Horticulture New: Perilous plants of summer

By Adam Leonberger, Published:

As the summer season comes into full gear and schools are out of session, many people will have the pleasure of experiencing poison ivy’s effects. I’ve even had to remove it from around the county office this past week.

Unfortunately, poison ivy, oak and sumac don’t grow with little picture ID badges around their stems, so you have to know what to look for. The famous rule “leaves of three, let it be” is good to follow, except that some of the plants don’t always play by the rules and have leaves in groups of five to nine. 

What to look for

A woody perennial weed frequently found in orchards, forests, and landscapes, poison ivy reproduces by seed, which may be spread by birds and by creeping stems that can spread a long distance in a season.

The plant can be either an upright shrubby plant 2 to 3 feet high or, more commonly, a vine that climbs on trees and fences. Plants are distinguished by the three leaflets on each leaf. Leaflet edges are irregularly toothed. The vines will usually have a proliferation of roots with the older vines looking like a hairy mass.

Flowers are small and insignificant, fruits are small (1/8-inch in diameter), round, and waxy white in color. Plants may be spread through birds eating the fruit and spreading the seed in their droppings. Leaves develop attractive autumn coloration of reds and orange.

Approximately 85 percent of the population will develop an allergic reaction if exposed to poison ivy, oak or sumac, according to the American Academy of Dermatology. Usually, people develop sensitivity to poison ivy only after several encounters with the plants, sometimes over many years. However, sensitivity may occur after only one exposure. 

The cause of the rash, blisters, and infamous itch is urushiol (pronounced oo-roo-shee-ohl), a chemical in the sap of poison ivy, oak and sumac plants. Because urushiol is inside the plant, brushing against an intact plant will not cause a reaction. But undamaged plants are rare. Stems or leaves broken by the wind or animals, and even the tiny holes made by chewing insects, can release urushiol. 

Avoiding direct contact with the plants reduces the risk of contamination, but doesn’t guarantee against a reaction. Urushiol can stick to pets, garden tools, balls, or anything it comes in contact with. If the urushiol isn’t washed off those objects or animals, just touching them could cause a reaction.

Animals, except for a few higher primates, are not sensitive to urushiol. Also be sure not to burn the plant as smoke from burning poison ivy can cause reaction not only to the skin but also to the eyes, throat and lungs.

Getting rid of the plants

Poison ivy, oak and sumac are most dangerous in the spring and summer, when there is plenty of sap because the urushiol content is high and the plants are easily bruised. However, the danger doesn’t disappear over the winter.

Dormant plants can still cause reactions, and cases have been reported in people who used the twigs of the plant for firewood or the vines for Christmas wreaths. Even dead plants can cause a reaction.

Never burn the plants, even if they are dead, and composting is not recommended either. The plants must be chopped into small pieces first, which just adds to the time you’re exposed to the plant and risk of a rash.

If poison ivy invades your yard there is no good or easy method to get rid of it. The two herbicides most commonly used for poison ivy — glyphosate (Roundup) and triclopyr (Ortho Poison Ivy Killer) — will kill other plants as well. Spraying glyphosate or similar herbicide products on the foliage of young plants will kill the poison ivy, but if the poison ivy vine is growing up your prize rhododendron or azalea, for example, the Roundup will kill them, too. 

It is possible to spray poison ivy without killing other plants if you pull the poison ivy vines away from the desirable plants and use a paint brush to wipe the ivy foliage with the herbicide, or use a shield (such as a funnel attached to the end of the spray wand) on the sprayer to direct the chemical exactly where you want it.

If you don’t want to use chemicals, manual removal will get rid of the ivy if you’re diligent. If you are going to pull the plants, wear plastic gloves over cotton gloves. You must get every bit of the plant — leaves, vines, and roots — or it will sprout again. It may take several seasons of a combination of eradication methods to finally kill the plant.

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