Tony O’Neill, gardener and author of the popular “Composting Masterclass” and “Your First Vegetable Garden,” combines lifelong passion and expert knowledge to simplify the art of gardening. His mission? Helping you cultivate a thriving garden.
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You always strive for that perfect cabbage to take home to the kitchen, but keeping them healthy and free from pest damage is necessary. Cabbages can be affected by root-borne issues such as soil deficiencies, and pests include a wide range of insects, slugs, and birds.
Here we will look at some of the common cabbage issues and how you can identify them, rectify them, or also learn how to avoid them in the first place.
Cabbage Pest Damage
Cabbage Looper Damage
If you find small yellowy-green caterpillars on your cabbage leaves that arch their backs as they move, then you have found one of the most common pests, the larvae of the Cabbage Looper Moth, which are found throughout the US, Canada, and Mexico.
In the UK and Europe, the cabbage Looper is known as the Silver Y. They have no middle legs, so they ‘loop’ forward to propel themselves. The adult daytime-flying moth is about 1” long, is gray-brown, and can lay nearly 400 eggs, hatching and feeding on the cabbage plant.
If you use chemical control, you must re-apply regularly and use different treatments so that the pests do not build resistance. An organic but more time-consuming method is to check daily and remove any larvae or eggs you find.
A barrier method may also help, such as a fine mesh too small for the moth to get to the crops in the first place, but you will need to ensure there are no gaps or holes anywhere as they will be attracted to the plant and will find any way they can to get in.
Read our article on Companion Planting and the plants that help deter pests …
Imported Cabbageworm Damage
Often initially confused with the Cabbage Looper larvae, the Cabbageworm are velvety green larvae that you may see have faint yellow stripes.
The adult butterfly (Lepidoptera) is known in North America and the UK as the Cabbage White, in parts of Europe as the Small White, and in New Zealand as the White Butterfly.
You are more likely to see this distinctive butterfly in your garden as it is bright and visible, a sure sign of an impending infestation.
Treatment and Prevention are the same as for Cabbage Looper, the ideal solution being to stop the butterfly from getting to the cabbage in the first place using an insect-proof mesh or horticultural fleece.
When transplanting young plants to their final position, a brassica collar placed around the base of the stem can act as a physical barrier to the butterfly laying its eggs. These can be purchased or made from roofing felt, carpet, or similar material.
Using an absorbent material is a bonus, as it can be soaked in a strong-smelling liquid such as disinfectant or kerosene, which may help further deter the pest from landing in the first place. A 4” to 6” diameter is recommended as a minimum.
Cabbage Root Maggot Damage
Cabbage Root Maggots, also known as Cabbage Root Flies or Turnip Flies, will be visible as small white grubs that eventually turn into adult flies that look like house flies.
The larvae feed on the roots, severely weakening the plants and causing stunted growth, and if the infestation is severe, the plants will die as their roots are eaten. Young plants, seedlings, and transplants are especially vulnerable to this pest.
Aphid Damage
Aphids feed on the sap of a plant, and cabbage aphids are often found in groups under the leaves. You may notice yellow curled leaves on your cabbages, and it is worth investigating inside to see if these blue-gray waxy aphids are present.
Encouraging predatory insects such as ladybugs and lacewings into your garden may help control infestations of aphids.
Removing the aphids by hand can save your crop – use a paper towel or cloth to wipe the aphids away, and spraying the leaves with insecticidal or natural soap can prevent re-occurrence.
If you want to make your spray, why not dilute a few drops of essential oils in a cup of water? The strong-smelling herbs listed in our Companion Planting article, such as Mint, Rosemary, or Thyme, have been known to deter these pests.
Cutworm Damage
Another moth larvae, the cutworm, hide under fallen leaves or the soil and can attack the plant’s stem, often near the base, cutting it down from where it gets its name. These are technically caterpillars, but these larvae continually molt until they reach their full length.
