Powdery Mildew on Crape Myrtle - Ask Extension
How do I get rid of Powdery Mildew on young Crape Myrtle?
Knowledgebase
Powdery Mildew on Crape Myrtle #839231
Asked July 06, 2023, 9:31 AM EDT
How do I get rid of Powdery Mildew on young Crape Myrtle?
Howard County Maryland
Expert Response
Please help me get rid of Powdery Mildew on a young Crapee Myrtle that gets afternoon sun.
All the new shoots are affected. I sprayed with a Baking soda solution last night and it helped some, but not completely. How often can I spray so I don't damage tree? I Just cleaned around he tree so that air ciculates since this tree likes it drier rather than wet and there should not be any plantings next to the bottom of the tree. Besides the powdrey mildew I would like other information that can help me take care of Crape Myrtle. What spray can you recomend?
Thank you.
The simplest approach, assuming the mildew-infected branch tips are within reach, is to trim them off. Fungicide cannot cure existing infection, nor will current symptoms disappear, but it might help prevent a resurgence. Weather conditions are very conducive to powdery mildew outbreaks this time of year and crapemyrtle (plus a wide variety of other plants) are common host plants for fungi in that group. The mildew on the crapemyrtle will not necessarily infect unrelated plants, so you don't have to worry about cross-contamination of nearby plantings. If mildew appears on other plants anyway, this is simply because these fungi all require the same weather conditions to thrive, so outbreaks overlap.
We discourage fungicide use when an infection does not seriously impact long-term plant health, as is the case here. Plus, as a plant whose blooms can attract pollinators (even though as a non-native they are not nearly as popular as other plants), using a fungicide may risk harming them, even though its function is not to kill insects. If you were to spray, do not treat any open flowers or flower buds, or cut off any flowers that are exposed to a fungicide spray. If any current growth is budded and infected with mildew, cut if off as infected buds don't usually open properly and crapemyrtle tends to rebloom readily.
Although baking soda (sodium bicarbonate) can be an ingredient in some organic fungicides, we do not recommend the use of household baking soda as a home remedy. The sodium bicarbonate dilution in registered pesticides is tested on plants for efficacy (and potential harm to foliage, another risk of home remedy substitutes) and may also be combined with other ingredients that help it function more effectively. If you attempt to use a fungicide to manage this fungus outbreak, select a labeled fungicide instead, organic or otherwise. We do not have a specific ingredient recommendation since many products work decently well on powdery mildew as long as they are applied as directed, which tends to involve repeat spraying as the label details.
As for general crapemyrtle care, there aren't many serious issues that plague them. Crapemyrtle Aphid is very common but rarely requires treatment. Crapemyrtle Bark Scale is more serious and harder to treat; information about management options are given in the linked page (plus the page it links to about general scale management). Do not treat preventatively for this pest; it should be present and confirmed before beginning any treatments. Several kinds of fungal leaf spot can affect the plant's foliage but these tend to be minor and more common when the foliage is wet often, such as from irrigation (more typical of nursery stock than in-ground plants in home landscapes unless they are a dwarf/miniature variety that stays short).
Grow crapemyrtle in full sun (6-8 or more hours of direct summer sun), though they will tolerate less but flower less abundantly in that case. Soil should drain well, and while these plants have good drought tolerance, they should be monitored for watering needs if the weather is dry for long periods, as it was earlier this year for most Marylanders. Stress from drought won't necessarily manifest as wilting but stressed crapemyrtle can be more vulnerable to pest or disease issues. They should not need regular fertilization (especially if growing near a lawn which is fertilized annually) and spent flower clusters can be trimmed off to encourage faster and more abundant rebloom, though some varieties rebloom well enough on their own without this step.
Miri
We discourage fungicide use when an infection does not seriously impact long-term plant health, as is the case here. Plus, as a plant whose blooms can attract pollinators (even though as a non-native they are not nearly as popular as other plants), using a fungicide may risk harming them, even though its function is not to kill insects. If you were to spray, do not treat any open flowers or flower buds, or cut off any flowers that are exposed to a fungicide spray. If any current growth is budded and infected with mildew, cut if off as infected buds don't usually open properly and crapemyrtle tends to rebloom readily.
