How to Get Rid of Powdery Mildew on Plants

One of the most widespread plant diseases is powdery mildew. This common fungus thrives best in climates that are warm and dry. Powdery mildew appears as a white fuzzy fungus on plants. It’s easily recognized by the spots and patches of white and gray mold that appear on plant leaves and stems. When allowed to grow uncontrolled, powdery mildew will quickly take over a plant and ultimately cause its demise.

While many plants are vulnerable to powdery mildew, many others are resistant to infection. If the disease is a problem in your garden, you can help mitigate the problem by choosing disease-resistant plants to grow.

There are also many treatments you can purchase to help plants that have become infected. Platt Hill Nursery sells a range of powdery mildew solutions for gardeners. If you’re wondering how to get rid of powdery mildew, the professionals at Platt Hill Nursery can help.

What is Powdery Mildew?

Powdery mildew is a fungus that affects almost all types of plants, from vegetables to flowers, fruit trees to forest trees. Powdery mildew gets its name from its appearance: white and gray colored, and powdery in texture. It appears on the surface of the leaves and can be found on other plant parts as well. After powdery mildew has infected a part of the plant, the leaves may turn yellow, and then brown. Powdery mildew can also cause leaves to become shriveled, dry, and distorted.

Powdery mildew is not just one type of fungus. Different types of powdery mildew affect different types of plants. For example, a powdery mildew found on a rose is not the same as a powdery mildew found on a squash. Powdery mildew needs a living plant to grow on, so when the plant dies, so does the mildew.

Powdery mildew produces spores that spread through the air. Water can prevent powdery mildew from spreading, so powdery mildew is most common in semiarid regions and less common in areas where high amounts of rainfall occur. Powdery mildew prefers warm days and cool nights. When leaf temperatures rise above 90°F, powdery mildew can die. Greenhouse conditions are often good for powdery mildew fungi, so sometimes growing plants in these conditions can be difficult. It’s important to use best practices for controlling powdery mildew in this type of environment.

Powdery Mildew Life Cycle

Powdery mildew is a white mold that grows on living plants. On plants that survive from one season to the next, powdery mildew survives from one season to the next. On trees, it can survive on the bark of branches as well as on stems.

Powdery mildew grows on the surface of affected plant parts in thin layers called mycelium. Spores of powdery mildew are produced on the upper leaf surface, on fruits, flowers, and on herbaceous stems.

The wind carries the spores of powdery mildew to new hosts. When leaves are dry, this is when powdery mildew spreads best. If the leaves become wet and stay wet, this kills the spores of powdery mildew and prevents them from spreading.

Which Plants Are Most Susceptible to Powdery Mildew?

There are many species of plants, trees, shrubs, field crops, and garden plants that are susceptible to powdery mildew. The following are examples of plants that may become infected with powdery mildew:

Powdery mildew treatment can help save plants, but powdery mildew is difficult to eradicate. It’s much easier to prevent powdery mildew than it is to get rid of it.

Identifying White Mold on Plants: Key Signs and Symptoms

Although there are many different types of powdery mildew, the symptoms of powdery mildew tend to be the same on most plants. Here’s what to watch for in your garden:

• White or gray spots on leaves, similar to talcum powder, found on the upper sides of the leaves
• Distortions in the leaves, with leaves becoming curled or shriveled
• Leaves may turn yellow and then fall off
• Tiny spherical fruiting structures that turn black as they age, may be clustered or in singles

The spherical fruiting structures described above are the cleistothecia, the overwintering bodies of fungus. These fruiting bodies crack open in the spring and release the spores that infect other plants.

If you’re having a hard time identifying powdery mildew on your plants, you can always send in a picture or bring a photo of your plants to Platt Hill Nursery, where our experts can easily identify problems like powdery mildew and downy mildew, two very common types of plant fungus.

Common Causes of Powdery Mildew

The severity of the powdery mildew depends on many environmental factors including the weather conditions during the growing season, age and condition of the plant, and the type of host plant. High relative humidity is best for spore germination, so the disease spreads quickly in locations where plantings are crowded and air circulation is poor.

As the relative humidity rises to 90 percent, the spread of the powdery mildew only grows. If the leaf surfaces become actually wet (like through a rain shower or because of a sprinkler), then spores cannot spread. Older growth is less susceptible to powdery mildew than young growth.

Once you know the conditions under which powdery mildew can grow, then you can prevent it from growing. Keep this in mind as you’re planting your garden.