Easily identified by how they curl into a ‘C’ shape when disturbed, they can come in various colors, mainly black or brown, but can be green, gray, or even pink!
Visible pests should be picked off and disposed of. A preventative measure for vulnerable seedlings is to use a tin can with both ends cut off and push this cylinder down over the seedling, half under the ground, to stop the cutworms from being able to grab onto the plant.
Cabbage Disease Symptoms
Black Rot
If you notice any yellowing or damaged leaves that are starting to rot, remove them immediately. Black rot is a bacterial infection that works through the plant’s veins to the stem and can spread quickly and easily, putting your entire crop at risk.
A preventative treatment containing antibacterial copper can help, and crop rotation (only one crop group per area every three or four years) should help ensure this bacteria does not stay in the soil.
Using good quality heat-treated seed is a must, and when watering, avoid splashing the leaves as residual water may harbor wind-borne spores.
Commercial cabbage seeds marketed as black-rot resistant are now available.
Clubroot
A soil-dwelling fungus-like infection of the Clubroot roots leads to swollen and distorted roots and stunts the plant’s growth. Plants are at higher risk of infection whenever the soil is warm and moist.
The spores of this disease can contaminate the soil for up to 20 years, so take care not to introduce them by ensuring any seedlings are brought in from a known problem area.
Any plant that displays signs of stunted growth should be removed to check the root system for evidence of pest damage or fungal infection. If you notice swollen and distorted roots, with loss of the finer roots you would normally expect, then Clubroot is likely the cause.
Limiting the soil can reduce Clubroot, and crop rotation is always advised. Clubroot-resistant varieties are available and should be purchased if you know that Clubroot is a problem in your area.
Fusarium Wilt
A fungus that can affect your cabbages, Fusarium Wilt, is most noticeable by a distinct yellow-green coloration of the cabbage leaves, often noticeable at the bottom of the plant more than the top (it works its way up), and also you may see that it affects one side of the plant more than the other.
If left on the plant, these leaves would turn brown and become brittle, and the plants will wilt, rot and die. As the fungus can survive, crop rotation and general soil management are necessary.
Downy Mildew
Keep your crops free from weeds to reduce the risk of weeds hosting Downy Mildew spores. If you see yellow discoloration on the tops of the leaves, with white patches underneath, then this may be the cause.
This fungal disease can quickly affect young plants and, on larger, more mature plants, can affect the central leaves (the cabbage crop itself), turning them brown.
Alternaria Leaf Spot
Another fungal disease affecting the leaves and heads of cabbages, Alternaria Leaf Spot, is caused by the Alternaria Brassicicola and Alternaraia Brassicae pathogens.
Also known as Black Spots, spots on leaves (clearest on the undersides) have a bulls-eye pattern with a brown to black center, and the area between spots can turn yellow. You may notice a yellow ‘halo’ around spots.
If your crop is affected, remove diseased leaves immediately; these will likely start on older leaves anyway. If the disease spreads to the cabbage head, noticeable by brown spots, your crop will likely deteriorate quickly, so keep a close eye on your budding crops.
Warm summers, especially after rain, can provide the right conditions for this disease to form, so try to ensure air circulates your plants by removing weeds, dead and infected leaves, etc., and be careful when watering not to splash water onto the plants, carefully water the soil instead.
Commercially available sprays are available, although organic gardeners may be limited to copper-based sprays if required.
Nutrient Deficiencies and Toxicities
Soil nutrients, or the lack of them, when the soil has been depleted through intensive previous crop growth or rain leaching the goodness from the soil over time, can cause growth problems for hungry crops such as cabbages.
Remember that a nutrient deficiency is not always the cause of damage to plants from the soil – you may have an excess of nutrients, which can become toxic to the plants.
Therefore, maintaining the balance is the key, starting with soil preparation the previous year and in the spring before planting, as well as planned crop rotation, general pest management, and keeping a tidy plot.
