Every year, pests and diseases are looking to make a meal out of your cabbage plants.
In fact, I always plant extra in case cabbage pests decide to come for dinner. I’ve even taken matters into my own hands and built a protective house just for cabbages, cauliflowers, lettuce, and kale.
Sometimes drastic actions must be taken to protect your crops from pests and diseases. Being knowledgeable about what to look for is the first step.
We’ve put together 12 of the most common cabbage pests and diseases to help you navigate the growing season.
6 Common Cabbage Pests
Cabbages are a member of the cruciferous vegetable family Brassicaceae, also called Cruciferae. They share pest and disease problems with many other species in this family.
If you need a refresher on how to care for cabbages, visit our guide. Then, come back here and we’ll talk pests.
Unfortunately, as much as we love cabbages, so do pests. They’re subject to infestations by numerous pests. Let’s start with one of the most common:
1. Cabbage Worm
Cabbage worms are the larvae of the infamous cabbage white butterfly (Pieris rapae, formerly Artogeia rapae). This pest is a regular visitor to gardens, fields, homesteads, and greenhouses.
You’ve probably seen the cheerful butterflies flitting around your garden. They start visiting gardens in the spring and stick around through summer, and while they’re a beautiful addition to the garden, the larvae that hatch from their eggs aren’t.
This pest is a particular nightmare because it’s common and targets everything from seedlings up to fully formed cabbages.
The adult butterflies lay eggs on the underside of leaves, and the young, florescent green caterpillars hatch and ferociously feed, chomping holes through the leaves and into the head.
The worms are just over an inch long and have five pairs of legs.
If you see the butterflies, assume the larvae are present. You can also examine your plants for green worms or signs of feeding. Be vigilant from mid-spring through early fall for clusters of tiny yellow eggs on the undersides of the leaves or the green worms.
This pest has a voracious appetite and can quickly devour your cabbage leaves. Not only that but if the cabbage heart has formed, large, irregular holes appear.
You can hand-pick any pests you see, and floating row covers are the absolute best way to protect the plants without using chemicals. Parasitic wasps and ladybeetles will feed on cabbage worms, but if you use pesticides, you’ll kill these beneficial insects.
Learn more about identifying and dealing with cabbage worms in our guide.
2. Cabbage Looper
Native to North America and a known adversary throughout the US, Canada and Mexico, cabbage loopers (Trichoplusia ni) can be found in pretty much any garden where brassicas grow.
The adult is a medium-sized night-flying moth commonly known as the owlet moth and is in the family of Noctuidae.
The young larvae are green caterpillars or worms that resemble the cabbageworm. The two are often confused, but you can tell the difference because loopers have three pairs of legs in front and three in back. They use these legs to move in an inch-worm fashion, humping their back and straightening out to inch along the plant.
They also have faint stripes on both sides of their bodies.
The adult lays the eggs on the uppersides of the leaves. Then, the larvae hatch and they chew through the foliage of the cabbage plant. They will munch on the edges of cabbage leaves and, if left unchecked, can decimate an entire plant in no time.
They’re partial to cauliflowers, broccoli, tomatoes, lettuce, and spinach, too. Avoid planting these near each other, or you’ll create a welcoming environment for cabbage loopers.
Again, handpicking and floating row covers can help tremendously. Learn more about treatment and identification in our comprehensive guide.
3. Cabbage Aphid
Cabbage aphids (Brevicoryne brassicae) are small dark gray to green bugs, also called plant lice. They tend to cluster and build up in significant numbers. It’s not unusual to find so many of them on a plant that you can’t see the stem underneath.
They tend to cluster on stems or the underside of leaves where they’re hidden.
They feed by sucking nutrients out of the leaves using their straw-like mouthparts, turning the foliage a distinctive off-yellow color. They can also cause the plant to wilt as its depleted.
As their food source starts to fail due to heavy feeding, the females develop wings in order to head off and populate other plants.
When cabbage aphids are present, there will be sticky honeydew and a black soot-like covering on the leaves. This is attracted to the honeydew and is known as sooty mold. This mold reduces plant photosynthesis.
Thankfully, they’re easy to treat. You can simply spray them off using a strong stream of water and then treat plants with neem oil or insecticidal soap. Learn more in our guide to aphids.
You can pick the worst-infested leaves off of the cabbage plant and feed them to your chickens, too.
