Why Does My Cactus Have Black Spots

Cacti and succulents commonly experience cactus black spot. If not addressed in a timely manner, it may have an impact on the plant’s health, appearance, and even survival.

Typically, fungus or bacteria that invade through wounds in the plant’s skin generate the black patches on cactus plants.

However, chemical damage from fertilizers or soil additives can also result in black blotches.

You may find out how to notice black spots on cactus plants and the best way to handle this issue by reading the information below.

Fungal Diseases

When a plant is handled with unwashed hands or carelessly pruned with shears that haven’t been sanitized after use, the fungus can enter via any wounds in the plant’s skin.

There are several different fungi that can cause black spots on cactus plants; there isn’t just one kind that does it.

The most prevalent fungi on cactus plants include Cladosporium, Ramularia, Diplodia, and Botryosphaeria species.

How to Treat Fungal Diseases on Cactus Plants

Trimming away the diseased cactus plant sections with clean scissors or a sterilized blade and discarding them in a sealed bag to prevent the spread of the infection to other plants may be adequate for lesser infestations.

For larger infestations, it is preferable to apply a fast-acting fungicide, which you may get from your neighborhood garden center.

The type of fungus generating the black spots may require a different treatment, however mixing equal parts hydrogen peroxide and water is a solid overall strategy.

Use a cotton swab or brush to apply this solution to the affected plant sections and allow it dry completely before continuing.

In order to lessen the possibility of skin damage to the plant, you can also mix one part white vinegar with two parts hydrogen peroxide.

Bacterial Diseases

Xanthomonas or Pseudomonas bacteria, depending on whether they were introduced through wounds in the plant’s epidermis or through contaminated water and soil additives, may also be the source of black spots on cactus plants.

Despite being less frequent than fungi, these bacteria are even harder to treat.

How to Treat Bacterial Diseases on Cactus Plants

The vascular system of a plant is often infected by bacteria, necessitating considerably harsher curative measures.

Using the antibiotics oxytetracycline and streptomycin in combination is the most efficient way to treat bacterial black spots on cactus plants.

You must combine one part of each antibiotic powder with five parts water, then use a spray bottle to administer this mixture to all diseased areas until they are well saturated.

Cover the entire plant, making sure to include any healthy spots where the solution might drop.

Leaf Spot Damage

Leaf spot disease, which affects the plant’s leaves, can also result in black spots on cactus plants.

These lesions are frequently brown, round, and have a black border, which makes it simple to recognize this widespread issue.

Leaf spot lesions can form anywhere on the plant, but they frequently group together and enlarge with time.

If the leaf spot disease is not treated, it gradually spreads to the cactus leaves’ veins, making them brittle and prone to falling off.

How to Treat Black Spots Caused by Leaf Spot Damage on Cactus Plants

Pruning off the impacted plant leaves and relocating the plant to a more sunny location are the best ways to treat black spots brought on by leaf spot.

It will have more exposure to sunshine, which aids in promoting healthy growth, and this will help avoid new infections.

Chemical Damage

Most often, chemical damage from fertilizers or soil additives containing metals like manganese, zinc, and iron results in black blotches on cactus plants.

However, through water runoff, pollutants may also indirectly induce black patches on cactus plants.

The chemicals may be transferred by water droplets onto the plant’s surface if the soil has been regularly watered with polluted water, such as from a pool or hot tub.

How to Treat Black Spots Caused by Chemical Damage on Cactus Plants

One part milk and two parts water that have been boiled for at least five minutes must be sprayed on the plant.

Spray this solution on all afflicted areas until they are completely saturated.

In addition to supplying nutrients that could aid in promoting new development in the damaged areas, the milk aids in neutralizing the toxins that have burned through the skin tissue.

Sun Damage

Sun damage may be the cause of black patches on cactus plants that are not brought on by fungi, bacteria, or chemical agents.

Any black area on a cactus plant, in general, signifies that the skin tissue has been damaged and should be given extra protection from sunlight for at least a year while it heals.

How to Treat Black Spots Caused by Sun Damage on Cactus Plants

As the cactus heals, keeping it out of direct sunlight is the greatest remedy for solar damage.

If at all possible, plant the cactus in a spot with indirect light. Water it sparingly, and wait until the soil is totally dry before watering it again.

How to Treat Black Spots Caused by Pest Damage on Cactus Plants

If your cactus has been affected, it will need to be confined for a few weeks while the condition is treated because pests can quickly move from plant to plant.

Use insecticidal soap to kill the pests since it includes fatty acids that damage the pests’ cell membranes.

Although insecticidal soap is effective against a variety of insects, it should never be applied to plants that are exposed to direct sunlight since it could harm the plants.

For lesser infestations, you can simply mix one tablespoon liquid dish soap with two cups of water. Until the issue is fully resolved, you must repeat this procedure every five days.


If soft, mushy regions on the plant’s epidermis and black spots appear along with them, the plant may be showing signs of rot.

Rot is typically brought on by bacterial or fungal infections, though it can also happen when cactus plants are exposed to excessive moisture.

Any bacterial or fungal infection that enters the plant’s root system and hinders it from properly absorbing water might result in root rot.

