North American Fruit Explorers mailing list at ibiblio

["Donna &/or Kieran" <holycow@cookeville.com>]

Jim Fruth asked about degradation of poison ivy over time.
   I seldom react to poison ivy at all, and for the last 14 years we have 
lived in a place that is crawling with it.  However, once in a while in the 
winter time I get it, almost always a day or two after digging in an area 
where it grows.  Apparently the sap from the cut vines or roots delivers 
more urushiol than merely brushing the surface of the leaves.  Well, one 
winter I found myself with a rash on my left wrist every single Monday.  It 
happened every week for at least a month.  I finally figured that I must 
have gotten the sap from a cut plant on the cuff of the beat up jacket I 
wore at home, and it stopped happening after I washed the jacket.
   So I don't think the chemical necessarily breaks down with the mere 
passage of time.   However, sunshine might break it down.  I doubt the inner 
sleeve of my jacket had much sunshine exposure.  Or it may be that the 
urushiol evaporates.  A low dose from brushing the leaf may have wafted away 
long before the dose delivered by the dried sap.  Or the sap may have held 
the urushiol in a way that could be accessed by my wrist rubbing against it 
for hours.     Donna