While poison ivy is the most well known for its ability to irritate anyone that brushes up against it, there are plenty of other plants capable of harm. The biggest offender is wild parsnip. It’s a tall plant with mustard yellow flowers. Naturalist at Marr Park, Pam Holz, says if you come in contact with the plant’s oils on a sunny day, the chemical reaction can cause blisters. She adds the noxious weed will dry out in a few weeks, after which it’s harmless.