If you are growing cabbages, kale, broccoli, cauliflower or other brassica plants, it is a really good idea to protect them before cabbage white butterflies start laying their eggs!
During the summer, cabbage whites tend to lay 2 or 3 times, depending on the season. They love brassicas, and will lay their eggs on the leaves of cabbages, kale, cauliflower, broccoli, turnips, swede so that when the caterpillars hatch they have an instant supply of food – your veg plants! The caterpillars can quickly destroy a plant, and the best method of protection is to prevent the butterflies from laying their eggs on your plants in the first place. Here are 3 things you can do:
Net your brassicas with an insect proof mesh netting
Make sure the brassica net is propped up by hoops that are as high as the plants will get so that the net can stay there for the whole season. You can also prop the netting up with bamboo canes topped with jars. For broccoli, cavolo nero, red russian kale, and sprouts, 1.5m tall is about right. For cabbages, cauliflower, romanesco, turnips/swede and curly kale, 60-70cm would be fine. Choose mesh netting as pictured for best protection.
Plant nasturtiums as a sacrificial crop nearby
The butterflies will be more likely to lay their eggs on the nasturtiums and the caterpillars will destroy the nasturtiums rather than your brassicas.
Inspect leaves regularly and remove eggs/caterpillars
This is a bit of a chore and not always the most pleasant job, but with some kitchen paper and a bucket you can wipe off eggs from the underside of leaves before they hatch. They are usually very small, in clusters of little green, yellow or dark green eggs. Sometimes individual eggs laid more sporadically are white/yellow. If you find baby caterpillars have hatched, you can remove them (pick them off and pop them in a bucket) and leave them somewhere for the birds to eat or kindly pop them in a patch of nasturtiums somewhere else!