Succulents are stunning garden and houseplants that add semi-desert vibes to indoor and outdoor spaces. These plants are easy to care for and can survive various growing conditions, even tolerating a little neglect. However, these plants are super sensitive to overwatering, which brings many bacterial and fungal infections. In this article, let’s talk about how to get rid of mold on succulents.
Healthy and succulent container garden free from insects, pests, and fungal diseases Photo Credit
These fungal diseases deteriorate the health of your plants, covering the entire plant. Fungal infections lead to defoliation if left untreated, thus encouraging the invasion of common houseplant pests. They taint the beauty of rosettes and cause stunted growth. Mold occurs due to poor aeration and improper watering. Mold on succulents is easy to treat with organic and inorganic treatments (synthetic fungicides).
Powdery mildew, sooty mold, grey mold, anthracnose, and leaf spots are common ones on most indoor and outdoor succulents. Let’s learn more about these diseases, their causal factors, and how to get rid of them successfully.
What is Powdery Mildew?
A severe powdery mildew infection on cucumber leaves Photo Credit
Powdery mildew disease widely occurs on succulents because this fungus thrives in similar conditions as these plants.
On infected plant surfaces, this disease appears as white patches of powdery mildew spores like talcum powder.
As this disease progresses, these patches turn into yellow or brown spots, ultimately black. These spore masses (powdery coating) also cover the stem and leave, causing the distorted appearance of plants.
Note: The causal agent of this disease is Podosphaera xanthii, and this fungal agent has a broad host range, including fruit trees, grasses, vegetables, and ornamental plants (roses, spring perennials, and succulents). In spring perennials, powdery mildew fungus negatively impacts the leaf and flower buds (preventing the opening of buds).
This powdery mildew on succulents occurs when weather and growing conditions are warm and dry. Podosphaera xanthii pathogen requires higher humidity levels instead of wet leaf surfaces for spore germination.
Therefore, the disease occurrence is more in dense plantations compared to well-spaced perennials. It is because these plantations have poor air circulation in highly humid environments.
Note: Powdery mildew on succulents occurs in humid environments with dry soil conditions. This fungal pathogen infects the young succulents more poorly than the older and established ones. It remains on the leaf surfaces, penetrates the plant tissues through infection peg, and interrupts food-making. These fungal spore masses spread to other plants during the wind or watering and can destroy the entire succulent garden.
Related: 25 Beautiful And Easy To Grow Purple Succulents For Homes & Offices
What is Sooty Mold?
Sooty mold is a black-colored fungus that grows on plant or leaf surfaces covered with honeydew (sticky substances). These sticky materials are secreted by piercing-sucking insect pests, such as aphids, whiteflies, mealybugs, and scale insects, and attract the fungal species of Capnodium, Fumago, and Scorias genera. These fungal species accumulate over honeydew deposits and flourish.
Black mold fungal species are decomposers and feed on the decomposed honeydew molecules as nutrition. They do not cause any harm to host plants residing in them but block the sunlight absorption process, ultimately reducing the efficiency of photosynthesis and plant health.
The name ‘sooty mold’ comes from the dark thread-like growth of the fungal bodies or mycelium resembling a soot layer.
A severe black sooty mold infestation on the host plant, while the white powdery creatures are aphids. Photo Credit
Honeydew is a sweet, sticky material from the digestive system of sap-sucking insects when they feed on plants. These sap feeders cannot digest the nutrients completely absorbed from plant tissues and excrete them as waste wherever this sticky material attracts the growth of black mold fungus or decomposers.
Scale insect infestation on Aloe plant with heavy excretion of honeydew Photo Credit
What is Gray Mold?
Grey mold is a fungal disease and infects succulents during their active growing season. The causal agent of this disease is Botrytis cinerea. Damp and cool weather conditions favor the disease development, and windy weather spreads the grayish spore masses over large distances and other plants.
The infected succulent plants appear gray due to the covering spore bodies. Their foliage turns yellow and starts rotting as the infection progresses.
Botrytis cinerea mycelial growth on new buds of the rose plant Photo Credit
Related: 25 Beautiful Flowering Succulents To Grow Indoors (With Pictures)
How to Get Rid of Mold on Succulents—Organic and Inorganic Methods
Many chemical treatments are available to control mold spores on succulents. However, these only bring the best results when used with cultural practices and preventive measures.
