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Want to get ahead of pests which devour cabbage, broccoli, kale, and other brassicas? Avoid a “brassica massacre!” Here are natural, no-chemical ways to avoid cabbage worms, loopers, aphids, and other soft-bodied insects so that you, too, can enjoy healthy harvests of these must-grow veggies!
The Worse Brassica Pests
If you’ve arrived on this page, you probably already have a pest in mind that you want to tackle. We’ll cover the most common pests that eat up your brassicas. This family includes: broccoli, Brussels sprouts, cabbage, cauliflower, collards, kale, and kohlrabi. (See our Growing Guide Library for planting and growing information for each of these vegetables.)
Generally, there are two pests that bother brassicas more than any other: caterpillars and birds.
Cabbage worms: It’s early summer and, in my neck of the woods, this is the time when butterflies such as the cabbage white, and moths like the diamondback moth come out to play, ready to wreak their worst! Their caterpillars, also known as cabbageworms, devour young plants, eat holes in leaves and can ultimately strip leaves down to their midribs, leaving plants skeletal shadows of their former selves. In warmer climates, the damage can start much sooner in the season. Your job, as gardener, is to catch them long before they cause such damage, ideally blocking them altogether.
Birds: As we move into winter and then on into spring it’s the turn of birds. In my more urban area, it’s pigeons! With less to eat in the wider countryside, these hungry birds with their hearty appetites turn to our gardens. Here they’ll make short work of brassicas, tearing at the leaves as they feed to leave them ragged and bare.
Other common pests we’ll be dealing with today include cabbage aphids and whitefly, which take to the air in clouds when disturbed. Many of these bugs will hide on the undersides of leaves, so when looking for them, be sure to thoroughly check plants all over – top and bottom!
Watch this video to learn more about the natural pest control steps outlined below!
Step 1: Reduce Pest Risk
Prevention is better than cure, and we can employ tactics to keep these pests from ever bothering our brassicas in the first place.
Firstly, we can plant flowers that are known to confuse or repel pests – generally because of their strong scent. These include aromatic herbs and flowers, such as marigold, hyssop, mint, and thyme. Each of these has, to some degree, the ability to confuse or ward off pests, including aphids, mites, and cabbage moths.
Combine these plants with flowers known to attract pest predators, including predators of cabbageworms like tiny parasitic wasps. Many of these predators are drawn to simple, smaller flowers, including many flowering herbs: parsley, dill, basil and cilantro or coriander are great examples to plant around the garden bed. Just be aware that these need to be in flower early enough to attract the predators, so that may meen starting herbs off indoors to have at-the-ready to plant out.
Confusing pests is a superb tactic to deploy. For example instead of growing one crop at any single time or in any one spot, mix up crop families. This makes targeting specific plants, such as brassicas, a little harder for would-be pests, because what they’re faced with is a tapestry of plants, intricately woven together. And this principle applies to other crops too of course, for example carrot flies will find it harder to locate carrots and so on.
Be sure to remove brassica weeds from around your vegetable garden, as these might serve as a host for these pests, giving them refuge in between crops. Examples of brassica weeds: wild rocket/arugula, stray rapeseed/canola oil plants, mustards, hairy bittercress and shepherd’s purse.
Use bird feeders to attract insect-eating birds to your garden. Through regular feeding you’ll have them coming back for more – and it won’t just be the bird feed they’ll be eating – they’ll be on the lookout for tasty morsels down here in the veg garden too!
Cabbage root maggots, also known as cabbage root fly, can feed on the roots of brassicas, causing plants to wilt. You can protect plants by cutting a round of cardboard, cloth or heavy paper, then cutting a slit to the middle, and then installing this as a skirt around the plant’s main stem. Or you can buy purpose-sold cabbage collars. This simple method protects seedlings from egg laying by adult cabbage flies.
