Cabbage white butterflies may look pretty, but their caterpillars can quickly destroy garden crops.
Though we should welcome wildlife in our gardens, it is important for those who are growing their own to be aware of this common pest, and the problems they can bring, especially for brassicas.
Members of the cabbage family can be eaten rapidly if you get an infestation of cabbage white caterpillars. But there are a few things you can do to keep your plants safe.
The strategies for dealing with cabbage white butterflies in organic gardens revolves around a few simple things:
- Companion planting (which can confuse, distract or repel this species, at least to a degree)
- Attracting predators which prey on cabbage white butterflies and their caterpillars.
- Making the area a less appealing place for cabbage white butterflies to lay eggs. (By making them think the area is already occupied by other cabbage white butterflies, for example.)
- Creating physical barriers over your plants.
The first two strategies can work to a degree. It is important to maintain a natural balance in the garden ecosystem so that all pest species are kept in check.
But no matter how vigilant you are, the only sure-fire way to stop cabbage white butterflies from laying their eggs and caterpillars from destroying your plants is to keep them covered, and to form a physical barrier that these pests cannot breach.
Companion Planting For Brassicas to Tackle the Problem
Choosing the right companion plants to grow alongside brassicas involves thinking about plants that will disguise the scent of the brassicas and make it less likely that these butterflies will find them and lay eggs on them.
Many aromatic herbs have strong fragrance and when planted alongside brassicas as companion crops, can make it more difficult for cabbage whites to find.
Cabbage whites may also be repelled to a degree by these strong-smelling plants.
Remember, companion planting is also key to attracting beneficial wildlife. The plants in any garden should be chosen to encourage a wide range of beneficial creatures to the space.
Distracting Cabbage White Butterflies with Trap Crops
It is also a good idea to think not just about companion plants for brassicas, but also plants to place elsewhere in your garden which attract cabbage whites and act as sacrificial trap crops.
By planting trap crops elsewhere in your garden, you can lure cabbage whites away from plants which you are particularly keen to protect.
Remember, cabbage white butterflies are important elements in the ecology of your garden. So you should not ever aim to eliminate them, but rather to protect the plants you wish to protect while offering them a home elsewhere in your garden.
Nasturtiums, for instance, are one example of a trap crop. They will attract cabbage white butterflies, as well as several other common garden pests, which will often be attracted preferentially to feed on these rather than on more prized crops and garden plants.
Sea stock, honesty plant, and Dame’s violet are three other attractant plants for cabbage white butterflies to consider.
When these are placed in your garden, the butterflies may lay eggs on these rather than on your brassicas. Then when the caterpillars emerge, they will eat on the plants where they find themselves rather than gorging on your cabbage family plants.
Attracting Beneficial Wildlife to Keep the Garden Ecosystem in Balance
Remember, the plants you choose for your garden and the habitats you create are key to pest control in an organic garden.
Garden birds are very welcome if you want to stop cabbage white butterflies destroying your plants. Many garden birds are important predators of these pests.
Attracting garden birds can be one way to keep pest numbers down. You should also be sure to welcome and attract other insect species (such as parasitic wasps, Cotesia glomerate), spiders, amphibians, reptiles and a number of mammals to your garden as these will also prey on cabbage white butterflies and their caterpillars and help keep their numbers down.
Making sure that garden soil is rich in beneficial soil life, including the bacterium bacillus thuringiensis, is also key. This bacteria also helps keep cabbage white numbers down – and can be purchased as a spray solution in extreme cases.
It is also worth mentioning that domestic chickens can also eat caterpillars and help keep their numbers down.
Just don’t give chickens access to your cabbages and vegetable plots – as chickens too will quickly eat the lot if given the opportunity! Instead, consider placing trap crops (as mentioned above) in an area where chickens forage.
While we are not entirely convinced by the efficacy of this strategy, some gardeners swear that you can keep your plants safe from cabbage whites by adding decoy butterflies.
These decoy butterflies, it is said, make it less likely that cabbage white butterflies will lay eggs close by as they believe that the area is already occupied.
People make pretend cabbage white butterflies out of white paper, white fabric or white plastic (cut from old milk containers, for example). Place these among their brassica crops.
While this strategy may or may not work, it could certainly be worth considering before you adopt more extreme solutions.
Even when you adopt some or all of the strategies above, the only way to be absolutely certain that you won’t lose your brassica crop to cabbage white butterflies is to place physical barriers over the crop.
Place a fine netting, mesh or other fabric row coverings over any cabbage family plants to keep them safe from hungry caterpillars.
Though this may not be the most attractive feature in your garden, this is certainly the only way to avoid any losses at all when growing brassicas in your vegetable plot.
Make sure you place the barriers as soon as you see cabbage white butterflies flying around in your garden (and ideally before). Observation is key and you will need to keep a close eye on your brassicas and look under leaves to make sure no eggs have already been laid.
Physical barriers will only work if you place them before eggs have been laid. Otherwise, caterpillars will munch away under the covers and you could lose the lot!
If you think you may have been a little late in placing your barriers, you may have to check over your plants carefully and remove by hand any eggs which have already been laid.
Remember, both types of cabbage white butterfly present in the UK, Pieris brassicae (the large white) and Pieris rapae (the small white) lay eggs that become voracious caterpillars.
But both can also be beneficial in your garden. So do not get try to get rid of them altogether – cover your key crops, and plant wisely so you can live and let live.
As a horticultural therapist, professional gardener and freelance writer, Ed is passionate about the healing properties and processes of gardening and nature. With a background in occupational therapy, Ed now runs a community garden where he aims to encourage and enable the local community to grow fruit, vegetables and cut flowers and experience the many benefits of gardening. Ed lives in West Sussex with his young family and golden retriever, where they look to live the good life by growing as much of their food as possible. See Ed's website here.