Powdery mildew causes unsightly patches of gray or white fuzzy growth on your Crape Myrtle’s leaves and blooms. If left untreated, the disease can spread and cause big problems for your plant, possibly even robbing you of blooms! So, what can you do about this dreaded disease?
Powdery mildew is a common and treatable condition caused by fungal growth on your Crape Myrtle. Planting your Crape in full sun and removing suckers is key for prevention, but sometimes treatment is necessary. Synthetic fungicides and natural remedies can be effective in combating powdery mildew.
After we explain exactly what powdery mildew is and what it does, we’ll share all our secrets for how to eradicate the fungus from your Crape Myrtle. Whether you want a chemical treatment or an all-natural remedy, there are quite a few options for dealing with this disease.
What is Powdery Mildew?
Powdery mildew is a very common plant disease that affects virtually all kinds of plants, trees, and shrubs. Crape Myrtles are no exception, as powdery mildew is one of the most common problems these trees and shrubs face. The disease is caused by the presence of the fungus Erysiphe lagerstroemiae.
The fungus grows on the surfaces of the tree’s leaves, shoots, buds, and flowers. It has a powder-like appearance, giving it the name “powdery” mildew. Powdery mildew can usually be identified by its appearance alone. The result is patches or thin layers of white or grayish powdery growth.
Young plants are most susceptible to this fungus, as powdery mildew grows best on young Crape Myrtles. In some cases, the powdery mildew can cover all the plant’s new growth, causing severe damage to those areas. New growth affected by powdery mildew can be distorted, dwarfed, or completely covered with the fungus. Leaves that become infected typically die and drop off the Crape Myrtle sooner than the other healthy leaves.
Older or mature plants are less likely to be infected, but they’re not immune. Even mature plants can have their blooms stunted by powdery mildew. Fully coated buds or heavily infected flowers may not open, and other diseased areas can suffer stunted growth.
What Causes Powdery Mildew?
Powdery mildew is made up of many, many microscopic spores. Spores are carried by the wind and land on new plant hosts. If the conditions are right, the powdery mildew can germinate and infect the plant. Unfortunately, the conditions that are best for your Crape Myrtles are also those where powdery mildew thrives. That’s why Crapes are so frequently affected by this disease.
Powdery mildew does best in warm temperatures with some shade, though the spores are sensitive to extreme temperatures (above 95 degrees) and direct sunlight. The disease thrives and spreads most easily when conditions are damp and humid. So, Crape Myrtles that are overcrowded, improperly pruned, or experience poor air circulation are most at-risk for serious problems.
How to Get Rid of Powdery Mildew
The best method for controlling powdery mildew is prevention. Crape Myrtles planted in full sun are less likely to provide the shady conditions the fungus needs to survive and thrive. It’s also important to remove shoots and suckers from around the base of your Crape Myrtle, as this new growth provides an ideal location for powdery mildew to take hold.
Once suckers become infected by powdery mildew, the fungus can quickly spread to the other parts of the plant as the shoot grows. So, you’ll want to remove them as soon as possible. To learn all you need to know about your Crape Myrtle’s shoots and suckers, you can check out this article dedicated to the topic.
Best Chemical Options
To treat powdery mildew that is very advanced, you may need to try a chemical option like a synthetic fungicide. We always recommend trying a more natural solution first, but there may be instances where you need a more potent treatment. Fungicides work best when they’re applied early, so you should treat your Crape Myrtle at the earliest sign of disease.
Myclobutanil is a synthetic fungicide sold under common names like “Immunox.” Spectracide makes this product available in a ready-to-use formula or concentrate. Other brands include Ferti-lome F-Stop Lawn & Garden Fungicide Concentrate and Monterey Fungi-Max. No matter which brand you go with, all these fungicides work both to eradicate to kill off existing powdery mildew and help protect against future problems.
If the powdery mildew growth becomes too extensive, it’s probably too severe for fungicides that provide protection only, and you’ll need an eradicant to deal with the problem. Fungicides work through direct contact with the growth, so you’ll need to treat all areas of the plant thoroughly. As your Crape Myrtle develops new growth, you’ll need to do additional treatments to protect the young foliage.
In some cases, you may need to reapply the fungicide every week to ten days until the weather changes and the fungus growth subsides. However, these chemical treatments are really only necessary when the disease has grown beyond just a mild or localized case. With small infections or when the disease is just starting, you should try using one of the natural treatments first.
Best Natural Options
In addition to improving your plant’s overall health, there are a few other natural methods you can use to help prevent or treat powdery mildew.
Horticultural oils and Neem oil can be very effective in preventing powdery mildew and may save you from having to apply so many chemicals to your landscape; plus, they won’t harm pollinators or other beneficial insects.
Ensuring ample sunlight and good airflow are essential to keeping the fungus at bay.
Selective pruning is an important practice for the overall maintenance of your Crape Myrtle. This involves removing branches methodically to open up the tree’s canopy and improve its shape or to remove any diseased, crossed, or rubbing branches. There’s a lot of misinformation out there when it comes to pruning Crape Myrtles, but some trimming is necessary. To learn exactly how and when to prune your Crape Myrtles, check out this article.
In addition, some cultivars are resistant to powdery mildew. If you’re thinking of adding a new tree to your landscape or looking to replace an existing plant, you should consider one of these resistant varieties:
- Tonto
- Muskogee
- Acoma
- Sioux
- Tuskegee
- Cherokee
- Hopi
- Catawba
If prevention fails and you find yourself battling a powdery mildew outbreak, there are a couple of natural fungicides you could try. Neem oil and other horticultural oils, jojoba oil, sulfur, and potassium bicarbonate have been effective for treating powdery mildew in some cases, as long as they’re used correctly.
Don’t apply oils or sulfur when temperatures are over 90° or when the Crape Myrtle is water-stressed. If you also treat with a sulfur spray, always wait at least two weeks before applying an oil treatment; otherwise, you may damage the plant.
Sulfur treatments are typically only effective if you apply them to your Crape Myrtle before the fungus appears on the plant.The best products for this use include those formulated specifically for lawn and garden use, like Safer Garden Fungicide.
A home remedy you can try is mixing one gallon of water with three tablespoons of horticultural oil and three tablespoons of potassium bicarbonate. If you don’t have potassium bicarbonate, you can substitute sodium bicarbonate (baking soda).
Putting It All Together
As with most other pests and diseases, prevention is key when it comes to battling powdery mildew. This fungus thrives in shaded, warm conditions with poor air circulation. Planting your Crape Myrtle in the right spot where it will get plenty of sunlight will be your best defense against powdery mildew.
If you find that this fuzzy foe has taken hold of your plant, don’t fret. There are plenty of treatment options, from store-bought antifungals to our old faithful – Neem oil.
In any case, selective pruning and removing your Crape Myrtle’s suckers and shoots is another important step to prevent the development and spread of powdery mildew. So, take the time to do a little routine maintenance each year, and it can save you from having to deal with this unsightly disease come springtime.