Cabbage white butterflies are a major pest, particularly, of course, when it comes to your brassica crops. Cabbage white butterflies are a common sight in gardens. And like other lepidoptera, they can be very useful creatures to have around.
Butterflies and moths are crucial to a healthy garden ecosystem. They often play a role in pollination, and of course are an important part of the food chain. But cabbage white butterflies lay their eggs, and those eggs will transform into caterpillars that can munch their way through cabbages and other crops remarkably quickly.
What Are Cabbage White Butterflies?
Pieris brassicae is a type of butterfly known as the cabbage butterfly, cabbage white or large white. It is a close relative of Pieris rapae or small white. This type of butterfly is common throughout Europe, North Africa and Asia.
Cabbage white butterflies lay their eggs, which then pass through five larval instars before becoming the caterpillars you might recognise from your brassica plants. They then pupate and turn into adult butterflies. The males and females both have white winds with black tips on the forewings. The females also have two black spots on each forewing. The underneath of the wings is a delicate pale green/ whitish hue, which helps to camouflage the species when they are at rest.
How To Deal With Cabbage White Butterflies
Now you know what these are, and how to identify them, it’s time to think about what you should do about them in your garden. Of course, they won’t always be an issue. But here are some of the steps you should take to avoid a brassica massacre:
Be Vigilant and Pro-Active
The most important thing when it comes to pest control in an organic garden is staying alert. It is important to be observant, since it is only when you notice a problem that you can take steps to address it. If you do not remain vigilant, you are only likely to notice a problem once it becomes a major issue. But if you spot a problem as soon as it occurs, it will be far less problematic and easier to deal with.
As soon as you spot cabbage white butterflies flying around in your garden, it is time to start looking carefully at your crops to see whether you can spot where they have laid their eggs. Look over all your brassicas, checking for the clusters of eggs on the undersides of all the leaves.
You can wipe off the eggs from important crops to prevent a caterpillar infestation. However, bear in mind that it is not a good idea to eradicate wildlife. In an organic garden, your goal should always be to try to live in harmony with the other creatures that share your space.
One way to avoid encountering a severe cabbage white problem in your polytunnel garden is to make sure you have created a biodiverse and resilient ecosystem. A system that is in balance will have pests, of course. But the numbers of those pests will be kept down by predatory species that eat them.
The most important predators of cabbage white butterflies are garden birds. However, many other creatures prey on these butterflies (and their eggs, larvae and caterpillars) too. There is one parasitoid that attacks cabbage white caterpillars in the UK: parasitic wasps called Cotesia glomerate. Other insect species, spiders, amphibians, reptiles and certain mammals also help keep their numbers down. Sprays with bacillus thuringiensis, a bacterium naturally found in soil, can also help.
Encourage Cabbage Whites To Lay Eggs on Sacrificial Trap Crops
Rather than destroying the eggs, it could be a better policy to encourage the cabbage white butterflies to lay their eggs elsewhere. This might mean you draw them into another part of your garden, or it might mean simply adding trap crops that you will not mind the caterpillars eating. By placing sacrificial trap crops that cabbage white butterflies prefer relatively close to your brassica crops, you can encourage them to leave your more important and valuable crops alone.
Nasturtiums are one good trap crop to consider. They are not only a good trap crop for cabbage white butterflies, but also for flea beetles and a range of other common pests. Sea stock, Dame’s violet and Honesty are other plants that can be used in this way. And there are a range of other trap crops that can be considered.
Plant Companion Crops That Will Repel Cabbage White Butterflies
In addition to thinking about using planting to draw cabbage white butterflies elsewhere, you should also think about repelling them. There are a number of plants that are said to repel cabbage white butterflies. And many of these are effective – at least to a certain extent.
Plants that may help to repel cabbage white butterflies include:
The strong scent of many aromatic herbs can confuse or distract pests, masking the scent of brassicas so cabbage white butterflies are less likely to find them and lay their eggs on them.
Trick Cabbage White Butterflies By Placing Decoys in Your Polytunnel
Another thing that is said to keep cabbage whites away is decoys. Decoy butterflies are simply pieces of white plastic or white fabric that are cut into butterfly shapes and placed among your crops to make other cabbage white butterflies think that there is already a butterfly there.
I can’t personally speak as to the effectiveness of this technique, but if you have a problem with cabbage whites in your garden, it could be another option to try before you decide to resort to any more extreme measures of control.
Create Physical Barriers to Protect Your Crops
The only sure-fire way to keep crops safe from cabbage whites is to create a physical barrier between the butterflies and your brassica crops. Placing close nets, mesh or solid row covers over your brassicas will ensure that butterflies are not able to lay their eggs. So of course, it is the most effective way to keep brassicas safe from very hungry caterpillars.
You might not be keen to entirely cover your growing areas to keep your cabbages, kale, broccoli etc. safe. But if there are a lot of cabbage white butterflies in your area, this really is the best solution.
Be sure to not get confused between cabbage white butterflies and cabbage root flies, as the latter can pose different problems entirely.
FAQs
How rare is a cabbage white butterfly?
The cabbage white butterfly is not rare and is considered one of the most common butterflies in many parts of the world, particularly in North America and Europe.
What time of year do cabbage white butterflies lay eggs?
Cabbage white butterflies typically lay eggs in the spring and summer months when temperatures are warmer and food sources are plentiful for the larvae.
Do white butterflies eat cabbages?
Adult white butterflies do not eat cabbages; they primarily feed on nectar. However, their larvae, known as caterpillars, do feed on cabbage leaves and can cause significant damage to the plants.
Sources
Peerless, V., (2021) How to grow and care for nasturtiums. Gardener’s World. [online] Available at: https://www.gardenersworld.com/how-to/grow-plants/how-to-grow-nasturtiums [accessed 20/09/24]
