Wired Magazine ran an article in their November 2004 issue about the appearance of a coca plant in Colombia that showed resistance to glyphosate (the RoundUp pesticide):

http://www.wired.com/wired/archive/12.11/columbia.html

The U.S./Colombia authorities have never publicly acknowledged its existence, but according to the article, all the growers in Colombia have switched to "Boliviana negra" -- the "Roundup-Ready" coca. Apparently, the original plant was discovered in a sprayed field, and cuttings were made from it, and were grown out like crazy. Seems it was a naturally-occurring mutation -- no signs of genetic manipulation. So much for Plan Colombia...

planned obsolescence by evolution.