How To Treat Fungus on Cactus Plants (A Complete Guide)


Cactus plants are unique and interesting plants that are not only exotic but also easy to care for.

They are popular houseplants because they require little care, but the fungus can still grow on them if you don’t know how to treat fungus on cactus plants.

If fungus develops on your cactus plant, it may be challenging to get rid of the fungus. You will need patience and care to remove fungus from your cactus plants successfully.

If your cactus plant has fungus growing on it, this article will tell you all about the fungus that is causing the problem, as well as what you need to do to get rid of it for good!

What Does Cactus Fungus Look Like?

Cactus fungus is characterized by a soft, white mass that usually appears at the base of cacti plants.

It can also appear on stems and roots if it has spread to those areas.

Sometimes the fungus looks like cottony mold growing over dead plant matter. This type of fungal infection often starts in decaying plant material such as fallen leaves or flowers before spreading to live parts of a plant.

Other times, especially when there are no signs of other types of damage, it may be hard for an inexperienced person to tell whether they see what’s going on with their cacti or something else entirely.

What Causes Fungus on Cactus?

Several different things can cause fungus on cactus plants.

It could be as simple as too much humidity, or it could be something more complicated like root rot from overwatering.


One of the most common causes of fungus on cactus plants is overwatering.

This can happen when there are heavy rains, and it would be normal to water your plant, but you overdo it with too much water at once.

The same thing happens if you have a drainage problem or poor soil that doesn’t allow proper draining after watering.

If this happens, fungi will begin growing because the roots start rotting from being soaked continuously with water. Loose Soil Conditions

If your potting mix isn’t very good, fungus may grow even if you don’t overwater your plant since they aren’t getting adequate nutrients anymore either!

Make sure to get some quality potting soil (with lots of drainage), or do some research to see other options.


If your plant is in a small pot, humidity can become an issue.

This means that there isn’t much space for air to circulate around the roots and cause them to stay moist instead of drying out.

In this case, you might see fungus beginning to grow on top of soil or even near its base where it sits inside the pot.

If this happens, try repotting into a bigger container with better drainage, but also be sure not to take care of overwatering since cactus plants need less water when they are in larger containers!

Temperature Issues

Temperature issues could have something to do with why your cacti have developed fungus as well, though!

Cactus plants prefer warmer climates, so if you experience colder temperatures, fungus could become a problem.

If you see this happening, then it’s best to move the cactus plant into an area with more light and heat to grow nicely!

High Levels of Fertilizers

Another thing that can cause fungus on cactus plants is if you’ve been using high amounts of fertilizers.

The best type to use for these plants are those with low nitrogen and potassium levels, but make sure they aren’t too acidic (if it says anything about the pH level).

Otherwise, your plant will burn and end up dying or deforming itself from growing strange shapes/colors because it’s receiving too much fertilizer!

Plant Age/Conditioning

It’s possible that your cacti just isn’t as healthy anymore because of its age or condition.

When plants get older, sometimes their growth slows down, and leaves begin to fall off without any reason at all (this doesn’t mean anything – don’t worry).

It could be because the roots aren’t able to absorb nutrients like before since they are getting old.

This means that fungus might show up on top of soil or even near the base if it grows from rotting roots due to over-watering.

If this happens, it’s best to repot the cactus plant into a bigger container with more drainage and better soil quality!

Fungus Diseases

Some fungus diseases can occur on plants like powdery mildew or botrytis, which typically grow from overwatering.

For these conditions, you will see leaves begin to turn brown and curl up at the top of your plant where there isn’t any green color left instead of just white mold growing on top of soil or near the base.

In cases like this, immediately remove all affected areas so that they don’t spread – do not water for two weeks either since fungal spores could still be inside new parts without showing signs of it yet.

Types of Cactus Fungus

Different types of fungus can affect cactus plants. These include:

Powdery Mildew

The cactus leaves may turn yellow or brown, and its growth will be stunted if left untreated.

Powdery mildew is caused by fungi in the family Erysiphaceae, which produce powdery white spores on the surface of foliage, flowers, stems, and even fruit.

These spores spread via wind or rain splash to infect other plants nearby.

This fungus does not require free water (such as dew) for germination, but it needs humidity levels above 75 percent to grow well.

Downy Mildew

This fungus will cause the leaves to develop yellow spots.

Eventually, these areas become covered with a fine downy growth of white fungal growth, which can be seen in the early stages when viewed from a short distance.

The cactus plant may also have black lesions on its side if infected by Phomopsis leptostromiformis or gloeosporioides fungi species that produce reddish spores and greenish-grey pustules, respectively.

Leaf Spot

This fungus causes dark spots to appear on the cactus plant’s leaves which become significant brown areas with a white or greyish center.

These spots may also have purple or brown borders and increase in size as the fungal disease progresses.

The cactus plant will become bleached and distorted if this fungus is left untreated.

Rust Fungus

Rust fungus causes orange or yellowish bumps to appear on the surfaces of cactus plants’ leaves and branches.

It is caused by fungi species from the genus Puccinia that spread through windblown spores, rain splash, insects, animals, garden tools, and clothing brought into contact with the plant.