Although baking soda (sodium bicarbonate) can be an ingredient in some organic fungicides, we do not recommend the use of household baking soda as a home remedy. The sodium bicarbonate dilution in registered pesticides is tested on plants for efficacy (and potential harm to foliage, another risk of home remedy substitutes) and may also be combined with other ingredients that help it function more effectively. If you attempt to use a fungicide to manage this fungus outbreak, select a labeled fungicide instead, organic or otherwise. We do not have a specific ingredient recommendation since many products work decently well on powdery mildew as long as they are applied as directed, which tends to involve repeat spraying as the label details.
As for general crapemyrtle care, there aren't many serious issues that plague them. Crapemyrtle Aphid is very common but rarely requires treatment. Crapemyrtle Bark Scale is more serious and harder to treat; information about management options are given in the linked page (plus the page it links to about general scale management). Do not treat preventatively for this pest; it should be present and confirmed before beginning any treatments. Several kinds of fungal leaf spot can affect the plant's foliage but these tend to be minor and more common when the foliage is wet often, such as from irrigation (more typical of nursery stock than in-ground plants in home landscapes unless they are a dwarf/miniature variety that stays short).
Grow crapemyrtle in full sun (6-8 or more hours of direct summer sun), though they will tolerate less but flower less abundantly in that case. Soil should drain well, and while these plants have good drought tolerance, they should be monitored for watering needs if the weather is dry for long periods, as it was earlier this year for most Marylanders. Stress from drought won't necessarily manifest as wilting but stressed crapemyrtle can be more vulnerable to pest or disease issues. They should not need regular fertilization (especially if growing near a lawn which is fertilized annually) and spent flower clusters can be trimmed off to encourage faster and more abundant rebloom, though some varieties rebloom well enough on their own without this step.
Miri
Dear Miri,
Thank you for that wealth of information. This particular Crape Myrtle had Powdery Mildew on it last summer as well. Is that's why it re-appeared again this year since you are saying that fungicide can not cure existing conditions? Will it always stay with the tree unless it is cut away? The tree actually grew a foot since last year.
If I cut away the branches that have Powdery Mildew on it, this cute little tree will then look like a bush when it grows out. What do I do with the top of the tree, can I spray the top some more so it will continue to grow straight up rather than sideways? I am so sorry this has happened. The tree is in the front of my house and I planted it to replace a an American Dogwood that died. It seems you think the Crape Myrtle is not the best tree to grow in this area. Can you recommend another tree I can plant in the front of my house that grows fairly fast and doesn't grow too large, yet would be a good tree in the front of my house? I bought this tree at the Home Depot 2 years ago along with another Crape Myrtle that gets more sun and that one is doing quite well. I can not afford to buy a larger tree and I'm the one that will plant it as well at an age of 81. Are there people from the Extension Service that will come out and help homeowners with selection and location of trees? Sometimes there are free give-always of trees by local organizations, but the selections are limited. Last year I got a Black Gum, but it's a large tree and I'm not sure how it develops. This year some leaves dried up and I have never seen that on a tree before. I planted it in an area that was moist, but that dried up this summer. They also give out River Birches, but they don't live forever in this area. I would appreciate you helping me with my additional questions.
Thank you so much.
With appreciation,
Froydis
Hello Froydis,
Powdery mildew typically shows-up each summer on most, if not all, varieties of crapemyrtle...it's just one of their vulnerabilities combined with the fact that summer weather is very conducive to mildew growth because of our high humidity. Spores might remain on the plant over the winter but they can also reside on fallen infected leaves that shed in autumn or they can blow-in from further away the following year. This is the main reason fungicide treatments, if warranted, need to be applied yearly because each new season begins a new window of opportunity for an infection to take place. Fortunately, even though we consider powdery mildew to be an eyesore, from the perspective of long-term plant health, it is rarely a serious issue and does not require treatment to save the plant. Treatments are only for our benefit in this case, helping to reduce obvious symptoms plus allowing more blooms to open normally if mildew is attacking the closed flower buds. If pruning will alter its shape too much, you do not need to prune mildewed tips off, though it shouldn't be very much that would be trimmed in that case anyway -- just the most heavily-affected tips with white-gray foliage or buds covered in mildew. It's hard to assess how serious or not the infection is without photos.