4. Cabbage Root Maggot
The larvae of the cabbage root fly or cabbage fly (Delia radicum) can be a devastating pest of cabbages.
Eggs are generally one-eighth of an inch in size, while the maggots are about one-third of an inch. Both the eggs and maggots are white. The adults look like small houseflies.
The larvae emerge in spring for those in the cooler, northern regions, and in fall and spring in warmer regions.
Adult females lay eggs near the base of young cabbage plants. Once hatched, the cabbage root maggots feed on the roots, causing stunted growth and, eventually, complete plant collapse.
At first, the leaves will exhibit wilting and turn yellow. Underground, the root systems will be compromised, thinning and becoming discolored.
You can use yellow sticky cards to determine if they are in your area. Once you can see that they are present, use beneficial nematodes to treat the soil and kill the larvae.
Next year, use row covers when planting to prevent them in the first place.
5. Cutworms
Cutworms are larvae of several species of night-flying moths. In the garden, you’ll primarily find Agrotis and Peridroma species. In terms of biology, cutworms aren’t actually worms; they’re actually caterpillars.
Their bodies can be solid brown, green, yellow, or tan, and might have a pattern of brown, green, or yellow flecks or stripes. They are usually about an inch in length, though there is variation depending on the species.
They’re called cutworms because they chew through the base of plants, cutting them off. One day, you have a happily growing cabbage seedling, and the next, you wake up to find that it has collapsed and is in a sad heap on the ground.
Both the adult and larvae are nocturnal, emerging from plant debris or soil at night to feed.
Cutworms will also slice the plant at the stem and drag the plant underground into its burrow.
There are species that will eat most vegetables and flowers, so few herbaceous plants are safe.
First, use exclusion methods, as they won’t impact natural predators. Plant collars are extremely effective. You simply need to place an empty toilet paper roll or something around the base of the plant to exclude the worms.
Diatomaceous earth will also cut the worms with its jagged edges and kill them.
Learn more about identifying and controlling cutworms in our guide.
6. Slugs and Snails
Our old friends, slugs and snails, will eat entire seedlings and chew huge holes in cabbage leaves. Use your favorite control method or heat to our guide to learn some tips.
These cabbage pests are soft-bodied, which is helpful in that they are susceptible to both preventive and insecticidal treatments.
6 Common Cabbage Diseases
Pests can significantly weaken plants and might carry pathogens that can infect your cabbages. So, disease control starts with preventing pests. With many diseases, the climate and the plant’s environment all dictate the risk posed by disease.
Any diseases can deplete cabbage growth and productivity can significantly reduce yields.
You can reduce the chances of any of these infecting your plants by watering at the soil level, spacing plants appropriately, keeping weeds out of the garden, and rotating your crops regularly.
When one crop of cabbages has been harvested, don’t replant in the same spot for at least a year.
Always dispose of diseased plants carefully. You don’t want to put them in the compost. Place them in a sealed trash bag. Practice good sanitation of footwear, tools, and gardening equipment.
1. Clubroot
Clubroot is caused by the soil-borne fungus Plasmodiophora brassicae. This pathogen can remain in the ground for many years, reinfecting any cruciferous vegetables planted in the same area.
The pathogen thrives in cool, moist conditions, making it a particular problem in zones with heavy rainfall and temperate growing seasons.
It deforms cabbage roots to the point that the plant is unable to uptake sufficient nutrients to grow and develop to maturity. This leads to stunted growth and malformed roots. Then, the foliage wilts, turns yellow, and dries up.
If you dig down, the roots will be swollen and deformed, forming distinct club-like structures. Hence, its name.
This disease can decimate brassica crops, reducing the harvest or even killing the crops. If your plants are infected, you’ll need to pull them. Then, head to our guide to learn how to deal with it in the future.
2. Black Rot
Black rot is a common disease that infects cabbages. It’s caused by the bacteria Xanthomonas campestris pv. campestris.
The bacteria thrives in warm, wet conditions, and is a rapid spreader that attacks numerous species.
The first symptom appears as V-shaped yellow lesions on the edge of the cabbage leaves. It’s these v-shaped lesions that are a hallmark of the disease. Eventually, lesions turn black and extend across the entire leaf.
As black rot progresses, the plants are robbed of nutrients, leading to wilting and deformed head growth. Severe foliage damage can result in complete collapse and loss of the cabbage crop.
