Why Is My Cactus Has Spots?

Are you observing brown spots appearing on your favorite cactus? Well, it is one of the common problems that you might encounter with your favorite cacti. However, simply because it is common doesn’t mean it can be ignored. Brown spots appear due to various physiological imbalances and are most likely going to damage your cactus. Thus, immediate steps need to be taken to ensure that your cactus is not damaged by these brown spots.

Causes for pots appearing on Cactus

Let us discuss some of the common reasons which cause brown spots in these cactus plants-

  • Temperature Fluctuations
  • Excess Watering
  • Pests and Fungus

1. Temperature Fluctuations

Both sunburn and freeze injury may occur if your cactus is exposed to extreme fluctuations in temperature. It generally happens when the cactus is left outdoors or near sources of extreme heat or cold. The spots are initially black and eventually turns brown as the plant starts to die. While the coloration is permanent, such damage only tends to be cosmetic.


Bring the plant indoors if there are extreme fluctuations in temperature, such as a very sunny day or a freezing night. Similarly, avoid placing your cactus near sources that radiate heat or cold , such as refrigerators and air-conditioners. If you have placed your cactus near a window that receives direct, amplified sunlight, shift it to a location where it receives abundant but indirect heat.

2. Excess Watering

The quality of potting, watering frequency, and humidity are some of the factors which determine the amount of water a cactus needs. Since it is very easy to be over-enthusiastic about your cactus and over-water it, you need to be careful about the amount of water you give your favorite plant . It drowns and weakens your cactus, eventually making it susceptible to infections such as root rot which causes brown spots to appear in the plant.


Root rot can be very dangerous to your cactus, so always keep an eye out for any signs of browning. If any symptoms are spotted, immediately severe the rotten parts of the plant to save it. Then, spray the plant with an effective fungicide until the plant heals and use sterile soil to re-pot the plant after it has recovered from the infection.

3. Pests and Fungus

Certain pests like armored scale can be fatal to your cacti. These are tiny bugs that are generally covered in a waxy protective substance which makes them hard to kill. They tend to such on the juices of the plant and leave scars that turn into brown spots.

Similarly, fungal infections such as anthracnose and root rust cause the plant to develop moist, brown spots, which eventually become enlarged. These are very serious diseases, and if left unchecked, can often destroy the cactus.


Pests like armored scale are very hard to get rid of or contain. So, if you detect these bugs immediately quarantine your cactus. The most effective method of removal is to use a cotton swab dipped in rubbing alcohol and apply it to the affected area. However, since this method is very time-consuming, you can also spray an effective insecticide or a diluted solution of rubbing alcohol.

Similarly, in the case of fungal infections, quarantine the plant, reduce watering, and coat the plant with neem oil every week until the infection is gone. You can also remove the plant from humid environments to reduce the chances of re-infection.

Thus, these are a few methods to help your cactus if it tends to start developing spots.

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