Just to clue us in, by "bean flies" do you mean the tiny white flies
(about
2 mm in length) that can be found in plague numbers on the foliage of
carrots,
tomatoes and curcubits?

Apart from sticky yellow strips to attract and hold whitefly, I frequently
hear Comfidor suggested as an effective spray.

I've seen tiny spiders (what we'd call money spiders) catch white flies,
so
insecticides would kill off the spiders, too.
--
John Savage (my news address is not valid for email)

Hi John,
No the "bean flies" I am referring to are small black flies that lay eggs on
the leaves almost immediately the plants emerge. The resultant larva burrow
into the stem and eat the inside of the plant. The plant either dies or
survives to give only a very poor crop. I was led to believe that the phenol
did not stay too long in the plant but mainly disguised it from whatever
senses the flies used to locate it.
Thanks for your input,
Dan