Poison ivy can invade even the most well-groomed landscape, and it presents a special challenge to those of us who are sensitive to it.
It’s easy to come in contact with poison ivy when doing routine gardening tasks.
In addition to the typical skin rash and itching that can result from touching the plant, highly allergic people must be careful not to inhale smoke when burning poison ivy in brush piles, or contacting pets with the toxin on their fur.
The entire poison ivy plant contains the toxic oil urushiol, a colorless or slightly yellow oil found in the leaves, stems and roots. The oil can remain active for months on objects. It can be picked up on tools, clothing and the fur of pets.
Therefore, anything that may carry the oil should be carefully washed. Even dead plants or roots may cause allergic reactions for a couple of years.
Poison ivy is most dangerous in spring and summer when oil content is highest. For those sensitive to the oil, a skin rash resembling small insect bites, will appear within 12 to 48 hours, but a reaction can take up to two weeks to occur.
This rash develops into a more severe rash and blisters. Scratching the rash spreads it.
Poison ivy grows fast, quickly spreading itself by underground roots that can travel many feet in soft soils and mulch. Seeds are quickly spread by birds and other animals that eat the small fruits.
Poison ivy can get started in the landscape from seed dropped by birds, and may quickly become a widespread problem. It often grows in shrubs and groundcovers, making it difficult to control.
To eliminate poison ivy chemically, use an herbicide that contains glyphosate, triclopyr, or a 3-way herbicide that contains 2,4-D amine, dicamba, and mecoprop. We use Crossbow brush killer (a combination of 2,4-D and Triclopyr), mixed with water at the rate of 5 ounces per gallon, applied with a pump sprayer.
The challenge is to not spray desirable plants in your eagerness to kill the invader. Adjust the nozzle to get a narrow spray pattern, not a fine mist. Sometimes it’s better to locate the woody main stem, cut it diagonally, and immediately brush on the herbicide concentrate.
This method kills the plant roots without any spray drift. Be careful to clean your pruners afterwards!
Whether sprayed or applied to cut stems, herbicides work better when you use them at the right time. Poison ivy and poison oak are most sensitive to 2,4-D and dicamba treatments in late spring or early summer when the plants are growing rapidly.
Triclopyr offers the best control after the leaves fully expand in the spring and before leaf color changes in the fall. Glyphosate (Roundup) works best when applied in early summer.
Serious poison ivy invasions take time and patience to overcome, and you need to watch for seedlings in future years. If your yard is (or was) wooded, there can be lots of seeds in the soil.
Be careful about using shredded wood chips from tree trimmers as mulch; very often they can contain poison ivy berries or seeds. Make sure to protect yourself with long sleeves and gloves, avoid touching your face when weeding, and either wash or discard gloves after touching the plants.
Remember that even dead poison ivy plants can be very potent.
Steve Boehme and his wife Marjorie own GoodSeed Farm Landscapes, a design-build landscape/hardscape installer specializing in outdoor living spaces. More information is available at www.goodseedfarm.com or call GoodSeed Farm & Garden at (937) 695-0350.