We did not mean to imply crapemyrtle are not worth growing when we mentioned the issues that might arise; we were merely trying to address your request for "other information that can help me take care of Crape Myrtle." Knowing what possible ailments can affect these plants will help you be aware of what to look for and realize what does or does not need treating if it's discovered. (Aphids - no, scale - probably.)
There are plenty of other trees, native or not, that do well in our area, but none are without their weaknesses towards certain conditions; everything can contract something if conditions are right. Still, despite a variety of insects and leaf-spot diseases or other infections afflicting trees, relatively few are serious enough to warrant the efforts of treatment. Plus, selecting a varieties with pest or disease resistance, if they exist for the type of tree being considered, also helps improve their vigor and appearance.
Fast-growing trees tend to mature large (multi-story shade tree size) but exceptions include the large-growing varieties of crapemyrtle (which can still reach 20-30 feet, but this is considered small to medium for a tree). We actually discourage gardeners from buying large trees with the intent of trying to get a jump-start on growth and maturity because this can backfire -- larger trees transplant with more stress, so younger trees actually have an easier time adjusting and their growth usually catches-up well with older counterparts so that after a few years there is no major difference in their size. They're also much easier to plant when younger, since the planting hole can be smaller.
Extension doesn't perform site visits but you may be able to discuss in person (with a photo of the planting site, which can be helpful) ideas for tree selection and placement with Master Gardeners at a local plant clinic, or with someone in your county Extension office. We are not aware of free consultation services but there might be some sources for help either of the folks above are familiar with.
Young trees, especially moisture-loving species like Black Gum and River Birch, need to be monitored for watering needs during their first few years in the ground as their roots get established. During drought, like we've been experiencing in most of Maryland for most of this year so far, a thorough soaking of a young plant might need to take place once every week or so, depending on factors like the soil drainage. Feeling the soil about six inches deep to judge when it's becoming dry enough to need rehydrating is the main way we recommend doing this, since relying on surface moisture can be misleading as to how deeper roots are faring, and heavy rains don't always soak in as much as we think they should. Our Watering Trees and Shrubs web page provides more information. For example, a tree-watering bag placed around the trunk of a young tree can help greatly with making it easier to keep it watered.
No tree lives forever (even long-lived trees like oaks in suburbia tend not to live very long compared to their wild forest counterparts due to chronic stresses), but River Birch is not considered to be short-lived; gardeners should have them thrive for at least several decades. They have limited tolerance for drying out, but even some leaf shed during a hot, dry spell in summer isn't fatal for them as long as they can be watered on occasion if droughts persist. Other birch species do struggle more in our hot climate, since they prefer cooler summers, but River Birch in particular does pretty well in Maryland.
It's hard to recommend an alternative tree species without seeing the site conditions in a photo or knowing how much summer sun it receives, how moist or dry the soil tends to stay, what limits there are on mature size (you mention not wanting it to get "too large," but "large" means different sizes to different people) and if there are any obstacles like power lines to worry about. Whether or not you have deer visiting the yard is another consideration since they can consume foliage (while it's still in reach at least) and bucks can rub antlers on young trees in autumn, which causes serious bark damage. We can share some ideas below, though.
Where possible, we encourage gardeners to plant native species for the benefit of wildlife. There are several native trees whose flowers or other features are showy but they will not have very rapid growth since they don't mature very large. For example, if the site is full sun or mostly-sun and the soil not too wet:
Miri
Powdery mildew typically shows-up each summer on most, if not all, varieties of crapemyrtle...it's just one of their vulnerabilities combined with the fact that summer weather is very conducive to mildew growth because of our high humidity. Spores might remain on the plant over the winter but they can also reside on fallen infected leaves that shed in autumn or they can blow-in from further away the following year. This is the main reason fungicide treatments, if warranted, need to be applied yearly because each new season begins a new window of opportunity for an infection to take place. Fortunately, even though we consider powdery mildew to be an eyesore, from the perspective of long-term plant health, it is rarely a serious issue and does not require treatment to save the plant. Treatments are only for our benefit in this case, helping to reduce obvious symptoms plus allowing more blooms to open normally if mildew is attacking the closed flower buds. If pruning will alter its shape too much, you do not need to prune mildewed tips off, though it shouldn't be very much that would be trimmed in that case anyway -- just the most heavily-affected tips with white-gray foliage or buds covered in mildew. It's hard to assess how serious or not the infection is without photos.
