Black Spots On Kale (Leaf Spot Causes, Prevention And Treatment)

If you’re noticing black spots on your kale, there can be a few different causes. And figuring out the right cause is essential for getting the treatment right. In this article, not only are you going to find out all of this, but you’ll also learn whether you’re still able to eat kale with black spots, and how to tell when kale has gone bad!

So keep reading to find out everything you want to know

So, What Causes Black Spots On Kale & How Do You Treat Them?

If you notice black spots on your kale then the chances are it’s suffering from leaf spot. Leaf spot is fairly common, and while it is possible to treat, it’s much better to try preventing it from occurring in the first place.

Here are the two main causes.

Fungal Leaf Spot

Leaf spot is one of the most common causes behind black spots on kale (although the spots can also be brown as well). It’s caused by a type of fungus called Alternaria Brassicae and if left untreated you’ll notice the spots becoming larger and larger.

As well as this, as it becomes more severe you may also notice that the dark spots begin to look more like a target with concentric rings appearing on them.

Awa: Fungal Leafspot -- leaf blight "Anthracnose" | Flickr

Alternaria Leaf spot is most likely to occur in conditions where the weather you’re growing your kale in is warm and moist, just as is the case with all fungus. As well as this, if you’re growing your kale in your garden, you should also make sure that you eradicate any weeds around your kale as they can harbor the fungus.

Bacterial Leaf Spot

As well as being caused by fungus, leaf spot can also be caused by bacteria.

Similar to fungal leaf spot, when your kale is suffering from bacterial leaf rot you’ll notice black spots as well as brown spots with yellow halos similar to the concentric rings previously mentioned.

The spots can range in size from 3/16 to 1/2 an inch, and they can appear absolutely anywhere on the leaf.

Bacterial leaf spot of pepper (Capsicum sp.) | Pathogen: Xan… | Flickr

Unlike fungal leaf spot, bacterial leaf spot prefer cool, wet conditions, and these are typically the conditions they thrive in. So you need to make sure that your kale aren’t staying wet for too long if you suspect it’s already present. This will increase the chance of it spreading from plant to plant. (Just another reason hydroponics are preferable. You can keep your kale indoors and the leaves dry.)

As well as this, just like fungal leaf spot, the bacteria can also be carried in the seed of the plant itself.

How Do You Treat Leaf Spot?

There are a couple of ways you can try to treat leaf spot, however, you should try to avoid it getting this point in the first place. While treatment is great, prevention is the real winner.

Fungicides (Fungal)

While there are a number of different ways you can treat leaf spot, in most cases, it’s going to require fungicides (which may not be for you, if you’re growing kale from home).

If you’re an organic farmer you can use captan or copper fungicides, however, if you don’t mind using something more powerful then you can use some of the more commercially available fungicides as well!

Neem Oil

If you’re deadset against using any sort of fungicide, then neem oil can be a great choice. It’s a natural insecticide and people report having great success with it.

And the best part is you can still eat plants that have been sprayed with neem oil. Just make sure that you leave one day between spraying your kale with neem oil and eating it. Just to be extra safe, you should also wash the kale thoroughly as well.

Remove Infected Leaves

When you notice that leaves are infected you should remove them and ideally burn them immediately. And if most of the kale is infected, then oftentimes the best thing you can do is to remove the kale completely so it doesn’t spread the bacteria to other plants in the vicinity.

Spray Them With Baking Soda

Another natural method that people have had success with is spraying their kale with a baking soda mix. To prepare this mix just add a tablespoon of baking soda to two and a half tablespoons of vegetable oil, a gallon of water and a tablespoon of washing up liquid.

With this method you need to make sure that your kale can handle it. So only spray it on a couple of leaves and leave them for 24 hours. If you notice that they’ve been damaged then this method isn’t right for your plant.

How Do You Prevent Leaf Spot

As previously mentioned, when it comes to leaf spot, it’s much much better to prevent it from happening in the first place. Fortunately, there are plenty of things you can do to reduce the chance of leaf spot occurring!

Buy Disease Free Seeds

The first option is to buy seeds that are disease free. Obviously, they’re going to cost a little bit more, but it’s still going to be much cheaper than if you buy seeds that are already plagued with leaf spot.

Disease free seeds work because they’ve been heated to 122°F for 15 minutes which kills any harmful fungus on them.

Add Mulch

Mulch is great because it helps to reduce the spread of Alternaria Brassicae spores. Of course, it’s only going to be effective if you’re growing your kale in soil and not hydroponically.

And not only does mulch reduce the spread of spores, but when you keep it moist it helps healthy microorganisms thrive as well. On top of this, it’s also going to keep your soil moist for longer!

Keep Good Airflow

This ones pretty straightforward. By making sure there’s good airflow between your plants you’re going to be able to ruin the conditions fungal spores thrive in, as well as making it harder for them to spread from plant to plant.

This is one of the reasons it’s a good idea to give space hydroponic kale about a foot and a half away from each other.

Remove Cruciferous Weeds

Once again, if you’re growing kale outdoors, you need to make sure you’re keeping on top of cruciferous weeds. In the winter months, Alternaria Brassicae can winter on weeds, and once you start planting again, they’ll be ready to spread to your crop.

Crop Rotation

If you’re growing your kale over long periods of time, make sure you’re rotating the soil they’ve been growing in. You may not know this, but the spores and fungus actually become specialised to specific plants.

So by rotating the soil, the plants are being grown in, the spores are never going to have enough time to become specialized and this will reduce the chance of your kale suffering from leaf spot.

When you’re rotating your plants around you should rotate them every 4 years. If you’re growing anything cruciferous, however, 2 years is the much more appropriate.

Keep The Soil Clean

And lastly, make sure you’re keeping the soil clean of any leaf litter or natural debris that may fall into it. Spores will thrive in conditions where leaf litter etc is left to rot.

So by keeping the soil clear of these you’ll drastically reduce the chance of your kale becoming infected.

Avoid Cross Contamination

You also want to make sure that you’re avoiding cross-contamination as well. For example, if you’re pruning or doing anything with diseased kale, make sure you’re washing all the utensils thoroughly or even better, using tools that haven’t been in contact at all.

Remember both forms of leaf spot are extremely easy to spread, so this is a must when prevent it from occurring.

Is It Safe To Eat?

If you’re worrying about whether you should eat kale with black spots then the chances are you’re going to be completely fine. However, it’s still not recommended as it probably won’t taste good at all.

And most importantly, remember if you’re never sure about whether you should eat your kale or not, it’s always best to just throw the bad bits away and only eat the good bits.

To be sure that there’s nothing wrong with your kale, you can also use a vegetable sanitizer to remove any potential nasties that could still be on the kale.


Now you know that if your kale is suffering from black spots, then it’s suffering from leaf spot. While treating leaf spot is hard, preventing it is a lot easier.

So remember, if you notice that your kale is suffering from leaf spots, you can try neem oil, baking soda, fungicides, or for best results, removing the leaves altogether.

And to massively reduce the chances of your kale suffering from leaf spot make sure you’re buying disease free seeds, adding mulch (if planting in soil), keeping the airflow good, removing weeds, rotating your crop, keeping the soil clean and avoiding cross-contamination.

If you do all of this you’re going to grow some great kale!

And lastly, if you liked this article make sure you check out the rest of the website! Otherwise, have a great day!

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