It is obviously too late now to save my Brussels sprouts and broccoli from the ravages of caterpillars. We used netting, but it was apparently not a fine enough mesh. But what about next year? I do NOT want to use the insecticides you suggest… a bit surprised that you did! Am always concerned about any poisons with food – but also fear their effects on non-target species… and the birds etc. which eat the larvae.
Close-woven mesh or fleece can be used as a barrier.
There is a biological control which contains bacteria that kill caterpillars.
Insecticides can be used in the period before the crop is ready for use. These have a very short withdrawal period of as little as one day. These are approved for use by the state authorities but everybody has a choice of using them or not. They are convenient for use with large numbers of plants where other methods are not practical.