Step 2: Seek and Destroy
But what if your plants do happen to get infested with caterpillars or aphids? Well, if you are checking plants regularly and spot an infestation early enough, you stand a fair chance of stopping it before it gets out of hand.
You can cut off the worst-affected leaves and just ditch these onto the compost heap.
The natural presence of predators like ladybugs or ladybirds should help to keep populations to a manageable level throughout the growing season.
If you’re growing only a few plants, it shouldn’t be too much to pick caterpillars off by hand. Do with them what you will: feed them to your chickens, dispose of them in a bucket of water or, if you can bear to do so, squish them.
Some gardeners plant nasturtiums close to their brassicas to serve as a sacrificial or trap crop – basically a plant grown with the specific intention of luring a pest away from the crop you want to grow to eat. Nasturtiums, with their soft, fleshy leaves, are a cabbageworm’s favorite! Another great sacrificial crop are collards.
Once they become infested you’re best then digging them up and destroying the plants, taking the caterpillars with them, perhaps to a covered compost bin.
Another option is to spray plants with BT, or Bacillus thuringiensis, a naturally occurring bacteria found in soil. After mixing up powdered BT into a solution you spray the plants; caterpillars that ingest the bacteria ultimately perish. The good news is that BT won’t impact non-target species and, being a naturally occurring bacteria, it is totally safe and organic. That said, it can affect other butterflies and moths, so spray it carefully, making sure to spray on a still day and to cover only your brassicas. Spray uncovered plants regularly, according to the instructions, to keep them protected.
Step 3: Erect Barriers
All the measures above can be highly excellent, especially if used in combination. But the most secure step of all is simply to keep plants covered, so none of these pests can ever get anywhere near your plants! Let’s talk through the different covers you can use.
First off is butterfly netting. The holes are less than a quarter of an inch which is small enough to stop even the most determined butterflies from gaining access. To stop butterflies laying their eggs through the holes you’ll need to suspend the netting, so it’s held off your plants. A simple frame made of bamboo canes and upturned bottles such as this works well but be sure to secure it at the edges to stop them getting in at ground level. Or, staple netting onto a wooden frame to make a very simple but effective protective box for vulnerable seedlings.
Another option that we favor is tightly woven nylon insect mesh. It’s really durable, so should last for quite a few seasons, no problem. Despite it’s very closed look, it will let plenty of light and rain through, so you can just leave it over your plants. It will keep just about every pest out: butterflies of course, and cabbage aphids and cabbage maggots or cabbage root flies. (See video on how to set up and secure.)
Alternatively, you could make a temporary miniature hoop house then secure the mesh over that. These stand up to the wind really well, so are a great choice for more exposed gardens. (See video demo.) Plastic piping cut to size onto uprights of bamboo cane or rebar. If necessary, secure multiple hoops to a bamboo cane ridge, tied to the apex of the hoops with string (bamboo cane hanging down so it doesn’t slip to one side). Scrunch ends of the mesh cover together and weigh down with a brick then the secure edges with wooden planks. Because there’s significantly less chance of female butterflies or moths managing to lay their eggs through this mesh you can just let it float directly on top of the crops themselves once they’re a bit bigger and can support the weight of the cover.
Other covers to keep insects off include scaffold or debris netting.
And, as an alternative to insect mesh, you could even use dressmaker’s tulle or netting. It often works out a lot cheaper than the insect mesh, and you can even bung it in the washing machine at the end of the season, to freshen it up!
Then, for the winter months, you could swap to a wider mesh bird netting to keep those pesky birds off. It’s less likely to catch the wind and get blown away or have the snow weigh it down.
It’s important to have all covers in place in advance of any attack, so always err on the side of caution. And take precautions when removing covers to tend your crop or to harvest. Check around plants meticulously to avoid accidentally trapping a pest beneath the cover so it can’t escape – the worst possible outcome!
Check your covers regularly and make any repairs as necessary. A few small holes may go unnoticed but over time they will get larger, offering an open invitation to passing pests!