How to Fix Black Spots on A Cactus

One of the most well-known house plants that is a popular choice for indoors are the Cactus. Apart from being distinctive in its appearance, this plant requires minimal care and can be adapted to extreme conditions like extreme heat and drought.

However, despite its apparent hardy nature, cacti can face serious issues, such as black spots.

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How to Get Rid of Black Spots on Cactus?

To eliminate black spots on cacti you must identify the root of the issue. Then, you’ll be able to identify solutions to avoid any further damage.

The quick solutions to this issue could include changing the light, controlling fertilizer and water, to reducing humidity, and protecting against frost, using mechanical, biological, and chemical controls to fight disease and pests.

It is essential to follow certain steps to get rid of those ugly black spots.

What Do Black Spots on a Cactus Mean?

If black spots begin to appear on your cactus, it’s the first sign of trouble. The plant is definitely stressed, possibly due to many causes, whether biotic or anabiotic.

The condition that is unfavourable affects the normal physiological cactus’s physiology and the resulting changes reflect on the outside of its appearance.

Causes of Black Spots on Cactus

Abiotic causes are the cause of black spot issues which are not living. For cacti, this could be excessive light or scorching, high humidity issues with watering fertilizer issues, and freezing damage.

On the other hand, biotic elements are those living organisms that cause issues within your Cactus plant. This includes insects, pests as well as fungi and bacteria.

We will go over each aspect further in the sections to follow.

Extra light/scorching

You’re probably wondering how the possibility for Cacti to get sunburn when it thrives in the deserts.

Although Cactus thrive in sunshine and bright environments, they also have some which were grown in greenhouses and nurseries in which light is blocked. This means they’ve adapted to this kind of environment as they grow.

If you attempt to abruptly move them in intense, bright sunlight, they’ll have difficulties adjusting to the light. In the end, your succulent will suffer from a sunburn and then turn to purple.

Cacti that are afflicted by burning heat turn yellow. In the latter stage, they begin decaying, and the black spots begin to appear.

How to Fix

Put Your Cactus Back to A Shaded Place

Cactus that are showing signs of sunburn must be returned to its original location to prevent further damage. It’s clear that it’s not prepared for sudden changes in response to exposure to light.

If you got it from nurseries, replicate the conditions there and recreate the same environment in your home as closely as you can. This will keep the cactus from being stunned by intense lighting.

Hairy Cactus in White Pot

Transition The Cactus To Brighter Light Little By Little

The cactus requires to adjust, and the adjustment process takes some time. This means you need to be patient during the period of transition.

Introduce your cactus to brighter light slowly small. This gives them the opportunity to slowly adapt to the new surroundings.

Watering Problems

Overwatering is the most common cause of death for Cactus. However knowledgeable people are about cacti not needing lots of water, they still are enticed by. Water can be both a friend and a foe to plants based on the amount you offer them.

When it comes to Cactus, excessive water can cause root rot, and we are aware of what will happen next. The plant is being deprived of nutrients and water because of damaged roots. Cacti that suffer severe damage by this condition will eventually end up dying and the black spots indicate decay.

How to Fix

Drain The Soil Immediately.

Examine the soil for signs of stagnant water , and then drain it quickly. Make holes in the container to clear the obstruction and allow air to circulate.

Take The Cactus From The Pot for Air Drying.

When the soil appears very damp and soggy it is possible to remove the cactus from the pot to make it easier to fix the problem. Place the cactus in a safe place and allow the roots to dry, as does the soil.

After drying after drying, you can place it back into the same container, but be sure to take out the roots that are damaged. Don’t water the pot following this time so that the roots can get some rest.

Skip Watering for Days Or Even Weeks.

Cacti that have suffered from excessive watering shouldn’t suffer the same problem. In this case you are able to leave it for a longer time without water until it is back to its normal shape.

High Humidity

Cacti thrive naturally in dry environments where they’re used to low humidity. They don’t require that much water because of their special stems that store plenty of water.

In addition, they possess an unique pathway to photosynthesis, known as Crassulacean acid Metabolism (CAM) which allows them to save water. (Source: Arizona State University)

Cacti are able to endure for longer even without giving them water. It’s reasonable to assume that they wouldn’t benefit from the extra humidity that’s in the atmosphere.

A humid and humid environment can pose a risk since it can trigger the development of pathogens that could possibly harm your Cacti.

