What trees (if any) have roots that produce natural toxins that inhibit the growth of underplantings?

Reply to post by JeanB, on March 31, 1999 at 10:15:04:

Black walnut produces an allepoathic substance called juglone which inhibits growth of other plants. Tomatoes are known to be particularly affected.

This subject cropped up once before, but I didn't find it within this topic. If you search through archives of variuos topics here or on other tree sites you might find the thread.

Reply to post by JeanB, on March 31, 1999 at 10:15:04:

Generally speaking, most of the trees in the Juglandacea family produce juglone, a growth inhibiting compound. The black walnut is one of the best known, but other walnuts, hickories and pecans also produce some of this compound.

A web search on 'juglone' on Alta Vista turned up over 200 files.