Skip to Content

How to Get Rid of Brown Spots on Cactus (And Prevention)

Have you noticed any brown spots on your cactus lately? Probably because it’s a problem that many people have with cacti, and those problems can be quite alarming. Cactus is known for its toughness, but it can be vulnerable at times.

The brown spots on the cactus are caused by changes in physiological processes. It can be caused by changing environmental conditions (light, humidity, temperature, frost, and poor air circulation), mismanagement (overwatering, overfertilization), and biotic factors (pests, fungal diseases).

To understand why brown spots appear in your cactus, it’s critical to know the mechanism behind its causes.

This article will help you better combat the problems that in turn minimize the chance of your cactus acquiring brown spots.

How to Identify Cactus Brown Spots?

Brown spots may look different depending on what caused them, how long they’ve been there, and how bad the damage was.

They differ in size, brown color shade, and even texture. Some of them dry up and look like lesions, while others form blisters.

Why Does My Cactus Have a Brown Spot?

Excess Sun Exposure

To keep their vibrant hues, cacti require a lot of bright light. Light is also required for photosynthesis, which produces food and supports physiological functions.

Now, overexposure to the sun can result in scorching and brown spots on your cactus.

Excessive sun exposure activates the cactus’ defense mechanism. It produces anthocyanin, a pigment that causes the color to turn purple. This color change indicates a state of stress.

Before exposing your cactus to direct sunlight, make sure to acclimate it. This procedure must be carried out gradually.

Sunburnt Cactus
Sunburnt Cactus

1. Move Your Plant Indoors

Bring your plant inside if it’s outside. Your cactus is having a hard time dealing with the excess light. Extreme light exposure can be minimized by bringing it inside your home.

2. Provide Additional Shade

When the light intensity inside is too high, the result can be scalding. To reduce the intensity, you’ll need to provide the plant with additional shade.

You can do this using curtains or larger plants to block some of the light.

Improper Watering

Brown Mushy Spots Due to Overwatering
Brown Mushy Spots Due to Overwatering

Overwatering or underwatering are both examples of improper watering.

Cacti can withstand drought conditions, so lack of water isn’t a big deal. You need to be careful not to use too much water.

Factors such as potting mix quality, watering frequency temperature, and humidity all affect water use.

You’ll end up drowning your cactus if you’re not careful. This allows root rot to occur.

Brown, mushy spots on the roots are a telltale sign of root rot.

These spots are the plant’s rotting parts that have begun to decay.

This is because the roots have been damaged and are no longer able to transport nutrients and water.

Check How Moist the Soil Is

You can tell if the soil is overwatered by dipping your finger at least an inch below the surface. Also, make sure you are using a good drainage capacity soil for cactus.

Soggy soil is a sign that it has received too much water. Soil that’s dry to the touch is ideal for cacti and succulents.

Temperature Stress Can Damage the Cells

High and low-temperature fluctuations stress your cactus. Sudden temperature changes are not recommended for your cacti because they will shock the plant. 

The ideal temperature is between 45 °F and 85 °F (7-29 °C). Your cacti’s tissues can be damaged by extremes of temperature.

The outcome is frequently quick. Because of this, you’ll be able to see the damage, such as brown spots, within a short period of time.

1. Relocate the Cacti Pots

You should be careful if your cacti pot is near a window, as the glass may be causing your plants to overheat or overcold themselves.

Moving to a place where the temperature is more stable can help alleviate the effects of temperature stress.

2. Provide Insulation When Cold

Insulating your cactus is an important step in protecting it. Evening temperatures are generally cooler, but when the winter months arrive, they can plummet even lower.

Giving the plant some extra warmth will aid it in dealing with the sudden drop in temperature.

Pest Infestation Causing Spots on Cactus

Scale Insect on Cactus
Scale Insect on Cactus (White Dots)

Although I rarely see pests infecting our cacti, you can’t rule out the possibility that they’re to blame for the brown spots on our plants.

Pests typically infect cacti by sucking on plant tissues. As a result, the cactus’ surface is scarred by small wounds that eventually turn brown.

Armored scales (Diaspididae), which feed on plant fluids with their straw-like mouthparts, are an example of one of these pests.

Because they are so small, they can be difficult to detect. So, you may not notice them until the plant begins to show signs of the harm they’ve done.