In the presence of fungi and bacteria the disease will spread and affect cacti. This is the reason the plant has developed black spots.

How to Fix

Transfer Your Cactus to A New Location

The area should be cooler than the current climate. Avoid the kitchen or the shower area as they are extremely humid areas. If you put the cactus next to the window, be sure to move it at night to prevent cold drafts.

Run The Exhaust Fan.

If the humidity gets excessively high, you might require the assistance of an exhaust fan to draw the humidity out of your home. This is easier to accomplish when you have lots of succulents and cacti at home.

Beware of Humidifiers.

A few of your indoor plants might be a fan of the extra moisture , but your cactus will not. It is important to keep them separate.

Fertilizer Problems

A lot of fertilizer can cause serious harm to any plant, including Cactus. It is essential to be cautious when applying fertilizer to Cactus, especially since it doesn’t need as much.

Based on research by the University of Minnesota Extension, succulents and cactus require fertilizer just every once or twice. However, during these times, the fertilizer’s concentration is recommended to be cut down to half.

How to Fix

Leach Excess Fertilizer Using Water

A lot of fertilizer could cause salt accumulation on the soil. The salts are soluble, so you can leach them out using water. out the salts.

Continue to pour water in the ground until it drains out from the bottom. Repeat this process for 2 to 3 times. (Source: Penn State Extension)

Skip The Next Fertilizer Application Schedule

If your cactus is suffering due to over fertilization, it would be prudent to avoid adding fertilizers over the next days.

The plant will surely require time to heal from the damages. In addition the soil will be allowed to rest for a time.

Always Dilute The Fertilizer Before Use

The diluting of fertilizer aids in reducing the force of the concentration. Because potted plants are confined to soil, it is very simple to fill the pot with nutrients and water.

It is possible to reduce the fertilizer by the equivalent of half or even a quarter of its original strength. It’s enough to meet the requirements of your cactus as it’s not considered an extremely heavy feeder.

Freeze Damage

Certain cacti species can tolerate frost however some species aren’t. It is important to determine prior to purchasing if the species you have is hardy in winter. If not, it’s prone to damage from freezing.

Extremely cold temperatures are the adversary for a lot of cacti species particularly if exposed for a prolonged period of time. The exposed areas turn dark, which then dries and turns crisp.

How to Fix

Place Your Cactus in Areas Where Heat Is Radiated

It’s similar to putting yourself in front of an open fire when it’s cold. The cactus might not require a fireplace in the literal sense however, it will require additional warmth to keep warm.

Use Insulators such as Cotton Sheets

It can be used to cover your body when the temperatures are extremely low, particularly in the evening. Make sure you fully cover it to prevent any space that is open to cold air can pass.

Use Artificial Sources of Light to Add Extra Heat

The light of the sun can bring the cactus to life, particularly during winter. LED bulbs do not just help to make up for the lack of lighting during winter, but they also provide additional warmth to help disperse the chill.

Make sure you leave enough space (12 inches or less) between your light source and your cactus in order to prevent scorching.

Pest Infestation

The presence of insects could be the reason your cactus has developed black spots. The pests cause damage through their feeding on specific parts of the cactus and leaving lesions that change to either brown, yellow, or even black.

The most frequent pests found in cacti include the cactus longhorn beetle ( Moneilema gigas), cochineal scale ( Dactylopius coccus) Plant insects, the coccid scale, soft scale, and mites. (Source: University of Arizona College of Agriculture and Life Sciences)

How to Fix

Remove The Pests Manually Once Spotted

It is possible to control the majority of these bugs manually. All you have to do is be alert and patient in identifying any foreign species you spot in your Cactus.

Spray Water to Wash off The Insects

If you don’t wish to go through them individually, then using spraying with water is the best alternative. The force generated by spraying could be enough to remove the pests from the surface.

Make sure you dry the plant following this. We all know that excessive moisture is an enemy for cactus.

Apply Insecticidal Soap

If the pests become more persistent and continue to return then you can apply an insecticidal soap to eliminate them. It is simply necessary to dilute the soap in water before spraying directly at the pests.

It is possible to repeat this several times to eliminate these pests.

Leaf Spot Diseases

It’s also known as the Phyllosticta pad spot since it is caused by the fungus Phyllosticta. These appear as black spots in the pad of cacti like prickly pear.