Even worse, there is no cure. This is a challenging disease to deal with, so the second you notice those V-shaped lesions, you need to start addressing it. Head to our guide on black rot to learn more, along with some preventative measures, so you never have to face it.
3. Powdery Mildew
Powdery mildew is a fungal disease caused by the oomycete Erysiphe cruciferarum. An oomycete is kind of like a fungus but it’s a water-borne pathogen and requires water to thrive and reproduce.
It primarily affects cabbage plants during periods of warm weather combined with high humidity, causing splotches of powdery white or gray spores to develop on the leaves and head.
Over time, this can cause wilting and stress, and reduces photosynthesis. Powdery mildew rarely kills the host plant unless it is stressed by other factors, but it can significantly reduce the size of the heads.
Luckily, it’s not that hard to treat. You can even use good old milk! Mix together one part milk with three parts water and saturate the plant once every five days or so until the symptoms are gone.
If the problem persists, visit our guide for more tips.
4. Downy Mildew
Downy mildew is a disease caused by the oomycete Hyaloperonospora parasitica (formerly Peronospora parasitica). Though it has a similar name to powdery mildew, they are unrelated and have different symptoms and treatment.
This disease thrives in conditions that are cool and moist, rather than warm and humid, like powdery mildew.
Gray fungal growth appears on the upper surfaces of cabbage leaves. This coating eventually covers the entire leaf surface. Severe cases can prevent the cabbage from photosynthesizing.
Leaves may also curl, become twisted and deformed, and eventually die back. Also watch for dark, necrotic spots. If you see symptoms, immediately start treating your plant with copper fungicide. This needs to be applied weekly until symptoms stop progressing.
Existing symptoms won’t go away, so you’ll need to prune them off or dispose of them on harvest.
Our guide to downy mildew has other tips.
5. Fusarium Wilt
Also known as fusarium yellows, a soil-borne fungus named Fusarium oxysporum f. sp. conglutinans. Fusarium infects hundreds of species, but this particular form is specific to cabbage and its close relatives.
It’s most problematic in warm, wet conditions, with temperatures between 80-90°F. You won’t often see it on winter-grown cabbage.
When the conditions are right, it attacks seedlings and maturing cabbages alike. Typically, it can take two to four weeks following the initial infection before symptoms become visible. So, by the time you see it, it has been developing for a while.
The pathogen can live in the soil, waiting for you to plant a host that it can reproduce on. It can also be transmitted in soil or infected plants.
The cabbages affected will become discolored and turn yellowish-green. Sometimes, this discoloration appears across the plant or it might just show up on half of it.
As the pathogen moves through the plant, the leaves start curling, and you’ll see brown develop on the stems. The lower leaves tend to be symptomatic first, followed by younger, newer leaves.
It can resemble black rot, but in black rot, the stems become black, and it has those distinct V-shaped yellow lesions on the leaf margins.
Plants will be stunted with poor head growth or they might die within a matter of weeks. If it gets cold after infection, the plant might recover.
Once it’s present, you can’t get rid of it. Remember, it’s in the soil now. Your best bet is to let the plants be an hope they still develop a head. Next year, plant resistant varieties and consider planting in raised beds or containers filled with fresh, new soil.
‘Bugner’, ‘Red Hollander’, ‘Resistant Flat Dutch’, ‘Wisconsin All Seasons’, and ‘Wisconsin Hollander’ are all resistant.
6. Alternaria Leaf Spot
Alternaria leaf spot is a fungal disease caused by the pathogen Alternaria brassicicola.
The fungus needs long periods of high humidity and warm temperatures between 68-86°F to spread.
Spores develop and move with the help of water and wind. They’ll attach themselves to new host plants, and the cycle repeats. The pathogen prefers 55-75 °F to start new infections.
It is characterized by dark brown to black spots on cabbage leaves. Lesions can appear on the thicker stems and the veins of the cabbage plant. As the lesions grow, the foliage becomes weak and wilts.
When spores are developing, purple, fuzzy growths will appear on the surface of the leaves. The pathogen can spread on wind, water, or be carried on tools or by flea beetles.
In severe cases the entire plant will be compromised and can’t be saved. But if you catch it early, spray your plants with a fungicide every other week or according to the manufacturer’s directions. Something like Bonide’s Fung-Onil is highly effective. Grab some at Amazon.
