To keep cabbage whites off you can use a 8mm net, it does not hold off cabbage moths however. While trap crops are not always effective having some outside the net will give the butterflies somewhere to deposit their eggs and somewhere you can find and destroy them!
7mm mesh 'butterfly netting' is the usual size sold in the UK, Skandi. It works well but, as you say, butterflies will lay through it if leaves are too close to the net. It is a bit of a pain to erect and makes harvesting tricky but also keeps the woodpigeons off which are the biggest problem for me.
A trowel in the hand is worth a thousand lost under a bush.
I use sacrafical nasturtiums to lure the butterflies away from my brassicas. They only have so many eggs to lay so if nothing else it reduces the number laid on your food plants and gives the caterpillars somewhere to live ensuring that the next generation of pretty pests survives.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
Me too Wild Edges have a whole block.of nasturtiums which take the black.fly from the broad beans and the eggs from the cabbage white,bees love them and I use the flowers and leaves in salad and pickle the seeds as soon caper substitute. Absolute little belter of a companion plant.
I hadn't expected to be growing psb this year but Wonky gave me some plants so I've had to fit them in where I can and there's no chance of netting until the sweet corn is finished so every morning I'm inspecting the backs of the leaves for butterfly eggs ... thank goodness she only gave me four plants
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
I think you have three problems there, those "eggs" are aphids, if you zoom in you can see the legs, they are not causing the holes however.
If you look JUST above your thumb on the underside you can see an egg, I think it's a small white butterfly egg, it may be causing the damage but it looks more like cabbage moth damage to me.
I'm in awe of you, Skandi! What distinguishes the moth's damage from a small white?
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.