Most cacti are green, but they can get white spots for an unknown cause. Should you worry? It sometimes happens quite often, even in my garden, so I tracked down several reasons for this problem and how to fix it.
Cactus develop white spots because of 1) pest infestation, 2) lack of light, 3) extreme sun exposure, 4) natural characteristics, and 5) fungal growth. Pests and fungi are eliminated using pesticides and fungicides, and sunlight problems are solved by adjusting light exposures.
Several troubles could arise in the garden over time, and cacti plants are not spared from any of these despite being known as tough plants. One common cacti problem is when they develop white spots in their stem. Stick around if you want to know why cacti get white.
Cacti may develop white portions on their stem all of a sudden. It is crucial to assess the situation immediately to administer the needed solution and save the plant. Below are the possible reasons cacti get white and the best way to fix them.
Most of the time, white spots on cacti are due to pests and insects. The common ones are mealybugs and scales that attach their bodies to the cacti stem and feed on the plant’s sap. Mealybugs appear like fuzzy white cotton, while scale insects appear as white waxy bumps on the cacti’s epidermis.
Mealybugs can cause your cacti to develop white spots as the female lays eggs and builds colonies. They hatch the eggs inside a cottony white sac sticking on the nooks and crannies of the cacti stem. As the mealybugs multiply, they invade the entire cacti making colonies of white clusters.
Likewise, scale insect infestations appear as white waxy flat spots on the cacti stem. Scales are like tiny white dots with a brown center. The whitish outer layer is the protective shield from their predators and the destructive effect of pesticides. Although they are not fatal, they can spread rapidly.
If you notice any of these signs, then pests are the cause of white spots on your cacti. Read more below on how to eliminate them.
White spots on cacti caused by pests can be solved through 1) manual removal, 2) dabbing with alcohol, 3) spraying with DIY pesticide, and 4) treating with organic neem solution. But before doing these remedies, it is crucial to separate the infected plant away from the healthy ones.
Pests reproduce quickly, and the next time you check, they are all over your beloved cacti. So what I always do is control them before they get any worse and kill my plants. I use different remedies when dealing with pests, and I will discuss how.
1. Manual Removal – This method is only suitable for early and small infestation. Here, I use a tweezer and hand-pick every harmful insect I can see on the cacti. I scrape them off and destroy their colonies.
2. Dabbing With Alcohol – With a q-tip soaked with 70% alcohol, dab it on the visible pests. Check also the under spines and ribs for hidden colonies, and likewise, do the dabbing process. This requires a lot of time, but it kills the pests right on the spot due to direct contact with alcohol.
3. Spraying With DIY Insecticide – DIY Homemade insecticide solution using an oil-based soap and water is a safe way of killing pests effectively. Make a 2% soap solution and spray it directly to the white clusters of colonies to completely destroy them.
You can find an oil-based soap online just like the one below.
4. Treating With Organic Neem Oil Solution – I use an organic neem oil mixed with water in a 2% solution if it is a massive infestation. Neem solution application can be sprayed directly and thoroughly into the infestation to reach every single pest alive. Here is an excellent neem oil concentrate.
Not enough sunlight can make a cactus tissue turn white on a large area. This discoloration develops from its top. An extended period without the proper sunlight can lead to pale or whitened cacti tips that are stretchy and thin. It will cause cacti to lose their original shape.
The appearance of the white portion is not spotty but extends from the top area going downwards. Cacti tissues start to turn white from the crown and expand as the cacti grow in the absence of light.
As the cacti grow with insufficient light, the tissues they produce lack green chlorophyll leading to whitened tips. These light-deprived stems become elongated as they find their way to reach for more light. When your cacti are deformed and get white from the top, it lacks sunlight.
Cacti that became white due to inadequate sunlight can be fixed by transferring the plant to an area with more light. A balcony, window sill, under the tree, or inside a greenhouse is the best place where cacti can receive ample sunlight.
Indoor cacti are likely to turn white due to a lack of light. So to make them green again, you can bring the cacti outside and gradually expose them to sunlight. You should not put them under direct sunlight right away because you’ll burn them.
Instead, introduce one hour of morning sunlight for a day or two. Increase the exposure little by little every week until the cacti are acclimatized to the bright light. Soon after, you will notice that the whitened sections are slowly gaining back the green chlorophyll.
Cactus may turn white because of too much sunlight exposure. It will suffer from sunburn and bleaching with extreme direct sunlight. Stems exposed to intense sun lose their original green color and develop patches of white epidermis that look withered and crispy.
The high UV intensity from the sun destroys the cactus skin that begins to bleach out and turn white. You will know if your cactus is suffering from sunburns if the white patches are like hard superficial calluses. The cactus will also look dehydrated and wrinkled, so watch out for these signs.
White spots caused by intense sunlight are irreversible, and there’s no way to fix them. But it can be prevented by moving the cactus away from direct sunlight to a shaded area. Give the plant a deep watering to compensate for the moisture loss and rehydrate its system.
You should not expose your cacti to intense light to avoid skin burns and bleaching. When the sun gets too hot, use a shade net for your plants to protect them from sun damage.
Sometimes, a cactus turns white due to natural characteristics. Some species have white freckles on their epidermis or white wools on or between areoles, and it won’t appear until the plant reaches maturity.
Cacti such as Astrophytums have natural white spots on their stem as they mature. They appear as tiny white dots or streaks arranged in irregular patterns or sometimes in alignment. The white dots are the distinct characteristic of this species.
Another species of cacti with white spots are the Mammillaria. They have prominent areoles surrounding the stem, and each grows soft white cottony wool. Some cacti lovers have mistaken these wools for pests infestation.
Another reason why cacti have white spots is due to fungal growth. Cacti growing in areas with high humidity is likely to develop white fungus such as powdery mildew. This fungus thrives in moist places and spreads rapidly.
Powdery mildew begins as chalky, white patches on the cacti stem that spreads through fungal spores and infect the younger portion of the plant. The spores attach to the moist stem of the cacti and start growing and reproducing.
Powdery mildew can be treated using a 2% neem oil solution sprayed directly onto the infection during nighttime (to avoid sunburn). In severe conditions, remove and burn the affected parts to keep fungus from spreading.
Position your plant in a well-ventilated area to prevent white fungus from infecting your cactus. When watering cacti, pour directly to the soil so water will not sit on the stem and breed fungal spores.
Cactus with white spots will not die if dealt with immediately. Pest infestation and fungal infection can be fatal in extreme situations. If left untreated, it can cause several plant damages such as dehydration, wilting, and rotten stems.
It is essential to treat infections earlier to save your cactus from dying. Likewise, lack of light and sunburn needs instant action to prevent the condition from worsening.
- There are several reasons why cacti get white spots, including pests infestation, lack of light, extreme sun exposure, natural characteristic, and fungal growth.
- White spots due to pests and fungus attacks can be solved using DIY solutions to eliminate and control their spread. Furthermore, whitened cacti due to sunlight problems are fixed by adjusting their light exposure.
- White spots are not fatal to cacti plants if remedies are applied sooner. Act immediately once the cacti manifest the early signs of damage.
- “Beyond the darkness: recent lessons from etiolation and de-etiolation studies,” by Tegan Armarego-Marriott, Omar Sandoval-Ibañez, Łucja Kowalewska, Oxford University Press
- “Astrophytum asterias,” University Of Arizona
- “Powdery Mildew Factsheet,” Clemson University
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