When this fungus comes into contact with tissues, they release tiny white reproductive cells.

How to Fix

Isolate The Diseased Cactus

It is essential to distinguish plants that are healthy from those that require treatment. The reason for this is obvious. It is not our intention to allow any illness to be spread like wildfire.

Remove Infected Parts

If the damage is not too severe the removal is limited to the affected areas. Remove it from the plant in a proper manner. If the infection is serious it is necessary to dispose of the entire plant.

Exhibit Your Cactus in Bright, Direct Sun

The warmth will aid in keeping the pads to dry. This can help reduce the fungi’s effects by decreasing their activity. The aim is to make the pads dry so that the fungus will be inactive, even if it is not dead.

Fungal Diseases

Although we don’t see it as often, cactus also is a victim of fungal infections. Certain fungi kill a particular host, while others affect a variety of species.

Fungal diseases are triggered when the cactus is subjected to long periods of cold and wet conditions. Spores of fungi grow in this time of favorable conditions.

In the Texas Plant Disease Handbook There are five main fungi species that can cause cactus disease. They are:

  • Colletotrichum (Gloeosporium) spp.

The fungus is responsible for the anthracnose cactus disease, which manifests as wet, brown spots on the surface of your Cactus. The spots appear like rotten parts that appear initially small but grow with time.

In extreme instances, the brown spots may change from lighter to dark and black. The removal of the plant infected is essential to stop the spread of the disease.

  • Stevensea (Diplotheca) wrightii

The fungus is specifically targeted at Opuntia and is the cause for the occurrence of the disease known as charcoal spot. Spots can be as big as one quarter of an inch, and are enclosed by an elongated ring.

The size of the spots on charcoal tends to increase and also grow larger over time. If the cactus has become infected, it is imperative remove it completely.

  • Phyllosticta concava and Mycosphaerella Spp.

When these fungi infect plants, they trigger dry rot. The spots first appeared as tiny black circular dots, but then grew into quite large sizes up to 2 inches wide.

The tissues of callus also tend to grow on infected areas. There is no alternative but to eliminate the plant, too.

  • Hendersonia Opuntiae

The fungus is most commonly affecting Opuntia (again) as it can cause the sunscald or scorch. The affected areas show reddish-brown to black spots that get larger over time.

Cacti that are infected eventually die because the treatment for this disease is extremely difficult. It is necessary to eliminate the plant as well.

  • Phymatotrichum omnivorum

Another fungus causes a disease in Cacti. The most devastating aspect of it is that plants infected suffer immediate death, no matter how healthy they appear.

Bronzing and yellowing of leaves are common signs that are followed by the leaves wilting. Certain parts of the wilted leaves may display black spots.

  • Drechslera cactivorum

Stem rot is a simple way to kill your cactus , and is due to this fungal. The rotten parts can be seen in the apical or basal portions of your Cactus.

Dark brown to black spots can be seen in the swollen, soft stems. If you are infected, you may think that your cactus is dead in the sense that it is dead.

How to Fix

Discard Infected Cactus Plants

The majority of diseases caused by fungi are challenging to manage. To prevent spreading the illness, it is essential to eliminate the affected plant as quickly as you can.

The plant is protected by a seal and then dispose of them safely or burn the affected plants. Don’t leave it in your garden, as it could spread pathogens.

Apply Fungicides to The Remaining Cacti for Prevention

In the event that one of your succulents has been affected it is likely that your other cacti will contract the same disease. It is recommended to use fungicides as a method of preventing.

Move Your Cactus to Warmer Location

A humid environment can be an ideal fertile ground for fungi, therefore ensure that your cactus doesn’t get exposed to this kind of environment for long periods of period of time. Moving your plant to a warmer area will prevent fungal species from maturing.

Bacterial Diseases

Bacteria is another biotic cause that can lead to your cactus becoming ill and displaying black spots. As with fungi, bacteria are another type of pathogen that can kill any plant , including your favourite Cactus.

The most common bacteria responsible for ailments in cactus include the following:

  • Erwinia carotovora

A cactus that is injured or cut is the primary target for this bacteria. When it gets into the tissue through the wounds, it can grow and spread throughout the plant.

If the surrounding is humid the bacterium can multiply more quickly. The most obvious signs of infection are the appearance of soft, watery and black tissue.

