Looking after a Christmas Cactus can be highly rewarding, as these plants are durable and tolerant of several environmental conditions. However, Christmas Cacti are also highly susceptible to pathogens and diseases that can eventually cause spots on the leaves. These different-colored spots are symptoms that the plant’s health is at stake.
So, why does a Christmas Cactus have spots on its leaves?
- Brown spots relate to Botrytis Blight.
- White spots are a consequence of impatiens necrotic spot virus (INSV) or mealybugs.
- Black spots derive from the Drechslera cladophyll rot or mealybugs.
- Yellow spots might be a consequence of Basal Stem Rot.
In the worst cases, plants affected might have to be destroyed.
There are some solutions to these pathogens, but you will need to act fast to save the plant. Below, you can find the symptoms and potential solutions to these diseases.
What Are the Spots on Your Christmas Cactus?
First of all, it is essential to notice that, in most cases, the spots on the leaves of your plants directly relate to deadly pathogens such as fungi, bacteria, and viruses. Sometimes, the lesions are the result of an infestation of bugs, such as mealybugs.
The appearance of spots on your Christmas Cactus can derive from environmental factors such as overwatering in the case of Stem Rot. However, other aspects to watch out for include poor air circulation, low temperatures, improper light conditions, and high-humidity.
As mentioned above, as the disease that is affecting your plants starts to spread across the leaves, you might have to consider whether it is worth trying to save your plant. Indeed, failed attempts can increase the chances of nearby plants contracting the pathogen too.
Below, you will find the potential solutions you could employ, yet understanding whether it is worth going ahead with them depends on the current state of your plant.
Brown spots on the leaves of your Christmas cactus are common. They can be the consequence of sunburn or sunscald, especially if they appear where the leaves are at their thinnest, usually along the edges.
However, in most cases, these spots are relatable to Botrytis blight, a fungal disease that affects millions of plants worldwide each year.
Also commonly found in roses and ornamental trees, the color of the spots caused by Botrytis blight can vary from brown to reddish. However, the brown lesions are usually accompanied by the grey mold that is characteristic of this fungus.
Therefore, to ensure that you are dealing with Botrytis blight and start the treatment to get rid of it, you should look for the grey mold taking over the central part of the leaf. Other symptoms of this condition include wilting leaves, spotting, and discoloration of the plant.
When attempting to treat botrytis blight, you should ensure that the disease is still at its first stages. At first, botrytis blight will tend to attack old, already weakened leaves, and then move over to the healthy ones.
Start the treatment by pruning, collecting, and destroying the parts of the plants affected by the fungus with sterile shears. Remember to clean the shears with alcohol after every cut to avoid spreading the disease to healthy branches.
After burning the affected leaves, proceed to make the plant as comfortable as possible, which includes limiting stress and making sure it receives the right amount of sunlight and nutrients. When watering your plant, keep the leaves dry, pouring the water into the soil.
Lastly, if your Christmas cactus lives outdoors next to other plants, you should consider using a fungicide on nearby branches as the spores can travel far.
White spots on your plant can have two different causes: Impatiens necrotic spot virus (INSP) or mealybugs. It is possible to tell the diseases apart by comparing the white spots.
- Mealybugs – these insects can reproduce and multiply quickly. As they feed on the plant’s nutrients, they will expel any sugar in excess, creating honeydew, a white, fuzzy substance.
- Impatiens necrotic spot virus – the INSP is a plant pathogenic virus that causes several symptoms, among which wilting, decay, and sunken spots on the leaves. These spots are not always white, depending on the variety and the virus strain. Usually transmitted by Thrips, this virus is more common in outdoor and greenhouse plants and can quickly transfer across your garden.
As the Impatiens necrotic spot virus spreads, the only way to limit its damage is to use a potent insecticide that allows you to eliminate the transmitting vector before it reaches nearby plants.
However, prevention is crucial. If you are growing your Christmas cactus in your home, everything you will have to do is ensure that any new plant you bring in is healthy. Lastly, if the plant is too damaged for treatment, you might have to destroy it.
Black spots on your Christmas cactus are often a consequence of the Drechslera cladophyll rot, also known as Helminthosporium cladophyll rot. This disease derives from the Drechslera Cactivora fungus, which creates sunken, circular lesions along the surface of the leaves. The black spores of these lesions will look fuzzy or moldy.
Another culprit for black spots on the leaves of your Christmas cactus is mealybugs. Indeed, the honeydew they produce and leave on the surface of the leaves can become a cradle for sooty mold. This fungus is another pathogen that can cause the decay of the leaves of your plant. In this case, lesions won’t necessarily be circular, but they are also fuzzy.
While the sooty-mold itself is not detrimental for your plant itself, it can spread quickly and fast enough to prevent the sunlight from reaching the leaves of your plant. Without the necessary exposure to light, your plant will become weak or die.
In both cases, if the plant is in a greenhouse or garden, you should proceed to isolate it and destroy it immediately. Indeed, the spores of these fungi can travel far and become highly dangerous for your whole crop.
If you have been growing your plant indoors, you should:
- Mealybugs: in the case of isolated plants, you can manage the issue by spraying a pesticide onto the leaves of the plant. However, since mealybugs reproduce quickly, you should also collect and destroy any affected branch, stem, or leaves.
- Drechslera cladophyll rot: this disease is harder to manage, and, in most cases, you will have to destroy your plant. However, if the damage is only limited to a single indoor plant, you could opt to get rid of any affected part and keep water to a minimum. Avoid watering the plant from above: keep the splashing to a minimum to avoid spreading the spores further.
Yellow spots on a Christmas cactus can derive from several conditions, including root rot, sunburn, or stem rot. However, the last one, Basal stem rot, can potentially be deadly for your plant if not treated immediately, so you should check for signs of this disease before treating your plant for secondary issues.
Indeed, root and stem rot appears in the roots or lower stem of your plant as brown, moldy, or mushy lesions. It also makes the leaves appear droopy. As it spreads, it can prevent the plant from absorbing the necessary nutrients from the soil.
If you can still save the plant, remove it from the current container, and get rid of the old soil. Then, gently wash the roots under running water until most of the affected ground is gone. Cut off all the roots attacked by the pathogen or mold and transplant the Christmas cactus into fresh soil.
Independently from their color, spots on the leaves of your Christmas Cactus can indicate that your plant is affected by a fungus, pathogen, bugs infestation, or virus. These diseases are among the most difficult to fight, and you might have to eradicate the plant. However, prevention in these cases is essential to manage and limit the spread of the disease.