?) I bring this up as it points out the power of the mind. Stay calm. Stay in control. Even if you do come in contact with urushiol oil, there�s no guarantee you�ll have a bad rash. I�ve had brutal outbreaks but none serious in the last year or so. I know what the plants look like. I clean up well after handling. And I don�t stress over the rash.
As for cutting the vine, make sure that you are well-suited (long sleeves, pants, vinyl gloves, boots) for the job. Be prepared to clean up properly. And don't use powered tools - a bow saw will do the job without spitting little bits of plant and oil all over. Yes you can use Roundup but the surest method will be to get the root up out of the ground. Brush-B-Gon is noted to work well to kill the plant but I've had quite a bit come back up (user error?) so I prefer to get the roots up as well. Here is a message I left here on the Q&A board about pulling poison ivy from a garden, I think the precautions and clean up would work well for you. What can I do about poison ivy?
I hope the information above helps you, Alan, to better understand what may or may not be growing in your backyard. If you are still having problems with the old timers, ask them where they got their information. Personally, I trust well-known and trusted botanists, dermatologists, and other respected authorities.
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