Why Is My Cactus Turning Black? Diseases of the cactus and how to cure them

The cactus plant is available in a variety of hues, ranging from basic green to vibrant tones of orange, pink, red, and yellow. However, if your cactus starts to turn black, it’s generally a sign that something is wrong.

So, what’s the deal with my cactus becoming black? Fungal diseases including bacterial necrosis, crown rot, and phyllosticta pad spotting are commonly to blame for a blackened cactus. In this essay, I’ll discuss the most prevalent causes of a cactus houseplant going black, how to treat it, and what causes cactus fungus.

It’s time to get down to business and address that all-important question: ‘Why is my cactus becoming black?’

On a cactus, what produces fungus?

First and foremost. A fungal infection is most certainly causing your cactus to become black. It may appear moldy, or it may simply be beginning to blacken at the top. This is very uncommon, though, as most plant species are susceptible to mold or fungal infections.

So, what causes cactus fungus? Your cactus’ fungal problem is caused by a variety of factors. Fungal organisms are abundant, with millions of distinct varieties, the majority of which can survive by becoming dormant for extended periods of time. The most essential thing to remember is how to manage fungal illnesses, not the sort of fungus disease your indoor cactus has. In this manner, if your cactus starts to turn black, you’ll be well-prepared.

Opuntia, Agave, and Saguaro are the most prevalent varieties of cactus that are susceptible to fungal diseases. However, these diseases may affect almost any species of cactus, so it’s not uncommon to wonder why yours is becoming black.

Cactus infections come in a variety of forms

Before we start fungal therapy for cactus, it’s important to first understand the many forms of cactus infections. As previously said, if you’re wondering why your cactus is going black, it’s most likely due to a disease.

We couldn’t cover all of the fungal organisms that can infect a cactus plant since there are so many. Bacterial necrosis, crown rot, and phyllosticta pad spotting are the three most prevalent illnesses that cause a cactus to blacken.

Bacterial Necrosis is a disease caused by bacteria

What is bacterial necrosis, and how does it happen? Bacterial necrosis is a fungal disease that affects the saguaro cactus. It’s a very basic illness that rots the plant’s tissue and, if left untreated, may be both stinky and life-threatening for the saguaro cactus.

A blackened area on a saguaro cactus that might smell and feel soft is the first evidence of bacterial necrosis. It will eventually lead to black lesions that emit an odorous fluid and necrotic areas that will spread. Necrotic pockets are dead plant tissue that will destroy your cactus if left untreated. Your saguaro cactus has an 80% chance of surviving if caught early enough.

You’ll also note that the necrosis of the saguaro cactus produces a corky area. This is the plant’s attempt to mend itself, but any break in the corked region may release the bacteria, infecting your plant more. The area with the corky appearance will be darkened.

Bacterial necrosis may only be treated by physically removing the affected region with a clean, sharp, sterilized knife. However, because germs may thrive in the soil or ground, your cactus plant may not be completely saved.

Crown Rot is a disease that affects the crown

What exactly is crown rot? Crown rot is a kind of soil-borne fungus that grows in damp, heavy soil. Cactuses benefit from fast-drying, airy soil, but this does not guarantee your plant is immune to the fungal illness. Crown rot may harm practically any plant, shrub, tree, or vegetable patch, therefore it’s crucial to understand the basics of this disease if you’re a gardener.

The first evidence of crown rot on a cactus is on the soil, and it looks like dry rot. Other symptoms may go missed until the afflicted regions become black, tan, or brown in color. It’s typically too late to salvage your houseplant at this point. This is why crown rot is so lethal: you may not even realize your plant has it until it’s too late.

It’s quite tough to get rid of the fungus once it’s in the soil

What is the best way to cure crown rot? Crown rot is difficult to reverse after it has progressed to the point where your cactus is blackened. Fungicides, together with adequate watering, can help avoid illnesses; nevertheless, once the disease has taken root, it is difficult to eliminate for good. As previously said, crown rot begins in the soil, therefore consider repotting a cactus and refilling the soil.

