As I mentioned in our recent newsletter, this autumn I’ve noticed a lot more White Cabbage Butterfly (Pieris rapae) in our gardens than usual. White Cabbage Butterfly lay their eggs on our Brassicas, such as broccoli and cauliflower. Little green caterpillars hatch from these eggs, and then get to work chewing holes through the plants.
A few holes in the leaves is not a major concern for your Brassicas. However, the numbers of caterpillars this year, have left some of my plants stripped back to bare stems. There are several methods you can use to control White Cabbage Butterfly, as well as other caterpillars.
White Cabbage Butterfly or White Cabbage Moth?
Pieris rapae, the flying insect whose larvae eat your Brassica leaves is a butterfly, not a moth. So it is the White Cabbage Butterfly, not the White Cabbage Moth!
Decoy Plants for White Cabbage Butterfly
Since we have moved house, we haven’t planted Nasturtiums in our garden. This could be one of the reasons why we are having such a caterpillar problem in our garden. White Cabbage Butterfly love Nasturtiums, and will often seek these plants out to lay their eggs on, instead of the Brassicas.
Using Dipel to Control White Cabbage Butterfly
If things get really desperate you can spray your plants with Dipel. This biological control is a bacterial stomach poison for all caterpillars, which is mixed with water and sprayed onto both sides of foliage. It must be ingested by the actively feeding caterpillar, which will then die 3-4 days later. It is not a contact spray. It is considered safe for beneficial insects, including ladybirds and bees as well as fish, birds, mammals and pets. Dipel contains Bacillus thuringiensis (Bt), which is a bacterial toxin and specific against most species of leaf eating caterpillars. Dipel is listed as an organic spray.
Search and Destroy Missions for White Cabbage Butterfly
The easiest method to control caterpillars is via search and destroy missions. It’s a great activity for the kids to hunt them down. You can then squish them, or feed them to the chooks. It can become quite a game of hide and seek, as most of these caterpillars are masters of disguise. Make sure you inspect the undersides of leaves, as that’s where a lot of them hide during the day.
Allowing Parasitic Wasps to control White Cabbage Butterfly
This year, rather than squishing them all, I’ve been trying to relocate the cabbage moth to other plants that are less important to us. The idea is that by maintaining an abundance of these pests in the garden, predatory wasps will be encouraged to breed up and tackle the problem for me. This method was semi-successful, as I have noticed an increase in number of Predatory Wasps in the garden. Predatory Wasps inject their eggs under the caterpillar’s skin. Then their larvae hatch and consume the caterpillar from the inside out, eventually killing the caterpillar.
Here’s a video that I recorded a few weeks ago. It shows Parasitic Wasps hatching out of a Dainty Swallowtail Chrysalis.
Decoys for White Cabbage Butterfly
You can also try tricking the White Cabbage Butterfly with decoys such as fake moths and even eggshells! The theory is that using these decoys tricks the White Cabbage Moths into thinking the leaves are already home to caterpillars and are too much competition for more eggs. In reality, decoys don’t work and your precious broccoli will still be marauded by little green caterpillars.
You can also use a fine netting to keep the moths from laying eggs on the plants. You will need to put the netting over as soon as you plant the seedlings. If you wait until there are signs of caterpillar damage, it is too late, as you just trap the emerging moths inside the netting. Which means they have to lay eggs on the plants inside it.
Or, Just Wait for the Cold Weather!
As the weather turns colder, pest species such as Aphids, Whitefly and White Cabbage Butterfly will become less of a problem. So try and avoid using sprays in the garden, if you can, and let nature take care of it for you.
Our white cabbage butterfly problem was eventually cleaned up by another much despised pest in Melbourne.
Do you have any tried and tested methods for controlling White Cabbage Butterfly? Please share your experiences with us in the comments section!
Want to know more about garden pests?
The idea of a relaxed approach to pest control will appeal to many of you. We have put together a three part blog post series on pests, predators and effective control methods.
If you would like further information on garden pests, then please sign up to our Science of Edible Gardening Workshop Series. The April workshop (repeated annually) in the series focuses heavily on population dynamics and controlling garden pests.