Urushiol oil [the toxin in poison ivy] stays active on any surface, including dead plants, for up to 5 years.
This includes on clothing too. Like the hunter who gets it again the next year and can’t figure out how. It was on his jacket. Or like me. After getting reinfected three times in the same place, I finally decided the evil demon urushiol was on my jeans and tossed out three pair (yes, they’d been washed, several times too.)
How bad can a poison ivy rash get? This bad. (Viewer discretion advised, seriously…)
Evolutionary theory says that nasty effects like these have survival value and increase the ability of the species to survive. Yet only a few mammals get a nasty reaction to poison ivy. Most animals are not affected at all by it. So, how does being toxic to humans help poison ivy survive when other animals can presumably eat it?
My theory is that poison ivy is just freaking evil…