Solving the Powdery Mildew Puzzle: How to Protect Your Houseplants

Powdery mildew is among the most common problems for houseplant owners. This sneaky fungus can quickly spread and take over your plants if left untreated, leaving you with a garden full of unsightly, sickly-looking plants. But fear not; with the right knowledge and tools, you can successfully combat powdery mildew and keep our houseplants thriving.

What is Powdery Mildew?

In simple terms, it is a type of fungus that infects plants, creating a white, powdery growth on leaves and stems. The most common type of powdery mildew is caused by the fungus Erysiphe cichoracearum. This fungus thrives in high humidity conditions and poor air circulation, making it a particularly problematic issue for those growing cacti and succulents indoors or in greenhouses. Powdery mildew fungi are considered among the most common plant diseases for indoor houseplants.

List of Susceptible Plants

Although this Mildew can infect many types of healthy plants, some plant species are more susceptible than others.

Cucumber
Pumpkins
Lilac
Melons
Peas
Peonies
Lime

Symptoms of Powdery Mildew

In severe cases, the fungus can also cause distortion of leaves, yellowing, wilting, and even death of the plant.

1. White, powdery spots on parts of the plant: These spots may start small, but they can quickly spread and cover a large portion of the plant if left untreated. These patches can appear on the leaves, stems, and even the flowers of the affected plant. They are often circular or irregular in shape and can quickly spread, covering large areas of the plant.
2. Leaf edges curl upward: Another symptom is the curling of the leaf edges. This is a result of the fungal growth causing the leaves to dry out and become brittle. As the leaf edges curl upward, they may also take on a yellow or brown color.
3. Premature fruits: Powdery mildew can affect the fruit of plants, causing them to develop prematurely and fall off the plant before they are fully ripe. These fruits will be smaller, discolored, and less sweet than normal.

It’s important to note that powdery mildew is not only unsightly, but it can also have a negative impact on the overall health and vitality of your cacti and succulents. The fungus can interfere with photosynthesis, weakening the plant and making it more susceptible to other diseases and pests. Therefore, it’s essential to keep an eye out for the symptoms and address the issue as soon as possible.

Causes of Powdery Mildew

• High humidity: Powdery mildew thrives in high humidity conditions and poor air circulation. This makes it a particularly common problem for gardeners growing cacti and succulents indoors or in greenhouses, where the environment can be more controlled, and the humidity may be higher.
• Presence of the fungus in soil or plant debris: The fungus that causes powdery mildew can survive in soil and on plant debris, making it easy to spread to other plants, even if the growing conditions aren’t ideal for the fungus.
• Susceptible plant species: Some cacti and succulents are more susceptible than others, so it’s important to be aware of the specific needs and vulnerabilities of the plants you’re growing. For instance, species of the genus Echinopsis and Opuntia are more resistant to powdery mildew than other cacti species.

Treatment of Powdery Mildew

1. Remove affected plant parts: One of the first steps in treating powdery mildew is to remove any visibly affected leaves and stems. This helps prevent the fungus from spreading to other parts of the plant and can also improve the overall appearance of the plant.
2. Natural Treatments: Neem oil, horticultural oils, soda, squash, and compost have all shown positive results when applied to the leaf surface.
3. Improve air circulation: Powdery mildew thrives in conditions of poor air circulation, so one of the best ways to combat it is to improve the airflow around your cacti and succulents. This can be done by increasing the distance between plants or using a fan to circulate the air.
4. Use a fungicide: Several fungicides are available to treat powdery mildew. Be sure to choose a fungicide safe for use on cacti and succulents. These fungicides can be applied as a foliar spray or a soil drench. Potassium bicarbonate and sulfur are good contenders.
5. Keep the humidity low: Keep the humidity around your cacti and succulents low, as the fungus thrives in high humidity conditions. 
6. Keep an eye out for re-occurrences: Keep monitoring your plants for any signs of the fungus re-occurring, and address it immediately.

Prevention of Powdery Mildew

Preventing powdery mildew on cacti and succulents is easier than treating it once it has taken hold. 

• Choose resistant plant species: As mentioned earlier, some cacti and succulent species are more resistant to powdery mildew than others. Consider choosing plant species that are known to be less susceptible when planning your garden.
• Maintain good growing conditions: Keep your cacti and succulents in an area with good air circulation, and avoid overcrowding. This will help to prevent humid conditions.
• Keep your garden clean: Regularly remove dead leaves, flowers, or debris from your cacti and succulents. This will prevent the fungus from spreading.
• Use a preventive fungicide: Some fungicides can be used as a preventive measure to stop powdery mildew from taking hold. Be sure to choose a fungicide safe for use on cacti and succulents, and follow the instructions carefully.
• Regularly inspect your plants: Keep an eye out for symptoms of powdery mildew, and address any issues as soon as they are noticed.

Powdery mildew is a common problem for gardeners growing cacti and succulents, but it can be avoided with the right knowledge and preventative measures. By understanding the symptoms, causes, and treatment options, you can watch out for powdery mildew in your garden and address it quickly if it does appear.

As always, happy gardening!