Here we list the main elements and minerals a cabbage crop needs to access through its roots. With careful preparation the season before, such as introducing fertilizers and bulk (digging in manure and compost), you can help maintain a balance and provide a good start for the crops. However, weather and other factors can still deplete the goodness mid-season, so here’s what to look out for:
Nitrogen Deficiency
If your cabbage leaves are starting to turn yellow, even a tinge of yellow, a Nitrogen deficiency is the first thing to suspect. Nitrogen easily washes out of the soil and can be absorbed into woodchips or sawdust if you incorporate that into your soil, so quick action can save your crop as a severe Nitrogen deficiency can cause heads not to form.
A Nitrogen deficiency can cause stunted growth and poor cropping. If you notice this yellowing of your plants (compare them to other crops, other cabbages), then applying a feed will help, and you should see results in a week or so, sometimes a lot quicker!
Nitrogen is the ‘N’ in NPK, the three major nutrients that plants need to survive and flourish, so using a high nitrogen plant feed (be careful not to over-compensate) or a balanced NPK fertilizer will give a good boost to plants.
Phosphorus Deficiency
More noticeable sometimes (but not always) as a red to purple tint to leaves, a Phosphorus deficiency can lead to severely stunted growth.
As Phosphorus can combine with other elements to form insoluble phosphates, the plants cannot access it, as they can only absorb a soluble mix of phosphorus ions. Phosphorus is only accessible by plants when the pH level is near neutral.
Phosphorus is the ‘P’ in NPK, the three major nutrients that plants need to survive and flourish, so using a high Phosphorus plant feed or a balanced NPK fertilizer will give a good boost to plants.
Potassium Deficiency
Most easily identified by scorched or browning leaf edges, leaves rolling to the center, and yellowing veins on leaves, a poorly developed plant that is not producing or has weak stems may result from a Potassium deficiency.
Acidic, light, sandy soils, or those affected by drought or high rainfall causing Potassium to leach from the soil, or soil too rich in Magnesium can be causes of Potassium deficiency.
Potassium is the ‘K’ in NPK, the three major nutrients that plants need to survive and flourish, so using a high Potassium plant feed or a balanced NPK fertilizer will give a good boost to plants.
Wood ashes are another good source of Potassium, so they are a free nutrient source, but too much may raise the pH of your soil.
Calcium Deficiency
Often caused by too little or too much water in the soil or the presence of too high a quantity of other nutrients such as those listed above, a Calcium deficiency is most easily identifiable as ‘tip-burn,’ which will start on the younger leaves. If young plants are affected, stunted growth can lead to cabbage heads not forming.
Light or acidic soils are likely to be affected and can be made worse during drought conditions.
Magnesium Deficiency
Starting on older leaves, and from the outside in, a yellowing that can progress to orange-red, the veins on the leaves may show a noticeable ‘chlorosis’ where the smaller veins are more chlorotic, that is where they are producing insufficient chlorophyll than the bigger ones.
Epsom salts (Magnesium Sulfate), always a gardener’s friend for yellowing beans and stressed tomatoes, can be applied to the soil or as a foliar feed.
Manganese Deficiency
A Yellow-green mottling on younger leaves and leaves that do not fold in as expected can be a symptom of a Manganese deficiency. Cabbages can be susceptible to Manganese deficiency when you have loose, over-limed, or high pH soils following drought conditions or cold, wet periods.
Ensuring organic matter is dug into the plot the season before, rather than in-season, can help reduce the risk of Manganese Deficiency.
Boron Deficiency
Affecting other brassica crops such as cauliflower and broccoli, somewhat more than cabbages, white cabbages, and spring cabbages (and all those lighter than the deep green traditional cabbage) can be affected by a deficiency in Boron. This unstable element can be easily washed away from the soil, so if your soil is thin, light, or sandy, has been over-limed, or is too high in calcium, Boron may become deficient.