  • Erwinia cacticida

Another bacterium can infect cacti, and specifically the saguaro saguaro bacterium that causes nec. The bacterium can be spread through wandering insects as well as the use of soils that are contaminated.

The area where insects feed is the primary place of infection, where the tissue beneath it turns dark brown to black. In severe cases, infection could cause the death of the entire Cactus plant.

How to Fix

Dry the Portions that have been swollen under The Sun

Wounds that are infected have become being inhabited by bacteria. They seek to remove the tissue and reproduce in the fastest way they can.

When you expose the cacti infected to the sun, you’re reducing the amount of water around it. The bacteria will become inactive.

Cut Back Infected Parts And Discard Properly

When you notice signs of the infection, you must immediately take out the affected areas. This will stop the spread of the disease.

If the problem persists and the damage is incalculable It is best to simply remove the plant. Be sure to leave no trace after you are done.

How to Prevent Black Spots on Cactus?

Black spots aren’t simply appearing at random. Based on what we’ve learned earlier, they are caused by numerous possible causes. The majority of them can be prevented If we only knew what to do.

Here are some suggestions to prevent the formation of black spots on your cacti plant.

1. Know Your Cactus First

When you purchase an unrelated plant, request for a brochure or a growing guide. It will be your guide to the most basic conditions that your plant requires.

The different species of cactus will require different treatment. To avoid the negative consequences of trial and error, you must know the cactus you have.

2. Purchase A Good Quality Cactus

Make sure to inspect the plant prior to purchasing. Examine the plant for signs of diseases and pests.

Does the plant appear vigorous and healthy? Don’t ever purchase plants that are diseased.

3. Mimic Its Natural Growing Conditions

If your cactus has to be moved indoors, you need to stay as close as you can to its natural conditions of growth. This means bright light and low humidity.

There are optimal conditions that allow certain cacti thrive. Make sure to keep these conditions as long as you can.

4. Watch Out for Drastic Changes in The Environment

Cold temperatures, high humidity and extremely bright light are all things to be aware of. Certain illnesses are more likely to manifest when conditions are favorable therefore you must be aware of that.

5. Use Sterilized Soil And Gardening Tools

The fungal and bacterial illnesses are often are spread through soils and equipment. It is a good idea to clean your pruning shears, shovels tools, and any other items that you employ in your garden.

This small act of protection can be a huge help to protect your cactus from disease. Always make sure to use clean, sterilized soil.

6. Check Repeatedly

Check the soil regularly to ensure it is not dry enough prior to you begin watering. Examine if there are any other organisms that are lurking in the soil. Make sure it is receiving sufficient sunlight.

Keep in mind that prevention can only be a reality if you’re attentive enough to spot the issue in the early stages. Therefore, make sure you check your Cacti.

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1. What is the cause of the black spots on Cactus?

There are many reasons that can cause dark spots to appear on your Cactus. As a general rule, you could classify them as abiotic or factors that are biotic. The abiotics are non-living organisms, while the biotic are the reverse.

It can be challenging to determine the cause initially, but it is helpful to know the symptoms and signs of every cause. This will assist you in deciding what solutions will be most effective.

2. What do the white spots on a cactus signify?

The white spots on cactus are likely caused by insects or pests who have found refuge in the plant. Particularly, the Cochineal scale ( Dactylopius coccus) is seen as white, cottony tufts that appear on the surfaces of the cactus pads.

Powdery mildew can be another cause to the white spots that you can notice on your Cactus. It’s a disease that is caused by an fungal fungus.

3. How can you eliminate white fungus that grows on Cactus?

To eliminate the white fungus that has accumulated on your cactus, you’ll have to apply fungicide to the affected areas to kill the fungus. It is also possible to make use of baking soda and soap water as alternatives to fungicides.

If the infection continues it is necessary to cut off the damaged areas. Create a more efficient air flow around your Cactus. To reduce the reproduction rate of spores, do not place your cacti in a moist environment.

Cacti plants might have earned the image of a tough plant, but that does not mean that it isn’t susceptible. Every plant has weaknesses and your cactus is certainly not without its own. However, that doesn’t mean that you won’t have a chance of keeping it in the house.

The black spots could appear normal at first. But, they can tell much about the overall condition of your Cactus. It is better to research and discover solutions before you be disappointed later on.



Went from a bad gardener to a half-decent one over 10+ years. Super happy to share my tips and tricks with you :)