A few weeks ago I was feeling pretty good about my brassicas and their infiltration (or lack thereof) by the cabbage moth (also known as the cabbage butterfly or pieris rapae) . I’d seen a few flitting around the garden, but hadn’t spotted any landing on my plants, and I thought that my companion planting with onions had done the trick.
Even during the heat wave I didn’t really notice anything wrong, and thought that they were going marvelously, given the temperatures.
That was last week.
This week I got out of my car and wandered past the vegie patch. And wondered what on earth was going on with the horribly decimated plants that were hanging out there.
My first thought was snails (those pesky beasts) but I haven’t really seen many around the garden lately, and it certainly hasn’t been wet enough for them to be out in their droves.
So I got closer. And found the culprit.
My first thought was something along the line of “ewww gross” and my second was “how do I get rid of cabbage moth caterpillars?”.
Turns out someone else in the garden was working on the answer to that question for me.
The elusive ladybug. I never see hide nor hair of them when my roses are covered in aphids, but apparently they are quite happy to dine on cabbage moth eggs.
Google informs me that they predate on cabbage moth eggs, but it doesn’t tell me how effective they are. With that in mind I took to chopping off the leaves which seemed most covered by eggs (but I left some for the ladybugs to dine on. I’m not sure if I’m going to regret that or not).
I also went in search of the caterpillars. They’re simultaneously really tricky and really easy to spot. A cursory glance won’t reveal them, but once you know what you’re looking for they seem to be everywhere! I think I killed (or picked off and threw away) about 30 caterpillars. I’m hoping that when I go out and check on the plants tomorrow there aren’t more of them.
Once eggs and caterpillars have struck there’s a limited number of things you can do: you can try removing the eggs/caterpillars by hand and destroying them, encouraging natural predators (such as birds and ladybugs), spraying with a sour milk or garlic solution or spraying with a commercial spray that contains Bacillus thuringiensis (BT). This is supposed to target only caterpillars, and be safe for other insects (like bees and ladybugs).
Alternatively you can try preventing the moths from landing and laying in the first place. There’s a few ways to do this: catch and destroy any cabbage moths in the garden, establishing an insect-proof netting around plants (though this may also stop beneficial insects), spacing out plantings to make it harder for the cabbage moth to identify and land on the brassicas. Some people also plant ‘sacrificial’ plants, like nasturtiums, which also attract the cabbage moth. They let them land on/lay on this plant in order to keep them off their brassicas.
On the plus side I’m not planning on eating the brassica leaves so it’s not as though the plants are doomed, but I suspect they might need a fair few number of leaves for that whole photosynthesis thing…
Have you been affected by the cabbage moth? How do you deal with it?