Land Cress as a Cabage White Butterfly Dead End Trap Crop

Land Cress (Barbarea vulgaris) is also known as Upland Cress, American cress, Rocketcress,  Bittercress,Yellow Rocket, and has a few other common names.  Common names can be deceptive, for example a sea horse is not related to a horse and a sea cucumber is an animal and not even a plant, so always try to go by the binomial name when buying plants to ensure you get what you want.

Cabbage White Butterfly is a major pest of brassicas in Australia and many other countries.  They quickly decimate brassica crops and controlling them organically can be problematic.  There are a lot of superstitious myths about controlling them which do not work, as well as a few techniques that help quite a lot.

We have controlled cabbage white butterfly in the past by using white strips of plastic (cut from a white plastic bag), tied in the middle to a piece of string, so it looks like a lot of white butterflies are flapping around.  This results in less butterflies laying eggs on your plants, apparently the butterflies do not want to lay where there are heaps of other butterflies to help ensure their young will have enough food.  It does not completely eradicate the pest, but it lowers the numbers to a level where they can be picked off by hand each day.  This has worked well for me many times in the past.  This is a lot of work unless it is a very small area, and if you fall ill a day or two the caterpillars sometimes eat out your crop, surely there is a better way!

I have heard people claim that egg shells will deter cabbage white butterflies as they also think it is other butterflies.  I have tried this several times and had no noticeable difference.  Not only has this never worked for me, but birds tend to steal the egg shells.  Before you ask, no, the birds did not make any noticeable effect on the butterfly population but they often caused damage in the garden.  This appears to be one of those superstitious garden myths that fill gardening books, are spouted by people who should know better, and actually prevent people from growing food organically.

Many people claim that Upland Cress can be used as a dead end trap crop for cabbage white butterfly.  They claim that the butterflies are attracted to land cress, they lay the eggs there instead of on other brassica crops.  Once the eggs hatch the young caterpillars are meant to bite the leaf and some toxin kills them, other places claim that the caterpillars can't eat the upland cress so they die.  The information varies between sources, but the cabbage white butterfly caterpillars are not meant to survive and grow to be able to complete their life cycle.

This sounds like a perfect solution to cabbage white butterflies.  I was extremely excited when I first heard about this.  I did some research so ensure that it was Barbarea vulgaris that was referred to and not some other plant with the common name of 'land cress'.

I bought some Barbarea vulgaris seeds and planted them near some other brassicas.  I have done this twice now with the same result.

I wanted to see if Barbarea vulgaris:
1) prevented cabbage white butterflies from laying eggs on other brassica plants
2) killed the young caterpillars
3) prevented the caterpillars from completing their lifecycle.

Achieving any of these things would be fantastic as it means that upland cress could be used as a way to reduce cabbage white butterfly damage.  I will break down my experience under similar headings so other you can learn from my mistakes.

1) Does Upland cress prevent cabbage white butterflies laying eggs on other crops.
No.  My upland cress certainly attracts the butterflies and they lay eggs on it.  Unfortunately they also lay eggs on all the other brassicas in my garden apart from water cress (which was somewhat protected).  If the upland cress kills the young caterpillars it could be used to lower the numbers of cabbage white butterflies and be of some benefit.

Land cress with cabbage white butterfly larvae and frass

2) Does Upland Cress kill Cabbage White Butterfly Caterpillars when they feed on it?
No.  The eggs hatch and the caterpillars happily eat it to the ground leaving nothing but tiny stems.  The picture above shows some growing and it has third instar caterpillars on it.  This means that they not only can survive on upland cress, they can grow on it too.  Perhaps they will eat out the cress but some chemical in its leaves will prevent them from completing their lifecycle.  I decided to leave some caterpillars to see what would happen.

3) Does Upland cress prevent cabbage white butterfly from completing its lifecycle?
No.  The caterpillars grow and pupate into butterflies, thus completing the lifecycle and rendering upland cress useless as a bio-control for cabbage white butterfly.


Upland Cress does not control cabbage white butterfly

Clearly Upland cress does NOT kill cabbage white butterfly larvae and can not be used as an effective means of controlling this pest.  I had such high hopes that this would be used as a way of at least lowering the number of cabbage white butterflies or lessening their damage.  I guess I could grow upland cress and pick off the caterpillars, but I could grow any brassica and do the same so upland cress provides no benefit here whatsoever.  I am very disappointed by this result.

Some very reputable sources claim that Barbarea vulgaris works as a dead end trap for cabbage white butterfly, but as I have demonstrated clearly it doesn't work under all situations.  Thanks for nothing Gardening Australia and Jerry Colby Williams!  Thanks for nothing seed sellers who have a vested interest.  They should know better and stop spreading this nonsense.  This is one of the reasons why I try not to read organic gardening books or magazines, they are often filled with inaccuracies such as this that cause far more harm than good.

Upland cress is useless against cabbage white butterfly

Apparently there is research that suggests that Upland Cress (Barbarea vulgaris) does control cabbage white butterfly under certain situations.  I have not read this research myself so don't know under what specific circumstances it has worked.  Unfortunately it does not work in my garden, so there is more to it than simply growing upland cress to control these butterflies.  Perhaps there is some predator or some disease or something else that is at work that is simply not present in my garden.

Regardless, upland cress does not control cabbage white butterflies in my garden and there is no guarantee it will be any different in yours.