Black spots on basil plants are worrying features that would get you thinking. Well, if you’re an experienced basil grower then you’d know that basil has its own set of enemies, and you should keep an eye out.

Black Spots on Basil Plants

So what exactly is making our green, fragrant shrubs go black? That’s what we’re here for, and to let you know that there’s a cure for every problem, so keep reading.

What Are the Reasons that Basil Has Spots of Black?

The reason that basil has spots of black on them are insects, bacteria, and fungi infestations, or due to temperature damage. In addition, they could also be because of poor nutrition in the plant, or the herb has been overwatered.

– Insects

Those pesky leaf miners may come in plenty of colors from white, to green and black. But you will always spot the leaf miners’ activity by black spots on leaves. And those black spots will be sooty mold that’s formed on top of the sap secretions made by these sap-sucking insects.

If you cannot identify the source of these black powdery smudges, you probably have issues with mealybugs, scale bugs, spider mites, or aphid insects. These insects are known to be ones that feed on the nectar of plants, and basil is one that has flowers.

To do this, they will attach themselves to the phloem of the plant, form some type of protective film and begin to feed. After doing so, they would start to grow in the plant and eat the rest of the nectar.

They will usually do this where the plant is weakest, which happens to be the foliage, as it is quite thin. They will eat the essential sugars and nutrients from the plant and then produce a compound placing it out to bring the sooty mold to finish the plant off. Note that if you’re growing your basil in the open, you likely won’t have any issues with insects though, because they would come from the environment as well.

– Bacteria and Fungi

And of course, this one concerns diseases caused by bacteria and fungi, as well. The most notorious of the basil-infecting bacteria are Pseudomonas Cichorii infection. These will create much larger and more profound black spots than insects will and if you find that your basil has been infected by this bacteria, you should throw away those black leaves.

Another damaging disease that could come from a fungus is Cercospora leaf spot. Being a fungal infection, this is also a bacterial leaf spot that will thrive where the environment is wet and warm.

Reasons that Basil Has Spots of Black

In addition, the number one cause for this one will be us, the humans watering our basil plants from top to bottom, instead of just soaking the soil, as they will develop in such a state. The black spots caused by this one are large and should be taken off the plant.

Moreover, you can also check this issue taking place due to a fungal disease, which is known as powdery mildew, and you can identify it by white and black powder-like patches on leaves that will leave a smudge if you run your fingers through them. All of the fungal infections will likely start at the top, so you will have the time to spot them and get rid of leaves before the entire plant is taken over.

– Temperature Damage

Black spot causes don’t always have to include external bodies, such as bacteria or insects. Frequent and sudden changes in temperatures can affect your basil leaves negatively.

Cold temperatures are the most usual of these, as basil loves mild and hotter climates. Exposing the plant to a prolonged period of cold will surely take some casualties in the form of black leaves. Hot isn’t such an issue, but sunburns are, which means that you must try not to splash those leaves in the high summer heat as the water and sunlight will burn them in a slow manner by first leaving little black dots.

– Poor Nutrition

Plants should always have proper nutrition available to them, as lacking nutrition can lead to black and burned leaves. And the riskiest element to play with is nitrogen, and the lack of it. It is essential for healthy plant growth, but can at the same time be deadly.

– Overwatering

Often, watering schedules will play a major part too; as a result, if we overwater the basil plant in the full sun, splashing basil leaves with water, we are inviting the sun to kill our plants. However, one more issue comes with overwatering, and that’s moist and soggy soil.

Overly wet soil can cause roots to die and plant to wilt, but you will see this sign of stress upon the leaves. In any case, nothing on your plant will remain green once the blackening effect of overwatering has set in!

How To Deal With Black Spots on Basil?

To deal with black spots on basil you should apply some neem oil, as you would do with your tomato plants, and get rid of the pests; make sure to disinfect your plant and the growing medium of the fungi and bacteria. Lastly, you should also try to provide the right requirements to see your plant thrive.

– Apply Some Neem Oil

Aphids and other pests causing black spots can be dealt with the use of pesticides. However, don’t reach straight for chemical ones. Those microscopic beings can be easily wiped out with much smoother homemade solutions, which would help you tackle away the insects.

Neem oil is ideal for this purpose and all you need to do is mix some with water and heavily spray your basil shrubs. Basil leaves aren’t all that pliable, so you shouldn’t rub the insects off of them.

Instead, you should also rely on cutting the leaves that are heavily infested, as your basil will spur new growth in no time, and even if these insects are upon the companion plants, they will repel from there too, and the new ones will grow in a healthy condition.

– Disinfect The Plant

Powdery mildew and other fungal and bacterial diseases won’t do much harm and kill your plant, this is such a rare occasion, but they sure look unsightly. If the disease has bitten too much into leaves, you can freely cut them away and expect your basil to grow new healthy leaves.

Deal With Black Spots on Basil

However, you should also try to protect your plant from developing further diseases, and for this, you want a disinfecting medium and a preventive medium. Disinfection is easily provided by rubbing alcohol and prevention by a fungicide, which general plant-based fungicides will do!

You can mix a small amount of rubbing alcohol with a gallon of water and add pre-bought natural-based fungicide to the mix. After this, you can freely spray over your plants, and disinfect them.

– Provide the Right Requirements

Those developing black spots aren’t only caused by bugs or diseases. How well and where you keep your basil plants will have a major impact too because the right requirements such as light, water, and nutrients are keen parts of its growth.

Sunlight is especially frightening here, and you should always provide a slight shade when the heat gets too strong in those summer afternoons. Moreover, note that as basil plants won’t be too fussy about their nutrition, you can always add some crushed eggshells into your potting mix or soil to ensure some nitrogen and calcium are released into the soil.

And last but not least, watering, which is why you should always try to be mindful of your watering regime. Look for a fine balance and never allow your soil to dry up, but don’t allow for it to be lovely and moist all the time.

In general, water your basil plants as soon as you see that the topsoil is somewhat dry and if you do skip a day, your plant will forgive you. Also, never water your plants’ foliage, because if you do so, the daily heat may cook the water droplets and leaves together with them.

Look to Keep Your Basil Plants


Those black spots on your basil plant are no joke and can be caused by more than one thing. While basil is a strong and resilient little plant, things can go sideways if you don’t pay attention to what we said:

  • Always take a step back and identify what’s wrong with the plant and make sure you recognize the culprit.
  • Although plants may benefit from the solution, you may not choose the right strategy, as insects and fungal diseases require different methods.
  • Look to keep your basil plants in a balanced environment. While that isn’t possible at all times, due to weather conditions, you can do your best to adjust fertilization and watering regimes.

That’s all there is to it, treat your basil plants with respect, and they’ll answer with abundant growth.

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