Black Spots on Cactus

Black Spots on Cactus (Identify and Prevent)

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They are compact, easy to plant, easy to maintain, can easily fit even in a small cup, yes, we are talking about cactus. We know there is even gigantic size of these. But you won’t have them as your desk decor or home, right?

Cactus are both very hardy and relatively trouble-free species. However, some minor errors may lead to diseases and pests. 

The place in black looks like the word. The plant surface produces black patches on the epidermis. These spots can be damp or dry and spread under the dermal surface, depending on the rot type.

This happens to most cacti hobbyists. But the solution to this problem is relatively straightforward. This article will get you through some specific steps to help you eliminate these black spots from your cactus. 

Types of  Black Spots on Cactus (Identification)

Before you get started with the black spots, you have to determine which kind of place it is. There are two types of them. 

  • Soft Rot

Soft rot is a bacterial infection. The damaged cactus tissues join these bacteria, and they cause agaves root and crown red, along with bacterial necrosis in the saguaros. 

Soft, wet, decaying, tan and creamy tissue signs include soft rot. The rotting starts on the top of the tuber and advances inward. A healthy tissue sharply characterises tissues tainted by dark brown or black edges. 

Plant tissue becomes soft and watery. Soft rots commonly occur on fleshy vegetables such as potato, carrot, eggplant, squash, and cactus.

  • Dry Rot

Several fungi, especially Phyllosticta concave and Mycosphaerella species, are responsible for the dry rot. On the cactus, tiny circular black spots form slowly up to 2 inches. 

The dry red is due to the digestion of certain fungi that offer strength and steepness to wood sections. Dry red is popular on sticky pear pads, with brown rims like wide dark eyes. 

In places concealed outside, such as under floorboards and behind a wall, dry red is also found. It will inflict significant timber damage and spread through the house if it is not detected early on. A surveyor should always determine the full extent of the injury.

There are many more reasons behind black spot occurring on cactus. Let’s know them first. It’s important because according to the problem, you have to take steps to solve them. 

  • Bacteria

Because of fungal diseases, cacti can have a black spot, such as body necrosis, coronary red, and pad spot. Erwinia carotovora bacteria will invade your cactus in the event it is damaged or cut off. It multiplies the entire plant and infects it. 

Identification: Appearance of watery dark, soft tissue. 

Erwinia cacticida is another bacterium which spreads through roaming insects and polluted soil use. This infection can destroy the whole plant. 

Identification: Contaminated spot gets brown or grey.

  • Frost Attack

Most cactus species’ freezing temperatures are an enemy, especially if exposed for a long time. The exposed parts turn black that dries out and gets narrow. Cacti plants are generally beginning to rot exposed to freezing temperatures. Frost damage, however, will damage plant cells that have been exposed to cold temperatures. 

Coastal areas, deep deserts, high deserts, mountains and the other regions are the source of cactuses. Many cactus species may tolerate cold temperatures, though some cannot accept winter humidity. Depending on the species, the lowest temperature a cactus can survive.

  • Overwatering

Too much water overfills and causes the plant to blow and explode in storage tissues of water. The black spots are fungi which have developed in the damaged tissue of the plant. 

They can survive their native desert’s harsh conditions. Because of damaged root conditions, the plant suffers from insufficient nutrients and water. The slow death of cactus that are severely damaged and those black spots are signs of decay.

  • Extreme Sunlight

The leaves may be sunburned if the spots on the plates are bare. Yeah, too much sun will burn your sun-loving cactus. This occurs when it gets bright light from the plant before it has time to acclimatise. 

You can end up in a burned blade if you are buying a plant in the shade of a kindergarten, put it on your sunny deck, or move a succulent indoor-outdoor room.

  • Underwatering

Similar to overwatering, underwatering is also a reason behind your cactus is having black spots on them. The misconception is that cactus require no water, but that’s not true. It will fade and sleep to survive if you don’t water your cactus, especially during development. Do not foresee growth or blooming in this case.

  • Wrong/over Fertilization

It would be best to abstain if your cactus suffered from incorrect fertilisation. The apparent sign of an issue is when the black spots appear in your cactus. 

You must exceptionally be careful with the application of fertilizers in cactus because this does not take long. An excess of fertilizer in the soil can lead to salt growth.