Additionally, an infection that originates at the roots and moves up through the lower regions of the cactus plant is what causes crown rot.

Unless they have already sustained damage or are infested with pests like scale insects and mealybugs that weaken plant tissue and make them more susceptible to subsequent infections, cacti are normally not particularly prone to rot.

How to Treat Black Spots Caused by Rot on Cactus Plants

Making sure that your cactus plant is not damp for extended periods of time is the best technique to treat black patches brought on by rot.

It’s crucial to let the top layer of potting mix dry out before re-watering because rot typically occurs after the soil has been kept moist.

Repotting the cactus plant in fresh potting soil that includes some sand and perlite, which aids improve drainage, is required if you suspect crown rot or root rot.

If you decide to use cactus mix, be careful not to pack it too firmly around the roots because doing so could suffocate them and make it harder for water to get to the root system.

Assist the potting mix’s drainage by adding at least two inches of sand and perlite.

How are black spots on a cactus treated?

On saguaros or other dense cactus, remove any black areas that are under 2 inches in diameter using a sharp knife. All the way around the wound, cut away a layer of healthy tissue that is 1/4 to 1/2 inch broad and leave it to heal naturally. It is too late to cure a cut that is already oozing liquid or that is low on the plant. Maintain low humidity around plants and treat fresh wounds with a copper fungicide to avoid future issues. Agaves with the disease should be removed because there is no cure.

What do I do about the brown stains on my cactus?

Look to check if the brown spot and the vicinity are mushy and soft. If so, your cactus has probably started to rot from the inside out and is now displaying symptoms on the outside.

After noticing soft brown areas, the best technique to fix your cactus is to cut off healthy stems (without any signs of rot) and start a new plant.

Before cutting, disinfect a razor blade or a pair of extremely sharp sheers. Cut the cactus above the area of rot, allow it to dry, callus over, and then plant it again.

Use fresh soil, and thoroughly clean and dry the pot if you’re using the same one. Unfortunately, there isn’t much you can do to save your cactus as is once it has begun to decay.

In other words, the only method to revive a cactus that has developed rot is to cut off the healthy stems—those portions of the plant that are still green—and repot them in fresh soil.

What do the cactus spots on it mean?

What can we do to preserve the life of the cactus we adore? Some of the brown patches first appeared in December, and it is now expanding. It has always been wrapped in burlap and protected against frost with Styrofoam containers on the points. The same markings can be seen on other cacti (Mexican Fence Post) at Saddlebrooke. I would be very grateful for any assistance.

A number of factors, including excessive sun exposure on recently planted cacti, animal damage, frost, hail, some chemicals, and illnesses, can all result in brown blotches on cactus. Your cacti’s patches may be fungal lesions, which occasionally develop during periods of cool, rainy weather like this winter. The damage is typically only ornamental and won’t kill the plant, but it is also irreversible, leaving a scar. You should notice a decrease in the occurrence of this disease in your community now that summer-like weather has arrived.

How can black spots on succulents be removed?

Insects may be the cause if the spots are small and resemble a row of freckles. Mealybugs, spider mites, and aphids consume succulent leaves for their food, leaving behind tiny patches of dead tissue that later develop sooty black mold.

Remove and discard the damaged leaves as a solution. Use insecticidal soap or cotton balls dipped in rubbing alcohol to wipe the leaves to kill the pests. Continue the procedure every day until the nasties are gone.

What kind of plant are overwatered cactus?

The obvious indicators of an overwatered cactus caused by a fungus in the soil include black or brown blotches and mushy stems. It’s time to carefully chop them off with a knife if you experience any of these bodily symptoms. Use a sterilized knife while handling a rotting plant to prevent the spread of the infection.

You will have to exert more effort if the damage is severe. Essentially, what you’ll be doing is multiplying the portions of your plant that are still alive. Wear nitrile gloves to protect your hands from the cactus’ spines while you chop off the rotting sections, and exercise extreme caution when handling the plant. After cutting out the damaged areas, let your cuttings air dry for a few days, or around a week.

What symptoms do cactus sickness present?

Only the enormous variety of fungi can outcompete the great number of cacti species. Cactus pads frequently develop fungus spots, such as the Phyllosticta pad spot. Since treatments are typically the same, it is frequently irrelevant to identify the specific fungus that is causing the spots.

Once their visible harm is noticed, some fungal kinds attack the roots and finally the entire plant, therefore it is too late for the plant. Simple topical fungal spots are much easier to treat and, as long as the offending fungus is controlled, usually do not pose a threat to the cactus’ existence.

Cacti lesions can appear in a variety of ways. They could be square, oblong, angular, elevated, flat, or any other shape. Many are discolored, but once more, the hues might be anywhere from yellow to brown to completely black. Some are snarky, some are tearful. These may exude rust-colored, brown, or black fluid as a sign of a serious illness.

Opuntia and Agave cacti are the most frequently affected by fungal infections. Water spots or light discolorations on the plant’s epidermis are frequently the first signs of fungal diseases on cacti. As the fungus develop and spread over time, the symptoms may become more severe and may even eat into the cambium as a result of the surface skin breaches that allow the infection to enter.