Mites are also a threat. If they manage to multiply, they will cause damage to the plant, turning infected parts yellow or reddish-brown. (Source: University of California)

Inspect the Cacti for Any Presence of Pests

Because these organisms are too small to be noticed by the naked eye, you must make an effort to check your cacti for stray insects.

Once in a while, you can use this method to stop the spread of disease. Check all of your indoor plants to see if the pests haven’t made a new home elsewhere.

Fungal Disease 

Brown Spots on Cactus Because of Fungal Attack
Brown Spots on Cactus Because of Fungal Attack

Fungi and other pathogens can cause disease on your cactus. It can be extremely difficult to eradicate an infection once it has taken hold.

Cactus are permanently damaged by Colletotrichum (Gleosporium) spp. the most common fungus for cactus anthracnose.

First, the infected area appears moist and light brown. Over time, the spots spread to cover the entire plant. Cacti plants infected with fungal diseases are at a much higher risk of dying.

1. Discard Infected Portions

To prevent the spread of the disease, it is best to immediately cut off the infected portions and properly dispose of them.

There may even be times when you must dispose of the entire plant. Anthracnose is difficult to control.

2. Apply Fungicide

Chemical control is a quick fix for the fungal problem. Fungicides can be either preventive or curative in nature. 

Preventive fungicides should be used before planting, and curative fungicides should be used once symptoms appear.

3. Avoid Humid Conditions

Pathogens, such as fungi, thrive in moist environments. There is a high risk of developing fungal diseases if the moisture level is high.

Cactus does not like high humidity, so you must keep the environment in check.

Rust Spots on Cactus

Rust Spots on Cactus
Rust Spots on Cactus

Rust is one of the diseases that can develop in cacti, particularly the cactus pear. Puccinia opuntiae, a type of fungus, is to blame.

This fungus, according to FAO, “produces yellow-orange pustules on the surface of cladodes or fruits” of the cactus. (Source)

When the rust spot dries, you’ll notice a hole. The infection site will spread until the plant is severely infected. Failure to intervene may result in the death of the entire plant.

1. Remove and Bury the Infected Clalode

This is the most recommended method for dealing with cactus rust disease. Once you notice the symptoms, you must remove the infection sites as soon as possible to prevent the disease spread.

2. Isolate the Infected Plant

Plant diseases spread like wildfire. Other plants are at risk of becoming infected if you are not cautious. Isolating the plant will aid in disease control.

3. Apply Preventive Fungicide on Other Cacti

If you have other cacti that haven’t been infected, you should protect them by spraying them with fungicide.

It’s a good thing because the market already offers organic and inorganic options.

Just be careful when you use fungicides and always follow the directions on the labels that come with them.

Fertilizer Overdose Can Burn the Cactus

Cacti aren’t heavy feeders, so they don’t need to be fertilized all the time. If you’ve overfed the plant, you’ll likely see brown spots on the stems as a sign of damage. Adding too much fertilizer will cause the cacti’s tissues to burn.

Salts can also accumulate in the soil as a result of over-fertilizing. These salts alter the soil’s pH and reduce its population of beneficial microorganisms.

Roots can also become damaged and stop working correctly. The cactus will turn brown as a result.

1. Leach Or Rinse Off Excess Fertilizer

You can quickly fix the excess fertilizer by leaching it off using water. Thoroughly pour in water in the pot until it drenches. Wait for a few hours and do it once again. 

2. If Necessary, Repot in Fresh Potting Soil

To avoid overfertilization, it is sometimes necessary to repot a cactus.

If leaching isn’t enough, you’ll need to prepare new soil for repotting the plant. Before putting it in the soil, inspect the roots for any signs of damage and trim them if necessary.

Inadequate Air Circulation

Poor air circulation is a common issue in an enclosed indoor setting. A lack of good airflow will prolong the damp condition, especially if you’ve recently watered your plants. We already know that a moist environment invites pathogens to grow.

1. Open the Windows and Doors

You can encourage air circulation by opening the windows and doors for a few hours. Not only will it benefit the plant’s health, but it will also benefit you. By allowing in fresh air from the outside, you are forcing the air inside to circulate.

Allow your cacti to breathe in some fresh air outside. Place it in an open area with plenty of light. It will aid in the evaporation of excess moisture from your cacti.

2. Make use of the Exhaust Fan

Exhaust fans work by removing fumes, odors, and moisture from the inside of your home and venting them to the outside.

It aids in the promotion of air circulation in a given area. Fresh air can now enter the room after the stuck air is pulled outside.

