While digging up, I found another reference to centuries-old "preserved" specimens causing contact dermititis in people sensitive to urushiol.
Here's the reference said about PRESERVED specimens (i.e., not weathered):
I'm surprised the urushiol remained potent far longer on outdoor plants (5 years) than on indoor unwashed clothing (1 or 2 years); but one take away is that just killing the plant doesn't solve the problem of needing gloves to remove the huge piles of dead plants blocking access.
But, I'm liking the bulldozer idea more and more as we speak ...