Be Cabbage White Butterfly Free!

homegrown organic broccoli ediblebackyard nz

This summer, for the first time ever, I grew brassicas out in the open without any insect mesh. From seedling to finish. I was feeling confident in my parasitic wasp population, and they didn’t disappoint.

What a turn around! For most of my garden life I haven’t bothered growing brassica through summer because the cabbage white caterpillars decimated them. However, gardens – along with life – are ever changing.

Over 12 years gardening here, the beneficial insect population – seduced in by my perennial companions and spray free ways – has grown and diversified. The flow on effect of all those predatory + parasitic insects is there’s alot less pest management for me to do. Less psyllids, less aphids, and this last improvement – a gang of parasitic wasps who happen to live off caterpillars.

So while I’m not cabbage white butterfly free, they’re still flapping about out there – I am, at the moment, free from managing them. Notice the flexible statement. Lets not ever set anything down in stone – its all evolving, remember.

4 ways to cabbage white freedom

Call in the beneficial insects

paper wasp eating a cabbage white caterpillar
Paper wasp munching a cabbage white caterpillar.

Beneficial insects are your long term, pest control strategy. As far as the cabbage white butterfly goes, there are three wasps I know of that come out to play.

  • Braconid and pteromalid parasitic wasps use caterpillars as a mobile nursery. They lay their eggs in or on them, providing a delicious first meal of caterpillar for the youngsters upon hatching.
  • Paper wasps kill and chew caterpillars, and bring them back to the nest to feed the young.

Some of you, I know, will be worried for the monarchs, but I prefer not to get too involved here, and leave the balance of these things to nature. I still have butterflies.

The way to a booming beneficial insect population is to feed and house them. Plant loads of perennial companions in order to provide a year round supply of nectar and pollen. Spray no nasty chemicals – benies are more sensitive to herbicides and pesticides than pests are. Create densely planted areas for habitat. And let pest populations go for as long as you can bear – those pests are calling in the predators after all.

While you build your beneficial insect population, manage the cabbage whites by squashing caterpillars, flicking off eggs and/or covering the crop.

Squash the caterpillars

Focus on young seedlings. Remember to check your seedling trays too. Hungry caterpillars sure can eat and make short work of small plants. Squash any you find. Check under leaves for the creamy, bullet shaped eggs and flick them off.

Cover the crop

February planted brassicas under insect mesh

Insect Mesh is a god send. It keeps the butterfly from laying eggs, there by preventing the caterpillars in the first place. Do keep your eye on the seedlings though, incase any eggs were laid before the cover went on.

Spray

dead caterpillar
A dead tomato looper caterpillar, after BT spray.

Spraying is for the busy person who doesn’t have time to squash caterpillars or has no insect mesh available.

BT (Bacillus Thuringiensis) is the active ingredient in Kiwicare’s Organic Caterpillar Control, and Yates Natures Way Caterpillar Killer. For bigger gardens you’ll need more than these small packs. Farmlands sell a commercial pack of Dipel. Costs a bit so maybe a good idea to go splits in your co-op/ garden group/ neighbourhood.

Mix it up and spray it all over your brassicas fortnightly to keep up with the egg hatchings. BT only impacts those that eat the leaves which is what makes it safe for bees, ladybugs and all our other friends. The potential is, it will kill any caterpillar that munches the sprayed foliage, so bear this in mind.

Keep this job on your radar until the heat subsides and the cabbage whites disappear late autumn.


Derris dust alert!

Let’s stop with the Derris Dust. I know its easy. I know Grandma used it. But it’s super toxic! Rotenone, the active ingredient in Derris dust is a neurotoxin and fatal to many of our important beneficial insects – parasitic wasps, ladybirds and dragonflies to name a few. Canada has outlawed the use of it on gardens and looks like USA is going the same way.

Comments

  1. Great news Kath, we’re just over the Ohau river and we’ve also had a good broccoli summer with a 5th way. My study window overlooks the veggie patch. As soon as I see a cabbage white butterfly I run outside and whack it with a fly swat before they lay their eggs. No chemicals. Now I just need to catch the scwewy wabbits.

  2. I just got a tip from my local garden centre to add a bit of lime into the planting hole. They plant will take some of it up and apparently the caterpillars can’t deal with it.
    I haven’t tried it (in fact I forgot to add the lime while I planted them out last week, so may need to replant them this weekend), but wanted to share the tip anyway!

    • Interesting Helga! Thanks for sharing – it’d be great to try it and see what happens. I’m not sure about the lime in the bottom of the hole though – thats my gut feeling. Endless experiments in the garden 🙂

  3. Planted celery amongst my brassica and have had garden any problems with caterpillars, seems they don’t like the smell. I’m sold on it anyway.

  4. I flick the white butterfly eggs off the leaves, but I worry – could the eggs still hatch lying on the ground under the plant and then climb back up and start munching?

  5. Hi Kath – Here in Melbourne (Victoria, Australia), we have loads of white butterflies, more than I have ever seen in my garden. I catch them mid air with a tennis racket and feed them to my chooks. They come running for them. I also pick off the caterpillar’s, put them in a shallow tin lid and give them to my chooks. They love all these natural treats and produce extra yellow eggs for me. A win win situation.

  6. Always interested to read about what might work with the dreaded white butterflies. I’m still resigned to insect netting since it does work, except for the most cunning! I am interested to know your suggestions for codlin moth. Have read about pheromone rings, want to test Neem granules this year to see if they might work. Will search to see if you’ve advised on this previously.

  7. Would water get to the plants using a net like in your picture ? I am told old net curtains work but then someone else says that water/rain doesnt get to the plants.

  8. No problem with rain or hose water getting through insect netting.

  9. Hi Kath, myself and friends have noticed a near absence of white butterflies throughout Nelson so far this year. We wondered if paper wasps are eating them or some new predator. Usually we all have to manage carefully. Any knowledge on this? It’s definitely not just because our gardens are improving

    • Nice! Something is managing the cabbage whites and its most likely at the caterpillar stage… so probs a predatory wasp. Take a suiet sit in your garden – brassicas are a good spot for this and park up and see whats going on. I’m sure your gardens are improving, by the way!