Black spots on succulents are caused by over watering, sunburn, viruses, frost, trauma and pest infestation.
Here’s a brief look at how each of these potential causes can harm your plants:
Look carefully at the black spots on your succulents. If you notice that the spots are soft and mushy, it is a sign that you have been overwatering your succulent.
In the wild, succulents can survive long periods without water because of their ability to store water in their various parts.
When you overwater your succulents, their tissues become overfilled with water. In turn, this results in bloating, and eventually, the explosion of different plant parts.
In this state, succulents become vulnerable to fungal infections. In fact, the black spots that you see on your plants come from the fungus that is attacking the damages parts of the succulent.
Is it still possible to save an overwatered plant infected by fungus? That depends.
First, remove the affected plant from its pot and inspect its roots. If the roots are still healthy, you can repot it in a new container after removing damaged leaves and stems.
However, if the plant’s roots are mushy, your succulent is probably beyond redemption. It is still possible to use the infected plant’s healthy parts to grow a new succulent. All you have to do is to put these healthy parts in new soil.
Whether you can still save the affected succulent, be sure to throw away the soil where it was originally planted. Do not use it again as it is already infected.
Another common cause of black spots on succulents is sunburn. Although succulents love plenty of sunlight, their parts can become sunburned when it is not given enough time to acclimate to its new location. This usually happens when you buy a new plant from a nursery or when you relocate an indoor plant outdoors.
One sign that your succulent is sunburned is that its black spots are dry.
A sunburned succulent can recover. All you have to do is to remove the damaged part. The more crucial action that you need to undertake is to acclimate your plant to its new location.
If you are moving an indoor succulent outdoors, start by putting it under the morning sun for three to four hours. After that, bring the plant either indoors or in a partially shaded area.
Increase your plant’s exposure to the morning sun by one to two hours every day. At around the fourth day, your succulent is ready for its new life outdoors.
3. Viral disease
Succulents can become infected with viruses in two ways: through insect infestation and the use of infected grafting knives. Plants that succumb to virus infections exhibit symptoms like black spots, stunted growth, and unusual overgrowth of shoots.
Unfortunately, once a succulent becomes infected with a virus, there is nothing that you can do except to discard it. This is why it is critical to disinfect your grafting knives and keep pests at bay.
Most varieties of succulents do not tolerate frost and cold weather. Frost, in particular, can damage plants, one sign of which are dark spots. Prolonged exposure to frost can eventually lead to the collapse of the affected plant.
If you live in a place with cold winters, it is best to keep your succulents indoors. If that is not possible, at the very least, you should use frost cloth to cover your plants.
Succulent varieties with a thick coating of farina or epicuticular wax are susceptible to scratches and puncture marks. Farina refers to the whitish or blueish wax coating found on the leaves succulents. This wax helps the plant repel water.
Scratches and puncture marks often come as a result of poor handling of the plant, especially during repotting. And when a succulent is scratched or punctured, dark spots can form on the leaves.
Unfortunately, you cannot do much to remove these spots. All you can do is wait until the plant grows out of the damaged area.
6. Pest infestation
Succulents are vulnerable to attacks from animals of differing sizes, from small mammals to insects.
It is fairly easy to see when a mammal like a mouse or a deer has attacked your succulent: you will see large chunks torn off.
But when insects and other small organisms infest a succulent, the initial damage may be hard to see at first. Succulents, for the most part, are immune to attack from common garden pests. But left unchecked, an infestation could lead to the death of a succulent.
Here’s a brief look at the insects that typically attack succulents as well as possible remedies.
Mealybugs are small insects, usually growing two to three millimeters long. They derive their name from their ability to produce a white waxy substance. They also secrete a substance known as honeydew which leaves succulents vulnerable to fungal and bacterial infections.
Mealybugs can be usually found in the underside of leaves, roots, and a plant’s joints. Once you notice these insects, act fast as these can easily hop from an infected plant to another.
There are a few ways to remove mealybugs from infected plants.
Some succulent growers soak a ball of cotton in alcohol and apply this directly to the insects. Others prefer to dilute alcohol with water before spraying on the affected plant. If you don’t want to use alcohol, you can use dish soap diluted in water.
If the mealybugs have infested the roots, remove the plant from its pot. Remove the soil and rinse the roots until the bugs are completely removed. You can spray the roots with either alcohol or diluted dish soap.
Allow the plant to dry completely before transferring it to a new pot.
Be warned: it may take many tries before you get rid of mealy bugs completely. While the plant is still infested, separate it from your other plants.
Out of the thousands of species of scale, the armored scale and the soft scale are the two most common insects that attack succulents. These two feed on the sap, damaging the plant and leaving it vulnerable to diseases.
A scale infestation often manifests itself in the form of black or brown spots.
If the infestation has just begun, you can manually remove these insects or scrape these off. However, if the infestation has become severe, you can use the same treatment used in a mealybug infestation: wipe alcohol-soaked cotton directly on the insects or spray diluted alcohol. Alternatively, you can use neem oil instead of diluted alcohol.
You should also check the roots for any presence of these bugs. If you find scale on the roots, wash off the plant, including the roots. Afterward, spray the plant with diluted alcohol and allow it to dry before repotting with fresh soil.
It will often take a week until you can totally get rid of scale. During this period, you need to quarantine the infected plant.
Also known as plant lice or greenflies, aphids feed on the leaves and flowers of plants.
These insects also secrete honeydew which not only leads to the development of molds but also attracts ants.
There are a few ways that you can treat a succulent infested with aphids.
The easiest way to do that is to use water pressure to remove the insects.
You can also spray diluted soap on the affected parts. Some people add vegetable oil to this mixture.
Spider mites are arachnids, not insects. They are related to spiders and scorpions. These small creatures feed on the sap of plants.
Succulents infested by spider mites will first change to a lighter color before turning white.
Apart from the change in color, you will also notice brown spots on your plant as well as webbing produced by the spider mites.
Treatment for a spider mite infestation is similar to mealy bug and aphid infestations.
Whiteflies often target the leafier succulent species. These insects can be typically found hiding beneath leaves.
When you notice whiteflies on your succulents, act fast as these insects are notorious for reproducing quickly.
These insects can be blasted off with water. Alternatively, you can spray either soapy water or diluted alcohol directly on the affected plant.
Fungus gnats are attracted to moisture. That is why overwatered succulents are vulnerable to these insects.
Although less harmful than other pests, fungus gnats can be hard to get rid of.
To get rid of these pests, remove the very thing that attracts them: excess moisture. Change your watering habits and consider changing the soil you use for your succulents if it is not fast-draining.
You can also sprinkle cinnamon powder on your potting mix or place a flytrap near your plants.
Unlike the previously mentioned insects, ants do not directly damage succulents.
Instead, these insects do indirect damage to your plants because they farm other insects like aphids and mealybugs which produce honeydew.
You can get rid of ants by placing sugar water near your affected succulent.
The more important task that you need to do is to get rid of the insects the ants have been farming on you succulent.
A sign of a bigger problem
When you notice black or brown spots on your succulent, quick action is required. Usually, these spots indicate that a larger problem is at hand. Your prompt action can help stave off a more severe problem quietly lurking in the background.
Image: istockphoto.com / AlxeyPnferov