Almost inevitably, when you see the damage it's too late to do anything but you can try to prevent a repetition next year.
We treat the fruit and veg patch very differently to the rest of a wildlife-friendly garden, where our "friends" and "foes" roughly keep each other in check. The veg garden is much more controlled and your crops attract pests and diseases you need to stop. The first rule is keeping the ground clean and tidy, throughout the year.
Start now to save next winter's cabbages from slugs. Keep removing plant debris. Clean up rotting kale and cabbage leaves that shelter slugs and their eggs. Molluscs lurk among roots, so when cutting a cabbage, remove the whole plant. If the ground's frozen, go back later and dig up the stump.
Decaying leaves and brassica stumps shelter other pests, especially cabbage aphids, the grey-green flies that congregate on the underside of leaves. They'll be at their peak over the next few weeks.
You'll sometimes find cabbage aphids in wild or garden brassicas. Eggs are laid in brassica stalks in the autumn and hatch out in April. They then feed on wild and garden brassicas during the summer and build up huge populations by reproducing parthenogenetically. In the late summer, they fly off to other cabbage plants where a sexual generation lays next year's eggs.
So clean up and compost all the debris where eggs will have been laid to stop a new generation hatching in April. Birds can also rummage around in bare soil to pick up eggs.
However frustrating slugs and aphids may be, it's heartbreaking to see the leaves of a once-glorious plant stripped bare. Cabbage white butterflies are to blame. In spring, small whites start laying single eggs as close to the centre of host plants as possible, and produce three generations a year. A large white causes much more damage by laying batches of up to 100 eggs on one large plant.
Maddening though they are, cabbage whites are fascinating. After devouring a sprout leaf, each caterpillar trundles off to pupate on a sheltered place nearby - a fence or wall. The adults can migrate hundreds of miles. Researchers have identified different migration routes and have proved second and subsequent generations on a particular flight path are genetically programmed to continue on a particular journey.
Intrigued as I am by this, I'll continue to cover my brassicas with fine insect net to foil the butterflies. An adult can lay eggs through a net, so leaves shouldn't rub against it. An alternative biological control is available, but is expensive and tricky to use.
The final challenge is stopping sprouts from being "blown" instead of forming tight, tasty buttons. The general advice is to grow sprouts in firm ground and lash them to short sticks to prevent wind-rock. This is one of these pieces of gardening advice that's repeatedly given, but never explained.
One possible reason is that, as effectively annual plants, sprouts can't develop as large a root system as perennials. They are tall, possibly taller than their roots can support, so they need to be firmly anchored. Fine, but why should rocking cause blown sprouts? Are small root hairs being damaged, making the plants stressed, thereby causing a form of bolting? I've come across no research to back this or any other explanation, but will continue to keep my plants firm.