Why Does My Cactus Have White Spots? [What To Do]

The humble cactus is one of the best houseplants for busy plant lovers. They need little maintenance, and they can survive without too much watering and fertilization.

However, they have come with their own set of problems. One such issue is the development of white spots. Let’s look at why cacti develop these white spots and what you can do about them.

Table of Contents

Why Does My Cactus Have White Spots?

Pest Infestation

Scales and mealybugs are two distinct pests threatening the health and integrity of indoor cacti. Most plant owners ignore the white cotton-like substance on their cacti and often mistake it for mold.

However, what they might not know is that the white substance is a protective shield for scales to hide. Scales are brown in color, and they are shrouded in white fluff.

Scales feed off the sap that dries the cacti, thus resulting in white spots. On the other hand, Mealybugs are small, slow-moving pests hiding under white fuzz.

Mealybugs don’t live for more than 10 weeks. Their eggs take approximately five weeks to incubate before turning into nymphs.

From the sixth week, the nymphs start to grow and turn into full-grown adults. Their short lifespan is the reason they can multiply quickly.

Mealybugs feed on the foliage, which results in yellow leaves, twisted foliage, and white spots.

Fungus

Fungal growth in cacti is rare, but it is possible. It happens when the cactus is placed in wet and humid conditions. The area under the fugal region is soft to the touch, which is how you can identify it.

These white spots won’t kill your cactus, but they result in stunted growth, deformed foliage, and yellowing.

Besides shielding the pests, the white fuzz can also be a powdery mildew because it thrives in similar environments.

As the fungal growth spreads, the plant starts deforming, and the foliage turns pale yellow. Another reason behind white spots on cacti is the impatiens necrotic spot virus, also known as white rot.

How to Get Rid of Pest-Inflicted White Spots in Cacti

Mealybugs aren’t picky eaters, and they start to munch on whatever plants they can get their teeth on. If your cactus has mealybugs, the first thing you need to do is quarantine the plant.

After quarantining the infected cactus, spray some neem oil on the rest of the plants to prevent the spread of the infection.

If the infection spreads fast, consider repotting your cactus. Doing this reduces the number of pests on your cactus, and it will be easier for you to remove them with tweezers or the chemical remedies we will discuss.

Isopropyl Alcohol

Dip a small rag or cotton ball in isopropyl alcohol and dab it on the visible pests. The process may take time, but it sure is effective.

Also, don’t forget to inspect the hidden sides of your cactus. These areas include the undersides of the leaves and the leaf joints.

Mealybugs can also thrive in potting soil. Make sure to remove the upper layer of your potting soil to remove any mealybugs hiding within.

The roots also catch pests. If this is the case, wash the roots with lukewarm water, and dip them in a pesticide. Also, pay close attention to the bottom and the sides of the pot, as pests can cling to it easily.

The isopropyl alcohol treatment must continue every day for one week. Any irregularities in the schedule may result in the regeneration of pests.

Make sure to try isopropyl alcohol on a small area. Don’t apply too much alcohol to the entire plant, or you will end up damaging the plant.

Make a DIY Insecticide

If you don’t find the alcohol method effective or find it too time-consuming, you can prepare your own insecticide.

Pour a teaspoon of dishwashing liquid into one cup of water and mix. Take your plant to the sink of the shower area.

Rinse the white spots with your DIY insecticide and wash the plant with cold water. Water shouldn’t be left sitting on the foliage. Make sure to dry your plant before taking it to a bug-free location.

The treatment should be repeated for three-four days in a row. If you still find mealybugs or scales on your cactus, you can use a small amount of isopropyl alcohol.

Inspect the plant daily, as some pests hide in leaf joints. If the DIY insecticide doesn’t work on its own, prepare a mixture of alcohol, neem oil, and your DIY soapy insecticide, and apply it to the white spots.

Also, wash your gardening tools and equipment, and they too can harbor pests. You can also use nature’s pesticide to get rid of mealybugs and scales on your cactus. Of course, we’re talking about ladybugs and lacewings.

However, ladybugs and lacewings are helpful only till the pest infestation is negligible. If pest infestation has gotten out of hand, you must return to your alcohol mixture.

How to Eliminate Fungus-Inflicted White Spots

Start by removing the areas infected by fungus. Mix one part milk into three parts of water, and spray the concoction onto the white spots with a spray bottle.

Initially, spray your cactus with the milk and water mixture regularly for two to three days. Then, take a break and repeat the same method after 14 days.

What If Pests Keep Reappearing

It is common for pests to reappear even after all the treatments we have discussed above. This happens when you leave a hidden area on your cactus. Here is what you need to do.

Replace the top one inch of your potting soil with fresh soil.
Try relocating your cactus to a different location, as the current location might be triggering the reappearance of pests.

Frequently Asked Questions

How Long Should You Quarantine Your Cactus?

After treating your cactus with various cleaning products, make sure to quarantine it for at least three weeks. It will help you identify the bugs much quicker if they were the ones causing white spots in the first place.

Should You Sterilize the Pot After Treating Your Cactus?

If your cactus pot is made of terracotta, you must sterilize it after treating your cactus. Terracotta is a porous material that serves as a breeding ground for eggs. To sterilize the pot, all you need is some bleach and water.

How Do You Know If Pests Are Causing White Spots?

Take a gardening tool and scrape away the white fuzzy material on your cactus. Be gentle or you’ll end up damaging the foliage. Then, squeeze the fuzz, and if it secretes a red substance, you’re dealing with a pest infestation.

Final Word

Longer-lasting houseplants like cacti are suitable for plant lovers who don’t have too much time to maintain their plants. While cacti may not need regular maintenance, watering, or fertilization, they can develop pest infestations and fungal infections.

As a plant owner, you must be vigilant enough to spot the white spots caused by pests and fungus. Before using any of the remedies mentioned above, make sure to quarantine the infected cacti so the infestation doesn’t spread to other plants.

Lastly, don’t forget to cleanse and sterilize the pots and the gardening tools used to treat your cactus, as they can harbor enough pests that damage other plants.