Natural Powdery Mildew Treatment

There are many methods for treating powdery mildew. Here are some tips to follow:

• Avoid late-summer nitrogen fertilizer applications to slow the production of vulnerable succulent tissue.
• Remove all infected plant parts. If infected plants have reached the end of their life cycle, remove all parts of the plant and destroy them. This can prevent the powdery mildew from surviving in the soil during the winter.
• Avoid doing anything to increase the relative humidity of a location. For example, avoid overhead watering, or crowding multiple plants together.
• Never put infected plant parts in a composter.
• Prune plants to increase air circulation and reduce humidity in the vicinity around the plant.
• Consider rotating crops to slow the spread of powdery mildew. Remember, different types of powdery mildew affect different types of crops. Avoid planting crops of the same plant families in the same location year after year.

In addition to the suggestions above, there are many treatments that you can buy from nurseries to help stop the spread of powdery mildew throughout your garden.

Neem Oil

Neem oil is a botanical pesticide that comes from the neem tree. Neem oil is effective against fungal diseases including powdery mildew. It works best to eradicate diseases, but can also be used (to less effect) to protect plants.

To use neem oil to eradicate a disease, apply it on a 7-day schedule according to the instructions. To prevent disease, apply neem oil on a 14-day schedule, according to the instructions. Keep in mind that neem oil can burn leaves or flowers, so it’s important to always read the instructions and avoid applying neem oil within two weeks of using a sulfur spray.

Neem oil powdery mildew treatment is something that experts at Platt Hill Nursery commonly recommend to gardeners to help get rid of their powdery mildew. To find neem oil, visit our store. Have questions about neem oil? We have answers! See our previous guide to everything you need to know about neem oil.

Copper

Copper is a well-known, effective treatment for powdery mildew. Copper was used for centuries in European vineyards to treat powdery mildew, and it’s still in use today in gardens around the country. Copper fungicides are best when applied at the very beginning of an infection, either before symptoms are visible or just as symptoms have begun to show.

As with other fungicides, read the instructions carefully to ensure that you’re using copper fungicide correctly. Never apply copper fungicide on hot days or with other chemicals.

The Role of Humidity and Air Circulation in Controlling Mildew

Powdery mildew spreads best in high relative humidity. Controlling air circulation can help prevent the spread of powdery mildew, by keeping air around the plants fresh and dry. Some tips for controlling air circulation around plants:

• Avoid overcrowding plants. Follow expert recommendations for spacing plants.
• Stake plants to help them grow above the ground. Train plants to grow up high on stakes or fencing.
• Prune selectively. Eliminate unnecessary leafy growth to promote good air circulation around the plant.
• Use drip or soaker irrigation. Avoid overhead watering to prevent air around plants from becoming humid. If you must water overhead, water in the early morning so the plant can dry as the sun rises.

Pruning and Plant Care Tips to Reduce Mildew Risk

Pruning away disease can help control the spread of powdery mildew, provided that you’re careful about how you prune and the tools you use.

• Clean tools with a 10% bleach solution to prevent the spread of powdery mildew. Dip your tools in the solution and dry them before putting them away.
• Prune only the most infected parts of the plant during the growing season. Pruning your plants will prompt them to produce succulent growth, which is more susceptible to powdery mildew. Burn or dispose of the powdery mildew-covered debris in a sealed plastic bag. Avoid excessive pruning.
• Prune during winter months to promote good air circulation. Pruning at colder times of year will not prompt as much growth, and gives you an opportunity to create less than ideal conditions for powdery mildew.

Seasonal Maintenance: Preparing Your Garden for Mildew-Free Growth

You can prevent powdery mildew throughout the growing season.

Spring

• Install a drip irrigation system
• Give plants adequate space in the garden during planting
• Prune early to improve air circulation
• Train plants to grow up

Summer

• Watch for signs of powdery mildew, treat as needed

Fall

• Remove debris from infected plants quickly, burn or throw away in a sealed container

Winter

• Prune selectively to improve air circulation
• Clean empty ceramic pots for spring planting, get rid of any leftover plant debris inside

Want more tips about how to get rid of powdery mildew? The experts at Platt Hill Nursery have treatment recommendations of all kinds. We can help! We have advice to share from tips for growing bee balm to information about how to take care of roses. We can help you with outdoor and indoor plant pests, and plant insects. Stop by our Carpentersville or Bloomindale location with your questions, or contact us today.