The following are the best ways to prevent powdery mildew, sooty mold, grey mold, leaf spots, and other fungal diseases.
- To prevent powdery mildew on succulents, prune off the infested foliage of succulents. Also, remove the older leaves because they are more prone to infection.
- Avoid overhead irrigation of potted plants to reduce the relatively high humidity; otherwise, the highly humid environment favors the powdery mildew spore germination.
- Do not apply nitrogen fertilizers in late summer because it promotes vegetative growth, which is susceptible to pest infestations.
- Allow the potting soil of succulents to dry out completely to discourage root rots from soggy soil.
- Remove the infected plant and do not use them for compost because the temperatures are not hot enough to kill the powdery mildew spores.
- Space out the succulents properly because overly crowded places do not have room to dry rain or irrigation water completely.
- Use drip irrigation or a garden hose to water your plant without wetting the leaves of succulents. Otherwise, the wet leaves are at higher risk for grey mold and powdery mildew infections.
- Water your succulents in the morning, once a week, so they have enough time to absorb and dry after watering.
- The succulents’ powdery mildew can be managed with chemical treatments, such as the application of neem oil, sulfur, triforine, and potassium bicarbonate.
- Neem oil sprays are effective against many sap-sucking pests (aphids, mealybugs, whiteflies, and scales). It kills them on infected leaves by interrupting their feeding process and dissolving their body coverings. Neem oil solution also disrupts the growth of regulatory hormones. Mix four drops of neem oil with one teaspoon of dish soap per 400ml of water to prepare the neem oil spray. Pour the solution into a spray bottle and apply it on succulent leaves to wash off the fungus growth and kill insects.
- Use Mycostop to kill the infections of Botrytis mold. Mix the 5 gm/ 50 liters of water for foliar spray and apply this solution at 14 days intervals.
- Treat powdery mildew on succulents with horticultural oil applications. Mix one teaspoon of oil with two teaspoons of dawn dish soap per litter of water and apply this solution every other day to kill the fungus bodies.
- Apply green cure fungicides to kill insects upon contact. It is effective for all mold pathogens and prevents succulents from damage.
Related: Best Ways to Propagate New Succulents from Leaves and Cuttings
Copper-based fungicides on treating all kinds of molds safely (without damaging the beneficial insects and plant’s cosmetic value) Photo Credit
What are the Best Fungicides for the Treatment of Mold on Succulents?
The following are the best treatments against mold fungi on succulent plant soil and leaves.
Green Cure
This fungicide is highly effective against powdery mildew infections on plants, mainly indoor succulent gardens. It contains 85% potassium bicarbonate and is best for organic gardening applications.
Benefits of Using GreenCure Fungicide
- Best for organic gardening practices with no harm to beneficial insects.
- It has residual effects of two weeks.
- Ideal for indoor and hydroponic gardens.
Mycostop
It is a biological fungicide developed from the bacterium Streptomyces griseoviridis. It is best in the killing of overwintering spores of gray mold fungus.
Benefits of Using Mycostop Fungicide
- This biological protects from many fungal pathogens, such as Fusarium wilt, Pythium, and Botrytis cinerea.
- It inhibits the growth of root rot pathogens.
- Improves plant vigor and immunity against pathogens.
FAQs on Sooty Mold and Powdery Mildew Fungus
What Kills Mold on Soil?
The mold on succulents indicates an improper care schedule, particularly with overwatering and poor drainage. However, with proper care and maintenance (watering schedule), the mold on indoor succulents can be eliminated. The best way to get rid of mold on houseplant soil is
- Repot the succulent plants into a clean and sterilized pot filled with fresh potting mix.
- Allow the potting soil to dry out completely before the next watering.
- Move the indoor succulent plants outdoors in summer for bright direct sunlight exposure for at least six hours per day. It will dry the potting soil while killing the spores and fungal structures.
- Apply neem oil solution as a soil drench to kill fungal pathogens
- Mix perlite as equal parts with potting soil to improve drainage because these beautiful plants do not like wet feet.
Will Rubbing Alcohol Hurt my Cactus?
Yes, rubbing alcohol will hurt your cactus plants immediately after application. The only way to keep the mealybugs and spider mites away from the cacti is to apply systemic insecticides, such as dinotefuran, to kill the damaging pest immediately.
