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Friday 22 September 2023 Dublin: 11°C
In the garden How to fight back (nicely) against the caterpillars eating your plants
Growing brassicas like kale or cauliflower is basically a war between you and the creatures that want to eat the plants, writes Michael Kelly of

EVERY YEAR AT around this time, I am reminded that growing any of the brassicas (kale, cabbage, cauliflower, sprouts etc) is basically a war between you and all the creatures that want to eat the plants. I know that doesn’t sound very calming or nature-loving, but there you go.

Even though kale is one of the easiest of the brassicas to grow, it’s still vulnerable to caterpillars, particularly the tender cavolo nero or Italian kale that I love above all the other kales.

Sometimes I think that ‘brassica’ must be latin for ‘oh my god what’s eating my fecking kale?!!”.

The primary enemy is the cabbage white butterfly, a white butterfly which dances prettily around the veg patch from spring until autumn. It lays eggs on the leaves of the plants and those eggs turn into larvae (caterpillars) that feast on the leaves. An infestation of caterpillars can completely strip a brassica plant of leaves if given the chance.


As an organic grower, there are a limited but thankfully effective array of weapons at your disposal to deal with the Cabbage White. A physical cover to prevent the butterfly from landing on the leaves is the best of all. I use a net called bionet which I drape over the plants and pin down with bricks or stones at the edges.

But be careful – it needs to be really well secured, for the Cabbage White is a crafty opponent and has literally nothing else to be doing with its time other than trying to find gaps so it can flutter in to lay eggs on the leaves. I looked out the window of house one day last week and saw a butterfly flying around, trapped inside the netting. And GIYing is supposed to be relaxing?

The second weapon is to inspect the underside of the leaves for the eggs (little clusters of skittle-shaped yellow eggs) or later in the season to pick off (or wash off with a hose) the caterpillars themselves. The caterpillars of the small cabbage white butterfly are green, while those of the large white are yellow and black.

This clearing off of caterpillars can be an increasingly futile effort if they’ve got really established. I find I start the season with great intentions to keep checking the leaves but I become less careful later (ironically, since this is when vigilance is most needed).

If you want to turn the war really nasty (but still keeping away from chemical interventions) there’s a bio-insecticide approach you could take – a bacteria called Bacillus thuringiensis – which comes in powder form and is added to a watering can (see below).

A garlic spray can also be somewhat effective and let’s be honest is a little less brutal. Equally, planting lots of flowers around your veg patch will provide a heady source of nectar for beneficial insects (such as wasps) and insect eating birds.

The Basics – Bacillus thuringiensis

Bacillus thuringiensis (Bt) is a naturally occurring bacteria, common in soils, that causes disease and starvation in certain insects, notably caterpillars.

Discovered in the 1900s, it has been available as a product for use in organic growing since the 1960s and multiple tests have shown it to be safe for use on crops. It is a good example of a natural, targeted pesticide that is lethal to a specific range of insects, but not to other beneficial insects, animals, birds or humans.

Bt works because of its active ingredient – a crystal protein which messes with the digestive system of the insects and starves them to death. It is the genes of this active ingredient that has been genetically modified in to some crops such as corn, causing some controversy (somewhat unfairly) for Bt itself as an organic control.

Bt generally comes in powder form, and is added to a watering can or sprayer to be sprayed on to the leaves of brassica plants. The timing of the spraying is crucial – Bt is a stomach poison for insects, so the caterpillars have to actually eat it for it to work. The time to spray is after the eggs have hatched in to caterpillars but before they start to pupate (turn into a cocoon).

Make sure to spray on the underside of leaves too. The best time to spray the plants is early morning and evening, since the product is vulnerable to sunlight. Bt is generally safe, but you should still follow all the safety directions on the label about mixing and cleaning up afterwards.

Recipe of the Week: All Day Eggs

This recipe is adapted from the Hemsley & Hemsley cookbook. It’s a particular treat at this time of the year when we’re using all our own veg (and particularly flavoursome with our own tomatoes).

Interestingly, I’ve tried making this recipe with tinned tomatoes earlier in the year, and it just doesn’t stack up. You can use kale or spinach leaves instead of chard, but I think the chard stems add a lovely pop of colour.

It’s a great weekend breakfast (takes about 30-40 minutes to prep and cook so you’re unlikely to try it mid week) or a weeknight supper. You literally can’t get a healthier or more delicious plate of food.

Serves 4.


  • 1 tbsp butter
  • 1 onion, chopped
  • 2 large garlic cloves, chopped
  • 1 large green or red pepper, or a mild chilli pepper (like Hungarian Hot Wax), chopped
  • 1 tsp cumin seeds, ground
  • 6-8 large tomatoes (about 450g) roughly chopped
  • 1 tsp balsamic vinegar
  • 200g rainbow chard, stalks finely chopped and leaves sliced into ribbons
  • 4 eggs
  • a small handful of fresh herbs like parsley, coriander or dill
  • small handful crumbly feta or dollop yoghurt
  • a pinch of cayenne pepper or smoked paprika
  • a squeeze of lemon juice
  • sea salt and black pepper


Heat the butter in a large frying pan and gently fry the onion for 5 minutes.

Add the garlic, red pepper and cumin and cook for a few minutes.

Add the chopped tomatoes, chard stems, balsamic vinegar and 250ml water, stir and bring to a simmer.

Pop the lid on and let everything cook down for 10 minutes to make a chunky sauce.

Stir in the chard leaves and cover the pan for five minutes to allow them to wilt.

Take the lid off, season to taste and, if needed, leave to reduce again with the lid off for a few minutes for the sauce to thicken.

Push the vegetables aside using a spatula to make a small gap in the sauce and crack an egg in. Repeat for the other three eggs.

If you pop the lid back on the eggs should be ready (whites set, and yolk runny) in about three to four minutes.

Scatter over some fresh herbs, a dollop of yoghurt or feta and finish with sprinkling of cayenne pepper or paprika and a squeeze of lemon juice. Leftovers would be great next day, but we never have any…!

© GIY Ireland 2018 – all rights reserved.

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