Black Spots on Kale | Causes, Prevention and Concerns

Kale Plant

Kale has become quite a popular vegetable to grow in the garden and for good reason. It has plenty of health benefits and can be prepared in a wide variety of ways. But what happens when black spots begin to appear on your kale?

So what are those black spots on kale? Black spots on kale are just decomposing or dead kale cells caused by a bacterial or fungal infection of the kale plant. When these infections start attacking the plant, they create toxins and proteins that destroy the plant’s immune system. This in turn, causes the plant cells to die off.

Nobody wants their kale littered with black dots of death. But, with the proper treatment and care, you can prevent these bacterial and fungal infections from attacking your kale in the first place.

Is it Safe to Eat?

But first, let’s address the elephant in the room. Is it safe to eat Kale with black spots on it? Yes. It is safe to eat kale that has black spots on it. It may not taste very good as you are consuming dead kale cells, but it is still safe to eat nonetheless as long as it is properly sanitized prior to eating.

You may think that consuming such kale wouldn’t be safe, but the bacteria and fungi infecting the produce have evolved to infect a plant’s immune system, not a human’s. Just be sure to give all your kale a good wash before consuming.

For good measure use some organic vegetable sanitizer to clean your produce. This will clean the kale more thoroughly than a simple water rinse and in turn, diminish the risk of food poisoning.

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What Causes Black Spots on Kale?

Black Spots on Kale

The most common cause of black spots on Kale is the leaf spot. There are two primary types of leaf spots. They include bacterial leaf spot and fungal leaf spot. The appearance, as well as the effect in both cases, are relatively the same.

Once a plant is infected with leaf spot, it develops black or brown spots on the leaves. Sometimes, the black spots have a yellow halo on them. Besides, the spots are usually the same size. In wet conditions, the spots become enlarged and run together.

In dry weather, the spots will have a speckled appearance. An increase in the number of black spots on the leaves causes the leaf to wither and drop. This is because the black dots are clumps of cells that are dying off.

The black spots on Kale also slow the growth of the plant. As a result, the plant becomes susceptible to other diseases or infections. Both bacteria and fungus leaf spots excel in warm and moist temperatures.

Hence, they are more likely to occur in summer. Watering your Kale through the use of overhead sprinklers in summer will also give your plants sufficient moisture that, in turn, will cause infection. Wind and rain also transmit the leaf spot bacteria to plants in your garden.

Moreover, once an infection occurs, the disease overwinters in the soil surrounding the infected plants. The disease remains in the garden debris, seeds, leaves, stems, and fruits from the infected plants and trees.

There are different forms of leaf spot. Nevertheless, the most common type of leaf spot that affects kale plants includes the Alternaria leaf spot and bacterial leaf spot.

Alternaria leaf Spot

Alternaria leaf spot

The black spots on Kale can be a result of the Alternaria fungal disease. The disease occurs once the fungal spores land on the plant and the conditions for growth are conducive. Alternaria alternata is the fungus species that causes leaf spots in Kale.

 The Alternaria creates asexual spores in the spots of the infected leaves. These spores are known as conidia. In case there is a sudden drop or rise in humidity, the conidia can fall. Air currents can then carry the fallen spores to surrounding plants.

When the conidia land on the kale leaves, they wait until nightfall when the dew point rises. The humidity present during this time allows the conidia to germinate. Within 12 hours, the fungus will penetrate the leaf, take hold, and start to spread.

The first sign of Alternaria species on your leaf will be the presence of yellow, dark, or brown spots. As it spreads, more spots begin to appear on the kale leaf. Severe cases can lead to damage and eventually wilting, withering, and dying of the leaf.

Further damage can spread to the stem, and if large areas are affected, the entire plant will fall. Alternaria can also affect the plant below the soil and into the roots.

Bacterial leaf Spot

Bacterial Leaf Spot

Bacteria leaf spot are the second cause for black spots on Kale. These are caused by the family of bacteria known as Xanthomonas. Unlike the Alternaria, these types of bacteria will overwinter in plant debris but will not survive long on soil or water alone.

The bacteria are weak pathogens. Hence, they require openings like lesions to infect the leaf. Insects are the primary source of the lesions that the bacteria use to affect a plant. Additionally, the bacteria are seed-borne making it easy to spread to nearby plants.

Splashing water or using overhead irrigation encourages the growth of the bacteria. If the moisture is prevalent, the disease can spread very fast since it thrives in wet, cool conditions. Therefore, one can deter the spread of the bacteria by exposing the plant to dry conditions.

The Xanthomonas bacteria produce small and angular spots that have a yellow tint. In the early stages, these spots appear water-soaked. When the lesions are older, the spots dry out. The lesions will quickly turn black once the infection occurs.

In extreme cases, the lesions will increase in number and combine, causing premature defoliation. The kale leaves will then become brown and wilt. Since the bacteria thrive in moist conditions, frequent rains can encourage the growth of bacterial leaf spot.

Using irrigation systems to water plants can also facilitate the spread of the bacterial leaf spot disease. However, without the plant, the bacteria cannot survive in soil and water. The moist conditions only make it easy for the bacteria to germinate.

Preventing Black spots on Kale

There are different methods that you can use to prevent the occurrence of black spots on Kale. One, you can try to buy a variety of plants that are resistant to leaf spots. Two, ensure that the soil under your plant is kept clean at all times.

Three, once you have raked and cleaned your soil, you can place a thick layer of mulch on it. The mulch cover will reduce the growth of weeds. This will prevent the disease pathogens from splashing back onto the leaves.

Four, ensure that your garden has good air circulation. You can do this by pruning or staking plants. Remember to disinfect your pruning equipment after you cut. Lastly, try and ensure that the seeds of transplants for your Kale are from stocks that experience no leaf spot.

This is because most cases of leaf spots are introduced by infected seeds or transplant.

Treating Black spots on Kale

Curing plants that are affected by leaf spot is impossible. However, it is possible to treat infected leaves and plants through several methods.

Neem Oil Method

Neem oil is an excellent preventative for many pest types. This is because it makes an environment that is inhospitable for the pests to thrive. Thus, it makes it less likely for the disease to spread.

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Baking Soda Method

You can spray a baking soda solution on your leaves to treat the black spots. To make the solution, add a tablespoon of baking soda to two and a half tablespoons of vegetable oil, a tablespoon of liquid soap, and a gallon of water.

Do not use detergent in the place of liquid soap. Spray the solution on a few leaves and see their reaction. If the baking soda burns the plants, do not continue with the treatment. If it works, you can then spray the solution on the remaining kale leaves.

Pruning Method

Pruning is another excellent method of treating the infected kale leaves. You can cut the infected leaves to stop the spread of the bacteria and fungus. When pruning the leaves, ensure that the cuts you make are sanitary.

Also, sterilize your pruning equipment by dipping the shears in a solution of one part bleach and ten parts water. You should clean the equipment between the cuts to prevent further spread of the disease. Also, wash your hands between pruning plants to reduce the spread of the fungus and bacteria.


The black spots on Kale appear because of bacteria known as Xanthomonas and fungi known as Alternaria alternate. Both the bacteria and the fungi are preventable, but it is still possible for your kale leaves to be infected. The good thing is that the black spots are treatable.

Also, it is still safe for you to eat your Kale without worrying about infection. Nevertheless, if you want to enjoy the full nutritious benefits of your Kale, ensure that your garden is not a welcoming environment for leaf spot.

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