The Cabbage white butterfly continues to cause devastation to brassicas at this time of year. Although it is best to remove caterpillars and eggs as soon as they are seen, you may not get to your crop in time to prevent this.
A good spray with Fruit and Veg Protection will help, but for those of you who prefer not to use a spray, the alternative is to cover them with Marshalls Crop Netting which will prevent caterpillars getting near your crop.
Ensure the net is not touching any leaves as this may allow butterflies to deposit eggs through the net and onto the leaves. An Extra Fine Insect Netting should protect your Brassicas from all the tiny flying insects that can destroy your crop.