Can I Use White Vinegar to Get Rid of White Mold on Plants?
White vinegar is the most effective method to kill white mold on succulents without harming plants. To eliminate this fungal disease, mix one tablespoon white vinegar with a quart of water and pour it into a spray bottle.
Apply this solution to leaves and soil carefully and repeat this process every three days until the disease disappears.
What is the Best Fungicide for Succulents?
The copper-based fungicides are the most effective ones to kill mold on succulents without damaging their cosmetic value.
Another best fungicide to treat mold on succulents is baking soda. Combine one tablespoon baking soda with three teaspoons of dish soap and one liter of water. Apply this solution to plants with a weekly plan in the morning or evening when the beneficial insects are not around.
Can you Sprinkle Cinnamon Directly on Plants?
Cinnamon is an excellent insect repellent and rooting hormone and has fungicidal properties. However, its overapplications lead to toxicity and kill the plant.
Apply the cinnamon powder onto the soil to kill gnats larvae and eggs of other soil-dwelling pests, but do not directly onto the foliage.
How do you Get Rid of Mold in Succulent Soil?
The mold disease in the potting soil of succulents is due to improper watering and poor drainage. To treat the mold in succulent soil, sterile the ground before using it in potting.
Add two teaspoons of cinnamon powder and thoroughly mix it with the earth. This application will prevent future mold infestations in the soil.
When watering your succulent, ensure the excess water has drained out of the pot entirely. Moreover, water your potted succulent more frequently in growing seasons than in winter. Situate their containers in the brightest indirect sunlight spot to discourage mold fungus growth.
What is the White Cotton Stuff on the Cactus?
This white cottony stuff on your cactus is mealybugs or adult cochineal scale insects. These sap-sucking bugs infest the newer growths of your plant and remain hidden in the rosettes of leaves. Mealybugs feed on new developments and continue to thrive and survive while damaging the plant.
To deter these pests, use isopropyl alcohol-dipped Q-tips and rub the infested areas of your cactus plant. Or you can also remove them manually when in low numbers.
Apply insecticidal soap with half-strength dilutions every week throughout the growing season to kill these sap feeders’ population’s pests.
What are the Tiny Black Spots on my Succulents?
These black spots on your succulent plants are due to several reasons. It can be water warts caused by Pythium fungus or overwatering, root rot, chemical burn, insect pests, and viral infections.
To treat these black spots on your succulents, avoid overwatering and allow the potting soil to dry out completely. Repot into a new pot with fresh potting mix and prune off the rotten roots to prevent further damage. Apply fungicide sprays in early spring to inhibit the spore germination, letting the plant thrive.
What Does Scale Look Like on Succulents?
The infestations of scale insects on succulents are easy to spot. They appear as raised small bumps of dark brown or black.
Scale insects thrive on the tasty nutrients of the succulents, and if left untreated, they’ll continue to multiply and feed. Their constant feeding leads to foliage damage.
When removed from host plants, these scales leave behind sticky substances and powdery masses that reduce the aesthetic value of plants.
How often should Succulents be Watered?
There is only one rule to water your succulents: water only when the soil of your plants is bone dry. Apply once a week (growing season) for your indoor potted plants and every two weeks in winter.
In contrast, outdoor groundcovers require watering thrice per week, particularly in the summer season and once a week in winter.
What are the Signs of Mold Sickness in Plants?
The most common sign of mold diseases in plants is the development of brown spots on leaf and flower buds. Cottony masses (fungus bodies or mycelia) are also present on the infested leaves and flowering stalks. At the same time, the symptoms of infection are defoliation and browning of leaves with stunted growth.
Sources for Further Reading
- Gray mold in the flower garden. (n.d.). UMN Extension. Retrieved October 17, 2022, from https://extension.umn.edu/plant-diseases/gray-mold-flower-garden
- Colorado State University Extension. (2016, February 22). Powdery Mildews – 2.902. Extension. Retrieved October 17, 2022, from https://extension.colostate.edu/topic-areas/yard-garden/powdery-mildews-2-902/
- Sooty Mold Management Guidelines–UC IPM. (n.d.). Retrieved October 17, 2022, from http://ipm.ucanr.edu/PMG/PESTNOTES/pn74108.html
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