Black Spots on Cactus ( Prevention)

  • Prevention for Bacteria

Remove the damaged areas immediately. This will help to prevent the disease from spreading. 

The best way is to get rid of the plant if the infestation continues and irreparable damage. When you do, make sure you don’t leave any trace. 

You can decrease the amount of moisture around them by exposing the infected cacti under the sun. This inactivates the bacteria.

  • Prevention for Frost Attack

First of all, know your cactus if it is immune to cold or not. Secondly, place it near a fireplace when it’s winter. It will need extra heat for warmth. You can also use artificial lights. It will provide additional warmth that would help dissipate the coolness.

  • Prevention for Frost Attack

Perhaps you can’t save your delicious one. Deposit the plant and check its roots for protection. If so, cut off the leaves and stalks that were damaged and repot them in dry soil. Overwatering cactus should be avoided from the same issue. 

You will allow it to sit without water for a longer time before it comes in shape again.

  • Prevention from getting sunburned

The sunlight must be optimised for the cactus. Place it on the first day in the sun for three or four hours. Sunlight rise by an hour or two a day. At night, put it in full shadow. The plant will be accustomed to sunshine by the fourth or fifth day.

  • Solution for Underwatering 

Make sure your cacti are watered all year round. Many underwater cactus lose their roots, so you have to water them with little water and gradually raise quantities. Make sure your cactus dries through the waterings.

  • Solution for Wrong/over Fertilization

If you are sure you have over fertilised your plants, Skip The Next Fertilizer Application Schedule. Your plant surely needs time to recover from the damage. Aside from that, the soil will also have a rest period.  

Diluting can also be a great way to handle the situation. It reduces the original strength of the fertilizer.

Treating A Cactus With Black Spots

Whenever you see big black spots covering whole regions of your plant, the infection is very advanced. Although it may be time and challenging to save your household, you can still do whatever you can to keep your Cactus alive.

Follow these steps to treat an infected cactus. 

  • Remove infected  Arms

As all cactus disease persists and goes without interruption, you must avoid it. The tainted pieces of cactus must be eliminated here. 

Start to cut where the cactus is black with slicing shears or even a gardening knife. You want to do three checks: before and after missing you sterilise the cutting instrument. 

Unsanitary tools can quickly disperse and destroy bacteria or fungi to other plants.

  • Change the Soil 

When you remember diseases such as crown rot in this article above, they tend to linger in the soil. A case of crown rot may be handled by chopping into the cactus, but if the ground is left untreated, the plant will probably be red again. 

And if the cactus doesn’t appear to suffer from a coronary rot situation, removing the soil is not a bad option.

  • Isolate 

Your cactus should be relocated. Either two or three more plants or dozens of another indoor greenhouse, fungal and bacterial diseases can spread quickly to susceptible plants.

Some Important FAQs

These are some questions and answers commonly asked by the cactus owner suffering from black spots on their plant. Check them out, and they may be of great help.

  • Why is my cactus turning black at the top?

It could turn black because the cactus is tainted with a disease of bacteria or fungus. This can also arise if you overwater or submerge the vine. A temperature variation may also be a cause for black spots.

  • Do cactus get white spots?

The sticky white hills are the houses for mealybugs. If the white, adhesive spots tend to emerge, it is safest to scrape them off the cactus pads with power dust applied to the tube at the top.

  • How do I know if my cactus is healthy?

Take your plant out of the soil gently if you want to check your root’s wellbeing. White should be stable roots, whilst purple, black or mushy roots should be decaying. If the rot spreads unchecked to other areas of your plant, your plant will be destroyed.

  • How often should Cactus be watered?

In summer and spring, the plants should be irrigated at least once a week in the growing season. The soil should be adequately watered so that that excess water will flow out. Let the compost dry between waterings somewhat.

  • How long can you leave a cactus without water?

Typical cactus can live without water for up to two years. It has dense stems containing a lot of water and a waterproof coating that prevents water loss.


As a cactus owner, finding black spots on your plant is pretty much frightening event. You will be concerned about the health of your plant.

The best way to save your plant is to identify it at the beginning and prevent it immediately. There are many more ways to do it. 

In this article, we have tried to bring upon the most straightforward steps that can be done by yourself. So go through it thoroughly, we hope you will be able to identify and prevent the problem. Good Luck.

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