High Humidity Triggers Fungal Growth

Cactus grows best in dry, arid environments like deserts. When the humidity level in the air is high, cacti are prone to rotting.

High humidity combined with overwatering is responsible for a number of deaths. Pathogen growth is also accelerated. These unfavorable conditions will harm the health of your cacti.

What to Do?

Avoid humid areas of your home, such as kitchens and bathrooms, as these are the most humid.

You can skip the watering schedule if the environment is extremely humid. Because of the moisture in the air, transpiration will undoubtedly be slow.

If you add water to the soil, your cacti will struggle to absorb it, resulting in overwatering.

Frost Damage

Cacti are not frost-hardy. During the winter months, they are particularly vulnerable to damage from freezing temperatures.

As a result of their high internal moisture content, they are susceptible to freezing at extremely low temperatures. There will be brown spots on different parts of the plant as it thaws out.

1. Relocate the Cacti During the Night

The nighttime temperature is lower than the daytime temperature.

The nighttime chill will undoubtedly affect the plant if it is located near a window glass. If that’s the case, you’ll need to relocate it to a more hospitable location.

2. Protect the Cactus Plant by Keeping It Warm

Covering cacti with cotton sheets is an option when temperatures are cooler. It will keep the plant from freezing by creating a warm environment around it. How thick the insulation should be will depend on how cold it is outside, so make sure it’s thick enough.

3. Warm the Area Up with Lighting

Your cacti benefit from additional warmth provided by artificial light. During winter, you can group your plants together and install a 100-watt lamp above them. Make sure there is enough room for the lamp, and don’t let it touch the sheet cover.

How to Prevent Brown Spots on Cactus? 

Start with Disease-Free Cacti

Always choose a healthy and vigorous cacti whenever you buy. Inspect for any presence of brown spots and if you see any, don’t make a purchase. Starting with healthy plants will save you a huge amount of work.  

Use Clean and Good Quality Potting Soil

The kind of potting mix that you use is very important for the success of your cactus plant.

If you’re unsure of how to do the right mixture, make use of the readily available cacti mixes in garden stores. What’s important is that it’s sterilized (pathogen-free) and is well-draining. 

Find the Best Location

It has to be well-lit, relatively less humid, and warmer. Those conditions are ideal for your cacti to thrive.

There are times when these conditions drastically change so you have to pull a few tricks like using exhaust fans, artificial light sources, etc. 

Regulate Water and Fertilizer

Cacti won’t need so much of these two inputs. It’s better to give them in regulated amounts than overdo it. Any excess will take a toll on the health of your cactus. 

Use Fungicide as Preventive Measure

You can apply fungicide to the soil to prevent the growth of fungi. This will help eliminate the chance of developing fungal diseases.

You can make use of baking soda as a natural fungicide or commercially available organic and inorganic fungicides.

Check and Remove Pests Regularly

Visit your cacti regularly and inspect for any present foreign organisms. If you’re early to spot them, you can prevent them from bringing further damage.

There are many ways to control pests such as mechanical, chemical, biological, and physical methods.

FAQs

How Do I Get Rid Of Black Spots on My Cactus?

Black spots on cactus appear as a result of undergoing stressful conditions brought about by abiotic or biotic factors.

There are different possible reasons why your cactus is having black spots. The first thing you need to do is find the exact cause. The treatments for black spots vary depending on what causes them.

Abiotic factors such as excess light, overwatering, over-fertilizing, high humidity, and cold temperatures can be managed by applying simple techniques. If the problem is caused by pathogens, it will be more challenging. 

Can You Revive A Brown Cactus?

It depends on the extent of browning. If the majority of the cactus body is already brown, you might as well let it go. It would be difficult to try to save an already lost cause. 

However, if the browning is somewhat minimal, you can still save the plant. Investigate how the cacti respond to the treatments you’ve applied. If the browning lessens, you’re on the right track. 

What Does An Overwatered Cactus Look Like?

An overwatered cactus would have brown portions that are mushy when touched.

The roots are damaged and the base of the plant is usually rotten and weak. When you try to pull it out from the soil, the base would easily detach from the roots. 

The appearance of brown spots on the cactus indicates an internal problem. It’s a sign that you must not ignore. Otherwise, you’d be too late to notice the damage. 

Final Words

In keeping your cacti healthy, prevention is still the best way. Keep in mind the basic growing conditions that it needs and try to stick to it as much as possible. Be quick to determine environmental changes and make adjustments if necessary.