We often speak to our customers about Cabbage White Butterflies as they can be the bane of allotment holders over all parts of the UK. Although the butterflies themselves don’t do the damage – it’s actually the caterpillars which can cause havoc – eating their way through your crops so there is only a skeleton of the plant left.
It is for this reason that we have taken the time to find out for you everything there is to know about these devastating pests and helpful hints and advice on how to stop them in their tracks and protect your crops.
The first thing to do is identify a cabbage white . . .
What Are Cabbage Whites?
As the name suggests, the favourite food of these white butterflies is cabbages but they are happy to tuck into any brassicas such as broccoli, cauliflower, kale, sprouts etc which they can find. They are also attracted to other vegetables, such as turnips or swedes, as well as to some flowers, including some ornamental Cruciferae and nasturtiums.
These butterflies are most active between May to October . . . you’ll get your first clue that your crops are being targeted when you see holes in the leaves and the presence of caterpillars.
The butterflies will lay their eggs on the underside of the leaves and after about a week to two weeks the larvae, or caterpillar, will emerge ready to tuck into everything they can find. From that point on the aim of the caterpillar is simply to eat until they are ready to pupate – as a result these pests can easily devastate your crops if you don’t take action.
Cabbage White Butterflies will lay eggs either twice or three times a year if the weather is favourable, with the last egg laying of the year being in late August to September.
Here are the basic features of the three types of Cabbage Whites which you might find visiting your garden . . .
Small Cabbage White Butterfly / pieris rapae
- The Small Cabbage White butterfly is white with a pale green tinge on the underside of their wings and grey-black spots on the upper wings. It has a wingspan of approximately 3-4.5cm.
- The butterfly will lay single, pale yellow eggs The caterpillars are a pale green colour and are covered in short, velvet-like hairs.
- Less voracious feeders than the Large Cabbage Whites - the larvae of the small whites will tunnel into the hearts of cabbages – so even though less eggs are laid just a handful of larvae can do serious damage to your crops.
- These Small Cabbage White Butterflies will not survive the winter.
- The caterpillars are either a yellowish green or a brownish green and appear hairless.
- The caterpillars of these moths, like the Small Cabbage Whites, like to bore into the heart of the cabbage.
- The Cabbage Moths will over winter in the ground.
Large Cabbage White Butterfly/ pieris brassicae
- The Large Cabbage White butterfly is similar in appearance to the Small Cabbage White - white with a pale green tinge on the underside of their wings and grey-black spots on the upper wings. The wingspan of this species is larger, up to approximately 5.5cm.
- The butterfly will lay groups of pale, golden yellow coloured eggs, between 40-100 at a time.
- The caterpillars are black and yellow and have obvious hairs on their body.
- Voracious feeders when compared to the Small Cabbage Whites - the caterpillars of the Large Cabbage Whites will stay mostly on the outside of your crops, eating the outer leaves.
- These Large Cabbage Whites are unlikely to survive the winter.
Unfortunately, having one type of butterfly in residence in your garden doesn’t stop the others from coming to feast on your crops too! In fact you could have all three caterpillar culprits which will result in your crops having holes in the outer leaves, when you cut into the crops you will find damage to the inner leaves and you’ll find copious amounts of caterpillar ‘poo’ on your plants.
How To Protect Your Plants From Cabbage Whites
Although gardeners will talk about Cabbage White Butterflies, it is, in fact, when they are in their caterpillar stage that they will cause damage in your garden.
You need to be vigilant to prevent your crops from being damaged by these pests, so you should be checking the crops they like to feed on from spring onwards – if you can catch them early you should be able to prevent a damaging infestation.
You should check the leaves of your plants for caterpillar eggs and remove them if you find any. If the eggs have hatched and your plants are covered in caterpillars then you can either remove these manually or use a hosepipe to wash them off.
However, if you had had problems with these pests in previous years, you could take preventative measures early and reduce your need to spend time searching out these butterflies or caterpillars.
