Caption
The cabbage worm, which is the caterpillar of the cabbage white butterfly, can be a dangerous pest in your garden.
Identification
How to Identify Cabbage Worms
Cabbage worms are velvety green larvae. They have a few faint yellow stripes. They are not to be confused with cabbage loopers, which are yellow-green caterpillars. Unlike cabbage worms, cabbage loopers raise and lower their bodies as they move (like an inchworm) because they have no middle legs.
Cabbage worms become cabbage white butterflies, which are primarily white with a few black markings. Cabbage white butterflies might seem like a pretty addition to the garden, but they are probably laying eggs on the undersides of leaves!
Where you find cabbage worms and cabbage loopers, you also might find the eggs and larvae of the diamondback moth and the zebra caterpillar. The camouflage of these creatures is excellent, so you will often see the frass, or fecal matter, that they leave behind before you see them.
Cabbage Worm Damage
After hatching in early to mid-spring, cabbage worms feed for two to three weeks before pupating. This is the time when monitoring is critical! Cabbage worms can happily eat away at young seedlings or the foliage of cabbage, cauliflower, broccoli, and other leafy crops. They feed on foliage, and eventually, they can leave plants with only stems and large veins. Cabbage worms can devour your crops entirely if left to their own devices. Their fecal matter can also stain and contaminate the produce.
Photo Credit: Purdue University.
Control and Prevention
How to Get Rid of Cabbage Worms
- Manually remove (handpick or squish) the eggs, if possible. Check the undersides of leaves and along stems.
- Yellow sticky traps will catch the adult butterflies, but may also catch beneficial insects. Use with caution.
- Spraying with Bt (Bacillus thuringiensis var. kurstaki) every 1 to 2 weeks will also help control cabbage family pests.
- Neem oil is effective against cabbage worms.
- Check with your local Cooperative Extension for your area’s regulations on chemical control.
- It’s said that if you dampen cabbage leaves and sprinkle them with cornmeal, the caterpillars will eat the meal, swell, and die.
- Old folk advice from The 1963 Old Farmer’s Almanac states: Years ago, people sprinkled rye flour over cabbage plants in the early morning. The flour dehydrated the cabbage worms. Give it a try!
Photo Credit: York College of Pennsylvania.
Prevent Cabbage Worms
- Cover your plants with row covers to deter the adult butterflies from laying eggs on the cabbages.
- Trichogramma wasps (very tiny; they do not sting humans) parasitize the eggs of the imported cabbage worm; these beneficial insects are available by mail order, although you’ll need to time their release appropriately—the mail order company would be able to help you. Paper wasps and ladybugs are also great predators of cabbage worms. Read more about beneficial insects.
- Companion planting is a useful deterrent for many pests. Cabbage worms are repelled by thyme, so it would be a good idea to plant thyme near your susceptible plants. Cabbage worms are attracted to mustard plants, so planting mustard near more valuable plants can be a good trap for cabbage worms. Once they take over the mustard, you can destroy the plant.
- Try planting red-leafed varieties of cabbage or lettuce. The cabbage worms won’t be able to camouflage as well, so they are less likely to choose these plants.
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It would seem a shame to discard a good harvest just because a relatively tiny pest left a few droppings on it. Cut out or cut off the parts that were pooped on. Wash the vegetable well, and cook as planned. Or, after cleaning them well, you could eat the vegetables raw in slaw or salad. But if you have any hesitation, cook it to eliminate your concerns.
About the purple cauliflower: There is a variety that is supposed to be purple. It grows that way. Are you sure that is not what you planted, or—who knows?—what you did not know you planted? Come to think of it, some white varieties may have a bit of purple on the stems of the curds (the clusters on the head). That is probably safe to eat but if you have any doubt, don't.
Don't let the insects bug you!
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