Poison oak (Toxicodendron diversilobum) infested my mountain home where the brush and forest was dense second growth. During the growing season, the plant produces leaves in groups of three, its distinguishing characteristic. Once you recognize it, leafy plants are easy to spot and avoid. Problems arise during fall-winter dormant season, when poison oak is nothing but bare sticks. Lots of folks have problems after cutting brush and firewood because poison oak is so hard to spot at that time. When the dormant sticks are cut they weep, and it’s this fluid that is often the cause of off-season rashes.
Every spring when the new oily glistening foliage popped out I’d get unexplained rashes. Eventually I learned it was caused by our big dogs with thick fur that were running through the brush after wildlife. Later, the dogs came in the house or I gave them a big hug and voila, a rash popped up from oil that accumulated on their fur that gradually declined as new leaves age to drier maturity.
Poison oak contains urushiol, which causes contact dermatitis with intense itching that evolves into dermatitis, bumps and blisters. Often urushiol exists under the skin or within blisters so scratching simply allows for it to spread into new tissue. Inside where my arm bends at the elbow always seems the worst. It’s because when you bend your arm, the two parts come together so a rash on the inside of the forearm is directly contacting healthy skin at the bicep that soon develops a new rash. For this same reason, even a single poison oak rash on a male can present similar risk of spread from hands to private parts. Women will find the inner thigh a common rash location.
Be aware that fires that burn poison oak will carry urushiol in the smoke. Breathing it can cause an allergic reaction in the lungs, mouth, nose or esophagus. Often it’s inadvertently included with kindling can make camp fire smoke potentially dangerous. It has been a notorious problem in burn piles after clearing brush as smoke carries urushiol into the lungs.
After too many rashes, I went to war on the poison oak around the home site. Cutting just acted like renewal pruning and they came back bigger and badder than ever. Digging out the roots in rocky clay soil was nearly impossible because some always remained to restart the plant.
My ultimate solution was Roundup for brush, which is formulated to work best with woody plants like poison oak. It is taken in through the leaves through photosynthesis so treatment is best in the season when they are growing quickly. I found great success spraying when those early fast-growing oily leaves pop out and sap is free flowing to help translocate it to the roots. Give the plant a few weeks to die and it won’t come back.
I don’t like chemicals, so I treat the Roundup with kid gloves, spraying once as plants come into leaf until flowering. I do not use it if there is the slightest breeze. I’ve curled a big thick sheet of cardboard to stand behind the poison oak plant I’m after so there’s no drift onto adjacent soils or plants.
Three seasons later I’d surgically dispatched virtually every poison oak in the area around the house. My visitors no longer had to keep an eye out and the dogs were suitable for hugging. But I will forever keep an eye out for those three leaf signs that a new poison oak has grown from seed, flown in by birds to contaminate my personal, rash-free zone.
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Maureen Gilmer is an author, horticulturist and landscape designer. Learn more at www.MoPlants.com
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