How to Identify, Treat, and Prevent Powdery Mildew on Succulent Plants
Do you think your succulents may be dealing with powdery mildew? This damaging fungal disease can be difficult to deal with if it starts to spread. In this article, gardening expert and houseplant enthusiast Madison Moulton walks through how to identify, treat, and prevent this fungal disease.
If you’re looking for a group of low-maintenance, almost problem-free plants, succulents are your answer. With a wide variety of species, there is something for everyone, with most preferring neglect over fuss to thrive.
Aligning with their problem-free nature, common garden issues like powdery mildew are not often found on succulents. They prefer to attack tasty vegetables or gorgeous ornamentals instead. However, in the right conditions, powdery mildew on succulents is certainly possible and can greatly impact growth if not tackled quickly.
Luckily, there are a few treatments and plenty of preventative measures that will rid your succulents of this pesky problem in no time.
What is Powdery Mildew?
Powdery mildew is a common garden problem around the world. Caused by various species of fungi, it typically affects vegetable gardeners. But it also affects a wide range of plants, including your precious succulent collection.
To get technical, the species of fungi that causes this disease are part of the Ascomycota phylum. This group contains more than 60 000 species, including the world-famous truffle and even baker’s yeast.
Ascomycete fungi are vital organisms in many industries. They form part of antibiotic treatments and are essential in fermentation, giving us several beloved foods and beverages.
Unfortunately, with this good comes plenty of bad. Some of these species are also pathogens of both humans and plants. They are the reason for annoying apple scab, black knot, and the topic of discussion today – powdery mildew.
What Plants Does This Disease Affect?
Due to their impact on harvesting, most worry about powdery mildew in vegetable gardens. Cucurbits – including cucumbers, melons and squashes – are often impacted due to the many species of fungi that can cause the disease on these plants. Legumes and members of the nightshade family like tomatoes are also quite susceptible.
But veggies are not the only plants to look out for. Many ornamental plants and even trees can fall victim to problems with this disease. One of the garden’s most beloved ornamental plants, the rose, is known for struggling with this fungal disease.
Although it’s not as common as in these plants, it can also latch itself to the succulents in your garden. Brought in by wind, infected soil or spores on nearby plants, it settles on the leaves, leading to a range of unsightly issues. If not controlled, it can greatly impact growth and in severe cases, may end up killing your succulent.
What Are The Causes?
Like many fungi, it grows and spreads the quickest in moderate to warm weather. It cannot handle very high heat or extreme cold, generally growing best in temperatures around 75F.
Spores form in high humidity and spread when humidity drops. Differing from other fungi, powdery mildew does not require water to grow and spread, preferring to attach itself to dry foliage. This interesting growth pattern explains why this disease can be a problem year-round, depending on the specific climate where you live.
For example, the subtropical climate in my garden is the perfect host in spring and summer – prime tomato growing time. Year after year I have struggled to manage this pesky problem on my tomatoes, leading me to attempt growing them in a greenhouse during winter instead.
Moderate temperatures and high humidity are not common around succulents. This explains why this group of plants is not typically affected by powdery mildew. However, if there is little airflow and high humidity around your succulents with just the right temperatures, you may also find yourself spotting signs of this disease on your plants.
Signs Your Succulents Have Powdery Mildew
Powdery mildew is easy to spot on most plants. Covering green foliage, it appears as a dusty white powder that spreads over the surface of the leaves. They extract nutrients from these leaves to develop and spread, impacting growth in the host plant.
In succulents, the signs are a little different. You may notice a white powder on affected leaves, but it is typically not as prominent as it would be on other plants. Instead, you’ll find scab-like lesions on leaves in a brown or rust color, depending on the type of succulent. These lesions may be surrounded by gray or white, but may not.
This can make identification tricky. The lesions look similar to symptoms of sunscald or other common diseases. If you suspect a problem, closely examine the leaves for signs of spores. Also assess the environment around your succulents to determine whether powdery mildew is likely or whether it may be another issue.
Several succulents can experience this disease. However, this disease is most commonly found on Kalanchoe species. Echeveria are also quite susceptible, showing signs on the very tips of the plump leaves.
What To Do When it Appears
Once identified, the first step to take is to isolate the plant. In the right conditions, powdery mildew spreads incredibly quickly, making the problem much harder to control.
For succulents in containers, move them away from any nearby plants to prevent spread. Avoid moving them to an environment drastically different from the one they are currently in as this can lead to further stress.
If your succulents are planted in the garden and the problem is not too severe, you can treat them in the ground. However, if the problem has spread across the entire plant, it is typically better to lift it completely and isolate it. Here, you can see if treatment will be able to save the plant without worrying about any other plants in your garden.