Pad Spotting in Phyllosticta

What is phyllosticta pad spotting, and how does it happen? Prickly pear leaf spot, also known as Phyllosticta pad spotting, is a fungal disease that affects prickly pear cactus and other members of the Opuntia family. The phyllosticta fungus colonizes the pads of a cactus and causes sores with its tiny spores.

If your cactus plant has phyllosticta pad spotting, you should remove it from any other plants you own right once, since the illness can spread quickly. To prevent the illness from spreading further, gently remove the affected pads from your prickly pear cactus.

Fortunately, this fungal illness just causes aesthetic damage to your cactus plant and will not kill it. Phyllosticta concava, often known as dry rot, is the most prevalent cause of prickly pears.

Black circular lesions ranging in size from 1 to 2 inches in diameter are one of the initial indications of phyllosticta pad spotting. These dark hues are produced by reproductive structures called pycnidia, which release spores; if circumstances change, the spots will fall out of the cactus, leaving a scar.

Because this is a weather-dependent illness, your cactus will not suffer long-term or major harm if the weather returns to being warm and dry.

Learn More About Caring For Cactus Plants

How do you cure a cactus with black fungus?

So, you’ve found the answer to the age-old query, “Why is my cactus becoming black?” Hopefully, it will be one of the three fungal infections listed above.

But how can you cure a cactus with black fungus? It usually relies on the severity of the harm. If your cactus starts to turn black in the early stages, a simple cactus fungus treatment/fungicide spray can help.

If, on the other hand, the fungal lesions cover a significant area, it’s preferable to start anew with cuttings. To start a new plant from cuttings, cut away at the healthy sections of the cactus using a sterilized knife.

If you aren’t ready to let go of your beloved cactus and the lesions aren’t completely covering the plant, you can try to salvage it by chipping away at the affected portions. This isn’t effective against many fungi, such as crown rot, but it could be for others.

You should remove more tissue than looks to be contaminated to ensure that all infected regions have been eliminated. Maintain a dry environment for the plant and keep an eye out for reinfection!

What is causing my cactus to rot?

The major reason your cactus is reverting back (rotting) is most likely due to fungal illness, as we’ve already stated. But what causes cactus fungus? Overwatering is a common cause, especially if the cactus is decaying from the bottom up. If you overwater your cactus, it will initially become mushy and spongy.

Cacti thrive in low-moisture situations in general. A cactus thrives at temperatures between 70 and 75 degrees Fahrenheit, in a bright, sunny location (preferably a south-facing window if you have an indoor plant), and requires very little supplementary nutrition.

You should only water your cactus when it is absolutely necessary to avoid decay. Before rewatering, make sure the soil is completely dry. If you have an indoor cactus in a pot, make sure it has drainage holes. If you don’t, your cactus may wind up resting in water, with wet roots, resulting in root rot and fungal illnesses.

Cactus with black dots

So you’ve read this article and are confident it’s not a fungal ailment that’s causing your cactus to turn black. We’ve talked about cactus lesions and how they might appear, but you could be right if you think your black spots on cacti are caused by something else!

Another reason you could see black patches on a cactus is because of temperature shock. Cactus species thrive in hot climates, as we all know. Succulents are desert plants that can survive with very little water. Cacti, despite their ability to adapt to a variety of temperatures both indoors and out, do not do well when the temperature drops suddenly.

There will be apparent changes to your gorgeous plant in really cold conditions, even if just exposed for a few hours – one of them being black patches on a cactus that seems damp at first.

The black areas will become dry and brittle after drying, and they may even fall off – a serious case of frostbite! This is frequently related to tissue damage caused by cold weather.

Fortunately, freezing temperature damage is unlikely to be substantial, and your cactus plant will be able to restore the destroyed tissue.

The black patches will go away and the area will return to normal. Just make sure you don’t make the mistake of letting your cactus out in the cold! If you live in a cold climate and have an outdoor cactus, you might consider bringing it within for the winter.

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