Beating the Cabbage White Butterfly

Beating the Cabbage White Butterfly

I have been seeing lots of posts around Facebook over the last few months with gardeners having issues with Cabbage White Butterflies (Pieris rapae). Lots of well-meaning people are advising that the offending pest is the Cabbage MOTH – however, that is a completely different creature.

Firstly, a big part of protecting your garden is “Know thy enemy”, so let’s take a closer look at the CWB (Cabbage White Butterfly abbreviation). It is mostly active during the warmer months and will target your vegetables in the brassicaceae family such as broccoli, cabbage, cauliflower and bok choy. It can be heartbreaking to watch healthy seedlings that you have babied through their early stages being decimated before your very eyes. 

1. ADULT – The male is identified as having two black spots (one on the forewing and one on the hindwing) and the female has three spots (two on the forewing and one on the hindwing). Adults live for up to 3 weeks. 

2. EGGS – Eggs are tiny, yellow, upright eggs usually singularly laid on the underside of the leaf. The egg stage lasts for only 1 to 3 days. 

3. CATERPILLAR – The caterpillar is green with a velvety look due to tiny hairs covering the body and has a faint yellow stripe down the back. The caterpillar stage lasts from 10 to 15 days. 

4. PUPA – The pupa is angular and quite attractive. It can range from green to brown in colour and will changed depending on the background of where it is anchored. The caterpillar will often crawl away from the host plant to pupate. This stage lasts for about 8 days.

 

 

Some of the tips floating around Facebook for ridding yourself of these garden pests are:

  1. Net everything! Ok maybe, but I live on an acreage where my plants are all just tossed in somewhere amongst the rest of my gardens or food forest area. Not only is it impossible for me to net my brassicas, I hate to exclude the birds, lizards, wasps and spiders which are my best friend when it comes to dealing with my pest issues. And of course no one wants to exclude the pollinators. So this option is out for me.

  2. Put fake butterflies around the garden (or plant white flowers). They say that the CWB is territorial and will not lay eggs where another is already active. I am not sure how correct this is because I sometimes see two working away very near to each other. I have tried this option but still found eggs right next to my decoy butterfly. I am not ready to rule it out completely as maybe it will lessen the attack – but it certainly didn’t prevent it in my case. I have looked for scientific evidence for this method but have found none. Try it and let me know your results. You need about 4 or 5 per square meter to be effective (apparently).

  3. Pesticides. I don’t like using any pesticides. Many are indiscriminate and will kill your good bugs as well as your bad. Your pests are also the food source for your good guys so I don’t mind having a few around to feed them anyway. Diatomaceous Earth is often mentioned. This is a naturally occurring sedimentary rock derived from fossils; it breaks down the waxy coating on soft-bodied insects such as caterpillars and causes them to dehydrate. As good as this sounds, due to the fact that it comes from the fossilized remains of an ancient algae up to 65 million year old, I don’t consider this a sustainable resource.

  4. Trap crops. Cress is a trap crop for both Cabbage White Butterfly and Cabbage Moth. This means that they will lay their egg on the cress rather than your brassicas. You will hear people say that the hatched caterpillar will die when they eat the cress however, this is only true for the Cabbage Moth – cress does not kill the caterpillar of the Cabbage White Butterfly.

  5. Hand removal. Of course this will always work but is extremely labour intensive and therefore likely to not be sustained long term. There will always be caterpillars you miss and what happens if you want to go away on a holiday?

  6. Dipel. This is a natural bacteria that targets the caterpillars of butterflies and moths which die after they ingest the product. While this is something I would be open to using I am concerned about the embodied energy when it comes to production and transport of Dipel. Also, no one knows the effect on my existing soil microbes when exposed to large quantities of the bacteria used – does it upset the natural balance? Also, many of the moths and butterflies in my garden are my friend and I don’t want to target them all indiscriminately.

So now I have a big and very confronting question I want to ask you: “Who do you think you are that you believe you have the right to play God and remove an entire species from your local ecological web simply because you want to eat broccoli!?”. As permaculturists we are taught to work WITH nature – not try to concur her. By removing an entire species from our garden food web we create a ripple effect that destroys the other species in that web which rely on the one you have removed.

Now when it comes to the CWB’s in my garden it is all about controlling the attack until Mother Nature steps in to do the work for me. Firstly, the CWB is most active in the warmer months and although they can also be active during winter the pressure is reduced. You can try to plant late in the season to avoid the worst of the breeding season. By planting late in the season you reduce the window when the weather is still warm and the CWB’s are most active. Due to this shortened growing timeframe choose fast maturing or “cut and come again” type brassicas wherever possible.

READ ON TO LEARN MY TECHNIQUE TO DEAL WITH CABBAGE WHITE BUTTERFLIES…

Prepare to have your mind blown! I let nature control the CWB’s for me!

  1. Spread your brassica plants throughout the other plants in your garden. Don’t put them all together in the one bed as this is like laying out a buffet for the pests that target that a particular plant, making it easy for them to find your crop and move from one plant to the next.

  2. Grow plants nearby that attract the predators to your garden. Parasitic wasps love to feed from tiny flowers and can be attracted by planting plants from the Apiaceae family. This plant family is recognisable by their umbrella shaped flower clusters – such as parsley, dill, fennel, yarrow, carrots, coriander, etc. Spiky dense shrubs are also great for attracting small insectivorous birds. And don’t forget also to provide a water source for both birds and insects.