A Physical Barrier
One way to provide instant protection is to grow your brassicas under a material which the butterflies can not get past to access your plants. This can be something as simple as horticultural fleece, an insect netting such as enviromesh or a fine net, such as our butterfly netting. You should note, that when using a net that you need to regularly check that the plants haven’t grown big enough to touch the net – if they do then the butterflies will get their chance to lay their eggs and the damage will start.
Our Horticultural Cosygrow Fleece is a good option as you can use it for different functions through the year, so will get excellent value for money.
Enviromesh is a superfine nylon mesh which has been specially designed to protect crops from insect damage caused by cabbage whites, carrot fly, aphids, etc etc.
This fine mesh lets your plants remain naturally watered and ventilated whilst preventing them from being attacked by pests.
This 1.8m wide material can be bought in any length and is light enough in weight to place directly over plants or it can be used to cover a frame.
Again, take care when anchoring this material to prevent leaving holes for invaders to find.
Butterfly Netting is a strong, moulded black plastic net which is UV stabilised so should provide at least 5 years of use.
A Biological Control
If you don’t want to create a physical barrier to protect your plants, then you could try using a biological control. For example, Nemasys Fruit and Veg Nematodes Protection contains a unique mix of different nematode species to target a broad range of pests, including caterpillars, so is perfect for protecting against the caterpillars of the Small and Large Cabbage Whites. Although this treatment is relatively economical – you can spend less than £10 to control an area up to 60 square metres, it has to be applied missed with water and the spray needs to come into contact with the pests – pests not directly sprayed will not be controlled.
Grow Magnet Plants
You could grow so called ‘magnet’ plants in other parts of your garden - away from your crops – which the butterflies will be attracted to and that you are willing to sacrifice, in-order-to protect your crops. The butterflies can then lay their eggs of these plants, caterpillars can emerge and eat these plants rather than tucking into your crops. Although this type of pest protection does have it’s drawbacks . . . by planting other plants which attract the butterflies are you just encouraging the butterflies into you garden? . . . if your magnet plants get full of butterflies and caterpillars, will others just move to the crops you were trying to protect??
Encourage Natural Predators
Another prong of attack to fight the Cabbage Whites, is to encourage their natural predators to take up residence in your garden – this only works if their predators will do considerably less damage than the Cabbage Whites would do.
The obvious natural predator to the caterpillars are birds – but they need to catch the Small Cabbage White caterpillars before they tunnel their way into your plants!! And the caterpillars have a cunning self-defence mechanism – having eaten their way through your crops they will be full of mustard oil, which makes them unpalatable to most predators, so you’ll find birds will leave them alone if they have reached this point in their lifecycle.
Another major predators to caterpillars are social and parasitoid wasps. You can encourage these into your garden by planting herbs or flowers, such as dill, fennel, cilantro or queen anne’s lace etc which these wasps feed on. Good to note is that parasitoid wasps shouldn’t sting whilst some social wasps will sting but usually only if you get too close to a large colony.
There are both organic and synthetic pesticides available which can be used to control the caterpillars of the Cabbage Whites – but it’s worth noting that pesticides will need to be used more than once for the treatments to be effective.
Always check that the crop you are going to use the pesticide on is listed on the pesticide label before you choose one and check the instructions carefully as you may need to leave the crops after treatment for a set length of time before you can harvest. It should be noted that there are still some very powerful, toxic chemicals in some pesticides that could affect a range of insects, including ones which we need such as bees, so always read the small print and ideally choose a pesticide that has been approved for organic gardening and is based on natural compounds such as pyrethrum.
Once the caterpillars have eaten their fill of your crops, they will try to find somewhere in your garden which is sheltered and safe where they can pupate. They will pupate for around two weeks in the summer, or eight weeks in the winter so if you wish to reduce their numbers whilst they pupate is a good time – so check your fences, shed walls, under windowsills, broken bark, tree trunks etc to find and remove them.