al wrote in message ...
I've just dusted with DERRIS powder some brussells sprouts plants suffering a caterpillar infestation.

Are there any alternative organic methods for dealing with caterpillars ?

Floating row covers to prevent egg deposition. Hand picking. BT which
is a bacterial control for the larvae of Moths and Butterflies and
sold as Dipel or Thuricide in many places.
It works best when applied early.