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The three most common poisonous plants in our area are Poison Hemlock, Poison Ivy and Poison Oak.
Poison Hemlock is a biennial weed, meaning its life cycle is completed in two years. During the first year, the plant grows as a short -- less than 18 inches in height -- rosette with its leaves arranged in a cluster at the base of the plant, similar to a dandelion's growth habit.
In the second year, in March and April, the plant will still appear as a low-growing rosette but as spring progresses the plant will bolt/flower and send a flowering stalk from the base of the plant until it is about four to six feet in height. The flowers are umbrella-shaped and white in color.
It is often confused with Queen Annes Lace, which is also known as wild carrot or wild parsnip. Wild carrot is usually 18 to 24 inches in height when flowering compared to poison hemlock's towering height of 4 to 6 feet at the same stage. Poison hemlock will be less than 24 inches in height when it is not flowering.
The other key difference is that wild carrot has numerous, fuzzy white hairs along the stems. Wild parsnip will reach the same height as poison hemlock during flowering but will have yellow flowers and no purple coloration on the stems. The main things to look for are the reddish/purplish colors on the stems and an absence of hair on the stems. Once the plant begins to flower the stems become very purple which will cover most of the stem.
The entire plant is toxic including seeds. Handle these plants with gloves. If on your property, you can remove with a shovel but wear long sleeve clothing. The best time to control poison hemlock is with a chemical spray in the fall, including diquat, pelargonic acid, glysophate, or 2,4-D.
Poison Ivy is a common plant most of us are familiar with. Poison ivy is a vine that grows vertically as it attaches to various structures, but it also becomes a ground cover when it can't grow upwards. Leaflets are in groups of three and can be smooth, toothed or lobed.
This is different from another common native vine, Virginia creeper, which has leaflets in groups of five. The foliage of Virginia creeper turns red in the winter.
After coming into contact with the plant be sure to wash affected area with soapy water and apply over the counter medications like calamine lotion. You don't even have to contact the plant directly. The plant oil can get on tools, pets or clothing and when you touch them, you can pick it up. It can also be inhaled when it becomes a gas when poison ivy is burned. Glyphosate (Roundup and others) can be applied to foliage, or to the vine via cutting and squirting/wicking into the wound.
Poison Oak is similar to Poison Ivy. This plant releases oil (Urushiol) that cause rashes and blisters. It has a shrub-like appearance. It can grow 3 feet tall, giving it the appearance of a vine. Poison Oak has three leaflets like an oak leaf (as opposed to three leaves). In the spring and summer, it produces small white, yellow, and even green flowers.
Your best chance at avoiding a reaction is to treat poison oak within 10 minutes of contact. Urushiol is not water-soluble! Use strong soaps (like dish soap) and wash with cold water to keep the oils from spreading. Cleanse the area of contact within the first 10 minutes, then rinse off with cold water.
As urushiol can remain active for years, you will want to wash any clothes, items or furniture that may have come into contact with the invisible oily residue. If you do not treat the exposure immediately, treat the resulting itchy rash and blisters topically with calamine lotion, baking soda pastes, aloe vera and a number of commercial products. One tried-and-true remedy for itchy skin is oatmeal.
Again, application of glysophate can be applied to foliage or directly to the cutting area and squirting/wicking into the wound.
If you have a question about poisonous plants or any other plant, please contact the Penn State Master Gardeners at mifflinmg@psu.edu or call (717) 248-9618. When applying pesticides of any type, be sure to read the label and follow the instructions carefully.