Most advise removing affected foliage once powdery mildew is discovered. However, this can be tricky for succulents. Removing too many leaves can lead to shock, making it difficult for the plant to grow back. The slow-growing nature of these species also means recovery from any damage will be slower and removal of foliage will only slow that process further.
If only one or two leaves show signs of struggle, these can be removed. However, in severe cases, keep the leaves on the plant and treat them with the options below. If powdery mildew persists, you can then remove them or discard the entire plant.
Four Different Treatment Methods
For mild cases impacting only a few leaves on a single plant, you may not need to treat them at all. The problem may disappear on its own if the conditions promoting the spread change. However, if the environment is perfect for the spread of this fungus, it’s best to treat it rather than hope for the best.
To remove existing powdery mildew and prevent it from spreading or coming back, you’ll need to treat impacted plants as soon as possible. The quicker you fix the problem, the easier it will be to eradicate.
For minor issues, there are a number of natural sprays you can use to control the problem. These can be purchased from nurseries, or you can make your own at home.
Many gardeners recommend using sprays containing baking soda. Some recipes use plain baking soda and water, designed to impact spores on contact. Others include soapy solutions to stick to the leaves. Unfortunately, there is little scientific research backing this suggestion, and anecdotal evidence suggests it may prevent problems but not control them.
Organic growers often employ another interesting liquid – milk. This does have some scientific backing in vegetable gardens and may also prove effective for your succulents. Mild infections can be treated with a 1:10 ratio of milk to water, increased if the problem is more severe.
These sprays are usually recommended as preventative measures rather than complete treatments but can help with minor infections.
Commonly used in indoor gardens, neem oil is another preventative measure that can be an effective treatment for minor infections. Diluted foliar sprays spot the spread of the spores, limiting any further damage to your succulents.
When diluting your neem oil, always follow the instructions on the packaging. Recommendations will differ based on your chosen product and its concentration. It’s best to make your own mix rather than purchasing one so you can be sure it is safe for your succulents.
To test for adverse reactions, apply a small amount of the product to one part of the affected plant. If there are no issues, apply to the rest of the plant. You can also apply this mixture to surrounding plants to manage any spread ahead of time.
When applying neem oil to succulents, it’s best to move them to a shady spot for treatment. In full sun, neem oil can cause the leaves of plants to scorch. Once the plants have been treated, you can move them back to their sunny homes.
Copper-based fungicides are commonly used in succulent gardens for a wide range of problems, including powdery mildew. This is the best treatment option for severe infections that have not responded to any of the milder treatments.
Like most of the things on this list, copper fungicide is best used as a preventative spray. However, it is also believed to be effective at controlling existing infections. Choose a low-concentration fungicide and apply according to the package instructions.
Sulfur fungicides are also useful in the control and prevention of powdery mildew when used early on. It’s typically better to apply sulfur as a spray to cover every inch of the leaves, but you can also dust the powder on the leaves.
Follow-up treatments will be required to eradicate the problem completely. Following the product recommendations, applying every couple of days until the plant begins to recover. Keep the powder handy in case any other plants show signs of infection.
It’s better to work toward prevention rather than trying to deal with it later on. These problems are rare on succulents, but still important to consider if conditions around your plants are rife for fungal spread.
Apply these essential tips to not only prevent powdery mildew but also improve the health of your plants.
Space Succulents Correctly
For the best look visually, succulents are often packed into pots or in the ground to fill space. However, if you overdo it, you risk problems with powdery mildew and several other diseases. Giving your succulents enough space will allow air to flow between the leaves and limit the chances of spreading if problems do occur.
Provide Airflow or Ventilation
While space between plants is important, general airflow and ventilation in their local environment are just as important.
This is a concern for succulents grown in contained greenhouses or indoors where little air circulates around the leaves. Avoid placing your succulents in stuffy areas where fungal growth is rife.
Keep Succulents In Full Sun
Powdery mildew thrives in darker conditions. This is also why it often pops up overnight when humidity increases. Succulents placed in low-light areas are far more susceptible than those in ideal full-sun conditions. Full sun will aid in disease prevention and will improve growth at the same time.
Use Preventative Sprays
If you’ve dealt with a powdery mildew problem in your garden in the past, preventative sprays should become part of your regular care routine.
Treatments are far more effective at prevention than control, avoiding problems altogether rather than removing them when they appear. Use natural sprays to avoid damaging the health of your succulents and the surrounding environment.
Powdery mildew may not be common on succulents when compared to other garden plants, but it is not an issue you can forget about completely. Quick action once the problem is discovered will return your succulents to good health in no time.