Dear MG: about twenty years ago the KGB arranged murder of an anticommunist by having
him jabbed in back with umbrella of which the hollow tip carried a pellet of ricin, which is a
derivative of Castor bean, and easy to make. And in that case easy to use. The victim did
not realize his skin had been penetrated, and would have had no way of knowing he needed
special treatment very quickly.
So "weaphizing" an extract from a common plant sounds very easy and feasible to me.
Of course there would be limits on how easy it might be to get intended victim into right
place at the right time. Good only in limited circumstances. As far as I know the Russians
used it only once for that reason.

Here's URL about the Cold War episode in London.
http://asia.cnn.com/2003/WORLD/europe/01/07/terror.poison.bulgarian/