  3. Keep your plants healthy! Pests will usually target the weakest plant in your garden so to minimise this do everything you can to keep your plants as healthy as they can be. Just as the wolf is nature’s way of weeding out the old, sick and weak from the animal food chain – pests and disease is nature’s way of weeding out the sick and the weak from the plant world, so LET IT HAPPEN so only the strong and healthy survive to produce seed for the next generation. And don’t forget that healthy soil full of life is what keeps your plants healthy – add compost, organic fertiliser, water, mulch, love….

  4. Now, here is where things really start to get interesting! Wait until you start getting attacked before you take action. Sounds counter-intuitive, but wait! Work out which brassica is the first/worst affected and then LEAVE THIS PLANT AS A SACRIFICE FOR THE CWB’S! They will favour this one as “sickly” and reduce the attack on the other plants. No need to grow cress or research what plant is a trap crop for the particular vegetable you are growing as you already have the answer right there in front of you – it is the plant itself! This plant will become infested with CWB caterpillars but DO NOT be tempted to remove them. The caterpillar needs to reach a certain size before it is large enough for the parasitic wasp to lay her eggs inside them. And THAT will be your main ally! The parasitic wasp known as Cotesia Glomerata will lay her eggs inside the caterpillar and the caterpillar will die when they hatch. Other predators such as small birds will also move in to feast on the caterpillars on your sacrificial plant and will deal with anything on your other plants while they are there. And if you save your own seeds, this also helps you to automatically select the seeds from the plants which may be more resistant to pest attack and therefore improving on the genetics year after year. It has a name – natural selection!

  5. Remove the leaves of any other brassicas which are touching your sacrificial plant. Hopefully you shouldn’t have any if you have spread your plants throughout your garden, but I sometimes plant by tossing seeds everywhere and can get two of the same type of plant growing side by side.

  6. On all of the plants that you want to save/protect, as they grow remove all lower leaves – don’t waste them, eat them or feed them to your chooks. Do not remove the top leaves at the growing tip. You can choose to not remove the leaves closest to the ground if you like as the CWB prefers to lay eggs on the underside of the leaves so these ones where she cannot get underneath will not be targeted. However, if you DO remove the leaves close to the ground you gain extra planting space as you can plant smaller vegetables underneath the brassicas where it would have otherwise been shaded!  You have now increased your harvest – both by eating the leaves removed from the brassica as well as planting a second crop below. Bonus!!

  7. Check your plant leaves regularly and remove any eggs or caterpillars you see on your crop plants (but leave them on your sacrificial plant). This job now takes no time at all as you have cut your workload down by about 80% by removing most of the leaves! The eggs will mostly (but not always) be attached to the underside of the leaves. And keep an eye out for the first tell-tale signs of a caterpillar. It will start as a tiny pinprick hole – look on the underside of the leaf and you will usually find a very tiny, almost invisible, but very hungry green caterpillar.

  8. For some brassicas which form a head (such as broccoli and cauliflower), once the head forms you can bag this with a mesh bag – just like you see done for fruit on fruit trees. Keep any caterpillars off the head of broccoli while leaving the rest of the plant to host any caterpillars. Most people don’t eat the leaves anyway! Make sure the bag has a good seal where it attaches around the stem.

After 34 days I saw the first signs that the cavalry had arrived! As expected, the green caterpillars of the CWB left my sacrificial broccoli positively skeletal! Almost nothing was left but the veins of the leaves.

It takes a little time for the activity of the caterpillars to attracted the parasitic Cotesia wasp. She is attracted to the chewing of the CWB larvae and when she arrives will lays her eggs inside the caterpillars (they need to be large enough to support her young first though). After laying her eggs inside the caterpillar the eggs hatch and the larvae live inside the body of the caterpillar and eat away at its insides while leaving the vital organs untouched so the caterpillar continues to survive. Gruesome, I know. It takes 15 to 20 days for the larvae to emerge, killing the parasitised caterpillar in the process. The newly emerged larvae then spin cocoons in a cluster on or nearby the host caterpillar, hatching after 7 to 10 days to provide you with the next generation of wasps to protect your garden.

 

After about 6 weeks I still had plenty of caterpillars to support my growing population of wasps, but an astounding thing happened – I found that there were fewer and fewer eggs and young caterpillars appearing on my plants. At first I put this down to the cooling weather until I noticed plenty of CWB’s still flitting around in the paddock next door. I then watched in amazement as a CWB flew past my garden with the broccoli in it and totally ignored my plants!! It appears that the CWB’s can detect that my little patch of garden is protected by a healthy wasp population. After about 2 months I no longer saw any eggs on my brassica plants and stopped checking them all together.

6 weeks after my CWB problem completely disappeared and I had stopped bothering to check for eggs and caterpillars I happened to find 5 caterpillars on my brassica plants. I took these and moved them onto my sacrificial broccoli (which, interestingly, is now the biggest in my entire patch). Aside from these random 5 caterpillars I have not seen any more CWB caterpillars on my brassica plants. It has now been 5 months since I first started my experiment and it seems my plants are still under the protection of my local parasitic wasp population.

My sacrificial broccoli plant was key to this strategy. I provided a breeding haven for the parasitic Cotesia wasp – a service I could not have provided had I chosen to net, spray, and kill all of the caterpillars. I would rather support my beneficial insects and let them help me protect the rest of my brassica plants.

On a final note, my sacrificial broccoli plant has exploded back to life with regrowth everywhere. I still have never removed a single egg or caterpillar from this plant but it is covered in leaves that my local CWB’s are too scared to go near!

Nature knows best!

Now run outside and create your oasis!

Jo