A Boron deficiency is difficult to identify as it doesn’t show in the leaves; the insides of the roots may rot, spreading to create hollow stems, which can severely weaken the plant. You would need to undertake a soil test to be sure of a Boron deficiency, but symptoms to look for include internal cracking or rotting of the roots.
Boron is available as a commercial crop additive but is most easily applied by incorporating organic matter and compost into the soil.
If you use your dishwater to irrigate your crops, be careful of the detergents you use, which may be very high in Boron and too high for the crops that can become toxic.
Environmental and Cultural Problems
Taking time to consider the local environment in which your cabbage crop sits, the potential effect of weather, the effect of other plants nearby on your crop, and how to avoid pests and diseases, as we have already discussed, are key to ensuring a clean, healthy and nutritious crop of cabbage.
As we have already covered pests and soil issues, we will now take a look at some of the wider cultural and environmental considerations:
Water Stress
Over-watering and under-watering may cause significant issues – and of course, sometimes, these are outside our control; we can’t control the weather!
However, when it is dry, we can add additional moisture to the soil by watering, but covering the crop through the worst of the rains isn’t always an option. The perfect storm for cabbage damage is when heavy rains follow a drought, so when it is dry, rinse if you can reduce the risk of a spoiled crop.
Where cabbages have suffered from over-watering, the cabbage head itself can split right down the middle.
You will most likely see this when the cabbage is fully formed, so towards the end of the season, it tends to occur just when you think you’ve managed to grow that perfect cabbage!
Where cabbages are suffering from under-watering, the lack of water causes the leaves to turn yellow, as the plant cannot access the nutrients it needs from the soil, as these are carried in the water to the plant.
Keep an eye out for really dry soil and carefully water if you can, but avoid splashing the plants, as this can lead to fungal diseases.
Sunscald and Sunburn
Cabbages like a good deal of sunshine, but not too much or too bright, as this can cause sunscald or scorching in the harshest conditions due to overexposure to sunlight.
In the same way, humans suffer from sunburn, intense sunlight, high temperatures, and insufficient water cause plant stress and can damage the crop.
If you live in an area where you know you have scorching sun conditions, consider tall companion plants such as peas or beans that reduce the impact of the sun (see our guide to companion planting).
Poor Pollination
Most home growers grow from commercial seed and use the whole plant in season, and do not grow to collect seed but cabbages, as biennials, will produce flower stalks, although they cannot do this in their first season.
By sowing in the Fall, replanting in the Spring, and allowing them to bolt, you can end up with a seed spike, but be aware that these plants will likely cross-pollinate with other Brassica family members, so it is unlikely you will get a direct replica of your original plant.
Like most leafy greens, cabbages rely not solely on pollinators to set seeds or fruit.
Temperature Stress
Where temperatures rise above 80F and stay there for a while, cabbage crops stop growing due to the stress of the heat and eventually will bolt.
Cabbages also don’t like the extreme cold, so when regularly below 45F, it also stops their growing cycle.
Cabbages need around 60 days between these temperatures to flourish. So, to help your cabbages get through the worst of the heat and cold, shade cloth or tall companion planting for the sun, and frost protection, such as fleece on the colder days, can help.
FAQs on Troubleshooting Cabbage Problems: A Visual Guide
Conclusion
As we have seen, several factors can affect your cabbage crops, from soil deficiencies and excesses, environmental issues such as rain and sunshine, and those pesky pests that damage the crops, so it is all about preparing for the crop, keeping an eye through the year, and adding carefully considered additional mid-year nutrients and fertilizers.
It is all about balance, ensuring the ground stays moist and doesn’t dry out, helping the soil hold enough moisture for the crop, and allowing it to hold those valuable and much-needed nutrients in the soil ready for the crop as it needs.
Cabbages are in the ground for a long time, so a regular check on them can identify issues before they cause significant damage, and make sure you can take home and into the kitchen those prized heads of cabbage.
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