Cactus Root Rot

This fungus causes cacti to develop brown patches on their roots, often surrounded by a yellow halo.

It is caused by fungi species in the genus Phytophthora that spread through spores carried into the soil via wind, rain splash, or garden tools brought into contact with infected plants.


These fungi produce pinkish spores, and their infection results in tiny circular, angular, oval, lobed, or irregularly shaped lesions on both sides of the leaf blades.

As this disease advances, it can lead to defoliation of parts of plants that are most severely infected by causing premature loss of foliage and stem damage due to girdling caused by fungal growth around vascular bundles near crotches at branch/stem junctions.

How To Get Rid of Fungus on Cactus Plants

Fungus on cactus plants can be annoying. However, there are several methods you can use to get rid of fungus on cactus plants.

Method #1: Cut Off The Infected Area

First, cut off any areas of fungus on cactus plants using a sterile knife or clippers.

Then spray those healthy parts with a fungicide once every two weeks for six to twelve months, depending upon which fungicide you use.

To promote growth and prevent future outbreaks of disease, fertilize your plant as needed according to the instructions on the package.

Also, make sure that it remains evenly watered throughout this period as well– try not to let it dry out entirely between waterings because too much moisture may cause root rot problems in addition to black spots!

Method #2: Use Baking Soda and Hydrogen Peroxide

One of the most common methods is to make a baking soda (sodium bicarbonate) solution.

Mix two teaspoons with one quart of lukewarm water and pour it into an empty spray bottle.

Spray your cactus plants thoroughly until they are wet, including the undersides and tops of leaves, whenever you see signs or symptoms such as leaf spot that indicates fungus on cactus plants has begun its attack again.

You should do this at least twice per week for six weeks straight to get rid of fungus on cactus plants once and for all!

Method #3: Make Your Own Fungicide Solution

Another effective method involves making your own fungicide solution.

Mix one tablespoon of baking soda, hydrogen peroxide, and liquid soap with a gallon of water in an empty spray bottle.

Spray it liberally onto your cactus plants every two weeks for at least six months to get rid of fungus on cactus plants completely!

Method #4: Spray With White Vinegar Solution

A third option is to mix one part white vinegar (or apple cider vinegar) with four parts water into an empty plastic container or bucket, then dip the leaves into this solution carefully until they are thoroughly saturated but not dripping wet.

Let them air dry without rinsing off any remaining fungicide that has stuck on the surface because less than half will be removed when you rinse so much better just to leave it there!

If you make this solution yourself, it should be used within a week. If you buy it, make sure to store it in a cool, dry place.

Method #5: Clean Your Cactus Plant Thoroughly With Soap and Water

The most basic way is simply by cleaning your cactus plant thoroughly with soap and water daily or every other day at least– especially after working around them when they are dusty!

Dust acts as an insulator protecting fungi from drying out, so be sure to wipe off any dust before spraying fungicide according to method number three above.

This should also help prevent future outbreaks of fungus on cactus plants too!

Just spray down all leaves, including undersides, using one tablespoon each of baking soda, hydrogen peroxide, and liquid soap mixed into two quarts of lukewarm water.

Method #6: Use a Fungicide Solution

When your cactus plant becomes infested with fungus on cactus plants, you can use fungicides.

There are different types of fungicides available– some work better than others, and they all have specific purposes, so make sure to choose the right one for what you need!

Remember that even if just one or two leaves show symptoms, it’s important to spray them down because otherwise, this disease will spread quickly throughout the entire plant in no time at all unless treated aggressively from the early stages.

How To Prevent Fungus in Cactus

To prevent fungus on cactus, you need to follow the following tips.

  • Make sure that your plant is in a sunny location with well-draining soil.
  • Water only when the top inch or two gets dry, and always use room temperature rainwater if possible.
  • Do not overwater your cactus plants.
  • Provide proper drainage in pots so that soil stays dry, especially when you are growing them indoors. This is very important to avoid fungus on cacti.
  • Do not keep your cactus wet for long.
  • Remove diseased and damaged parts of the plant immediately to prevent fungus from spreading.
  • Always sterilize your tools before and after you use them to repot plants.
  • Do not touch the plant with bare hands. Instead, wear gloves when working with cactus soil or potting mix. This will prevent fungus on cacti from spreading through your skin.

Final Thoughts

Fungus on cactus plants is a common problem.

Many people choose to use organic methods of treatment, but this is not always the best solution.

If you treat your plants with fungicides and other chemicals regularly, they may become resistant to these treatments in future problems.

It would be better if you used an integrated approach that combined chemical and organic solutions together- what works for some fungi might not work for others.

It would also be a good idea to prevent fungal infections from happening in the future by creating an environment that is less friendly to fungus.

You can do this by placing your cactus plants in a more sunny environment as some types of fungus prefer to grow on damp and shady surfaces.

In addition, you should also make sure that the soil around your cactus is very well-drained, so they don’t stay wet for too long.

If you follow these steps, you should be able to treat your fungus on cactus plants successfully!

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