Poison Ivy Hard to Identify, Just as Tough to Control 6/22/04

MANHATTAN, Kan. - Where poison ivy grows in the wild, children soon learn the saying “Leaves of three, let it be!”

Unfortunately, that compound leaf (three leaflets together) is about the only way poison ivy makes itself easy to identify, said Ward Upham, horticulturist with Kansas State University Research and Extension.

“The leaves themselves can vary. They can be dull or glossy. They can be different shades of green - even on the same plant. Their margins or outside edge can be smooth, lobed or incised like a saw. Leaf size can vary from plant to plant, although the middle leaflet is usually larger than the other two and is the only one with a long stalk. The smaller leaflets are always closely attached to the side of the leaf stem,” Upham said.

Got Poison Ivy?
Wash, Wash, Wash

JUNCTION CITY, Kan. - People can’t assume they’re immune to poison ivy just because they have touched it, but not developed an itchy, inflamed rash. They may just have come in contact with a poison ivy plant that hasn’t been damaged in some way.

“No surface on the poison ivy plant is toxic. The plant’s clear, oily sap is what causes the reaction,” said Chuck Otte, agronomist and one of the Kansas State University Research and Extension agents based in Geary County.

But, because of its place in nature, poison ivy usually has enough surface wounds and exposed sap to cause a rash, Otte warned. Just handling sap-contaminated clothing or tools can cause a reaction .

And, because that sap is oily, getting it off skin and clothing can be extremely difficult. In fact, washing in warm or hot water - even with soap - will simply help the oil penetrate skin better. Over time, repeated warm-temperature washings can also create the appearance that the rash is spreading. What really spreads is the toxic sap that the washings have not removed.

To minimize poison ivy’s toxic effects, victims must wash in lots and lots and LOTS of cold water and soap. They must clean any exposed clothing and tools the same way, he said.

“The sap is what’s called ‘marginally soluble.’ That means a little water will spread it. A lot of water can wash it off. To get an idea of how much washing that means, think about what it would take to clean an oil-and-vinegar salad cruet with cold water and soap,” Otte said.

Gardeners who grab poison ivy while weeding also bring sap to the plant’s surface, he said. A mower or weed eater can send sap and sap-covered plant pieces flying through the air in every direction.

Deer create openings for sap as they browse on poison ivy (a deer favorite). Insect pests do the same when they chew.

“In fact, if you burn poison ivy during a fall clean-up, the smoke will carry sap droplets along with the dust and ash,” Otte said. “That can cause serious problems for someone who’s sensitive to the toxin and inhales the smoke.”

After several hours of exposure to air, poison ivy’s sap turns black and becomes the dark residue often seen on the plant’s leaves. Despite this change, however, the sap remains toxic until it washes or wears away.

To make things more confusing, poison ivy also prefers partial shade, but will grow in full sun. Plus, it occurs in three forms:

* An upright, woody shrub that can grow in dwarf form or be up to 12 feet tall – about the size of some boxelder trees (which also have triad leaves).

* A creeping groundcover that can infest an entire neighborhood from a single big “mother” root.

* A woody vine that can climb trees, much like the five-leaflet Virginia creeper.

These variations are why correctly identifying poison ivy may require collecting a sample and getting help from a long-time gardener or county Extension agent, Upham said.

“Some people use an empty, clean bread bag. They put their hand and arm in the bag, break off the sample with their covered hand, and then enclose the poison ivy without touching it by just turning the bag inside out,” he said.

Gardeners have used a variety of ways to get rid of poison ivy. In many cases, however, the plant’s growth form has determined the best approach to take.

“If the plant is growing as a groundcover, some people prefer grubbing it out by hand, perhaps hoping to locate and remove the mother root,” the horticulturist said. “For grubbing to work well, however, the soil must be moist. And, to protect yourself, you need to wear gloves, a long-sleeved shirt and perhaps even long pants, because every part of the plant that contains sap can cause a skin reaction. You’ll need to wash the clothes and yourself as soon as you finish.” (See sidebar.)

A direct herbicide spray also can kill poison ivy’s groundcover forms and is the preferred way to eliminate the shrub forms.

“You’ll still need to be careful when you cut the dead shrub down and remove it,” Upham warned. “Unless worn or washed away, the toxin in poison ivy’s sap can stay active for years - even on gloves, shovel handles and dead plants.”

Retrieving or spraying a poison ivy vine that’s growing up a tree is a practical impossibility, the horticulturist said.

“The preferred method is to cut the plant off at the base and perhaps remove the stretch of woody vine that children could brush against – again, being very careful not to expose your own skin. Then spray the new sprouts as they emerge from the roots,” he said.

Poison ivy is a tough plant, however, Upham warned. Repeat applications may be necessary.

Herbicides that will control poison ivy include glyphosate (Roundup; Killzall Weed and Grass Killer; or Nutgrass, Poison Ivy and Vine Killer) or triclopyr (Brush-B-Gon Poison Ivy Killer or Brush Killer Stump Killer).

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.