In article , Robert the_devils_advo
writes
*
I know Derris is suggested for organic growers but it is more
deadly than some of the chemicals you can use and is not selective,
i.e. it kills all insects, friends and foes. I wouldn't use it

You are right not to use Derris for the reasons you quote.
It is not 'suggested' for use in organic systems.
My way of dealing with greenfly and other aphids is to use a foliar
application of nettle infusion. There's an urg FAQ on that method at:
http://www.nugget.demon.co.uk/MetaFAQ/nettle.html
--
Alan & Joan Gould - North Lincs.