There are two sizes of cabbage white caterpillars gardeners should know. There is the small cabbage white caterpillar and the imaginatively named large cabbage white caterpillar. The smaller variety of this pestis an unassuming green worm, while the larger cabbage white caterpillar can be identified by its hairy black and yellow appearance.
Both the small and large cabbage white caterpillar are found across Europe, but only the small cabbage white caterpillar has made its way to North America, Australia, and New Zealand, where it is called an imported cabbageworm. Unfortunately, the different butterflies of these two worms lay their eggs at different times of the year, so brassica and nasturtiums can fall prey to these pests from early spring through autumn.
These bugs are commonly found on brassica plants, which include cabbage, cauliflower and broccoli. (You can find out more on these plants at in this Gardening Channel article: Brassica Vegetables: All Domesticated from This Plant.) Nasturtiums can also fall prey. So, if you find that the leaves of your brassica and nasturtiums are suddenly full of holes, the culprit is most likely one of the cabbage white caterpillars. The larger ones are more voracious eaters, but both types can do significant amounts of damage if left unchecked.
How to Identify a Cabbage White Caterpillar Infestation
The first sign of a potential cabbage white caterpillar infestation is the presence of the cabbage white butterfly. When the butterfly is present, then chances are they are laying their eggs on the brassica plants present in the area. These butterflies lay their eggs on the underside of the leaves. The small white lays single eggs, while the large white lays eggs in groups of 40 to 100. No matter the amount of caterpillars present, both kinds of caterpillar eat the leaves of the plant, leaving them full of holes. Despite being the smaller, and smaller-in-number, of the two, the small white caterpillar is more destructive. This tiny pest burrows into the hearts of cabbages and heads of broccoli, leading to discoloration and further damage to the plant.
How to Stop a Cabbage White Caterpillar Infestation
The key to stopping a white cabbage caterpillar infestation is to make sure that they are not given much opportunity to infest a garden in the first place. If cabbage white butterflies are spotted hanging around brassica plants, all types of plants that can fall prey to this pest should be covered in a butterfly netting. Just because the netting is there, however, doesn’t mean the plants are fully protected. The gardener should still do checks of the plants and remove any caterpillars they find.
Garlic has also been shown to ward off these pests. A garlic spray can be made at home and then sprayed on plants that are infected—or in danger of being infected. Cloves of garlic and water are the only two ingredients needed to make this all-natural remedy, and the amount of garlic added effects the potency. For a weak, purely preventive spray, you just need six cloves of garlic in a gallon of water. To fight a full-blown infestation, a more potent spray of two bulbs of garlic in half a cup of water will do the trick.
Making this spray is easy. Crush up your chosen quantity of garlic, and put it in a bowl. Add your chosen quantity of boiling water, cover it, and let it steep overnight. Make sure to strain the mixture before putting it into a spray bottle, and remove any large garlic pieces that could clog the nozzle. Spray this mixture, no matter the potency, every 10 days on any infested plants, or to try and avoid an infestation of white cabbage caterpillar. If spraying every 10 days does not seem to be doing anything, shorten the time between sprays, and be careful to respray after rainfall. Make sure to spray the underside of the leaves, where many pests like to lay their eggs.
If your garlic spray isn’t working, additional ingredients, most of which can be found in any kitchen, can add an extra kick. Hot red pepper, or hot pepper sauce, added to water while the garlic is steeping can help repel a larger variety of pests. Adding a thicker substance, such as dish soap or any type of oil, will help coat any larvae and smother them before they hatch. Make sure that if the plant you are treating is one you plan on eating, do not use dish soap. Oil is always the gardener’s best bet if the plant is going to be consumed.
There are natural predators for the cabbage white caterpillar. Most birds do not find them palatable, but house sparrows, goldfinches, and skylarks will eat them. If you live in an area where these birds are found, provide feeders and nest boxes to make your garden a more welcome place for these critters [https://www.gardeningchannel.com/landscaping-to-attract-birds-and-wildlife/] that will take care of a white cabbage caterpillar infestation for you.
Finally, just because the white cabbage caterpillar laying and hatching season is over doesn’t mean that a garden is safe. Once the caterpillars are fully grown, they will move away from the plants they eat to more sheltered areas. This can include fences, tree trunks, or the undersides of buildings. Here they will pupate for two weeks over the summer, or eight weeks over the winter. Checking these areas and removing any caterpillars you find is an important way to protect future plants.
Cabbage white caterpillars, whether large or small, can quickly destroy a crop of cabbage, broccoli, cauliflower, or rutabagas. If any of the cabbage white butterflies are seen in a garden containing these plants, then an infestation is probably already underway. Taking steps to avoid an infestation, by deploying any number of the strategies explained here, will go a long way in ensuring your brassica and nasturtiums continue to grow and flourish.
Abbie Carrier graduated from Texas Woman’s University with a Bachelor’s of Science in history and a minor in political science, and she is currently working on a Master’s of Arts in arts administration from the University of New Orleans. With this degree, she hopes to gain a position in museum curation, and she currently works as a grant writer for nonprofit organizations. She enjoys writing about the arts, history, politics, and topics related to science, health, lifestyle, and entertainment.
Want to learn more about how to fight cabbage white caterpillars?
Gardener’s World covers Cabbage White Caperpillars
Grow Veg covers Cabbage White Butterflies: How to Avoid A Brassica Massacre
SFGate Home Guides covers A Garlic Spray for Garden Pests
Oregon State covers the Cabbage White Butterfly
Somersetlive explains How to Get Rid of Cabbage White Butterfly