We did not mean to imply crapemyrtle are not worth growing when we mentioned the issues that might arise; we were merely trying to address your request for "other information that can help me take care of Crape Myrtle." Knowing what possible ailments can affect these plants will help you be aware of what to look for and realize what does or does not need treating if it's discovered. (Aphids - no, scale - probably.)
There are plenty of other trees, native or not, that do well in our area, but none are without their weaknesses towards certain conditions; everything can contract something if conditions are right. Still, despite a variety of insects and leaf-spot diseases or other infections afflicting trees, relatively few are serious enough to warrant the efforts of treatment. Plus, selecting a varieties with pest or disease resistance, if they exist for the type of tree being considered, also helps improve their vigor and appearance.
Fast-growing trees tend to mature large (multi-story shade tree size) but exceptions include the large-growing varieties of crapemyrtle (which can still reach 20-30 feet, but this is considered small to medium for a tree). We actually discourage gardeners from buying large trees with the intent of trying to get a jump-start on growth and maturity because this can backfire -- larger trees transplant with more stress, so younger trees actually have an easier time adjusting and their growth usually catches-up well with older counterparts so that after a few years there is no major difference in their size. They're also much easier to plant when younger, since the planting hole can be smaller.
Extension doesn't perform site visits but you may be able to discuss in person (with a photo of the planting site, which can be helpful) ideas for tree selection and placement with Master Gardeners at a local plant clinic, or with someone in your county Extension office. We are not aware of free consultation services but there might be some sources for help either of the folks above are familiar with.
Young trees, especially moisture-loving species like Black Gum and River Birch, need to be monitored for watering needs during their first few years in the ground as their roots get established. During drought, like we've been experiencing in most of Maryland for most of this year so far, a thorough soaking of a young plant might need to take place once every week or so, depending on factors like the soil drainage. Feeling the soil about six inches deep to judge when it's becoming dry enough to need rehydrating is the main way we recommend doing this, since relying on surface moisture can be misleading as to how deeper roots are faring, and heavy rains don't always soak in as much as we think they should. Our Watering Trees and Shrubs web page provides more information. For example, a tree-watering bag placed around the trunk of a young tree can help greatly with making it easier to keep it watered.
No tree lives forever (even long-lived trees like oaks in suburbia tend not to live very long compared to their wild forest counterparts due to chronic stresses), but River Birch is not considered to be short-lived; gardeners should have them thrive for at least several decades. They have limited tolerance for drying out, but even some leaf shed during a hot, dry spell in summer isn't fatal for them as long as they can be watered on occasion if droughts persist. Other birch species do struggle more in our hot climate, since they prefer cooler summers, but River Birch in particular does pretty well in Maryland.
It's hard to recommend an alternative tree species without seeing the site conditions in a photo or knowing how much summer sun it receives, how moist or dry the soil tends to stay, what limits there are on mature size (you mention not wanting it to get "too large," but "large" means different sizes to different people) and if there are any obstacles like power lines to worry about. Whether or not you have deer visiting the yard is another consideration since they can consume foliage (while it's still in reach at least) and bucks can rub antlers on young trees in autumn, which causes serious bark damage. We can share some ideas below, though.
Where possible, we encourage gardeners to plant native species for the benefit of wildlife. There are several native trees whose flowers or other features are showy but they will not have very rapid growth since they don't mature very large. For example, if the site is full sun or mostly-sun and the soil not too wet:
- American Fringetree (Chionanthus virginicus)
- Eastern Redbud (Cercis canadensis) - not very long-lived but it should thrive for at least 20-30 years; typical flower color is pinkish-violet but varieties exist that are white or more rosy-pink; some have colorful foliage as well; for a tree that doesn't get much over 20 feet high, growth is relatively fast
- Serviceberry (Amelanchier) - sometimes a fungal rust disease causes orange spots on the foliage but it's usually not drastic or debilitating and, unless you were intending to harvest its edible berries, the impacts from the rust are fairly inconsequential and it won't keep trees from flowering; like the redbud, mature size isn't too big but growth can be relatively fast considering its smaller stature
- Green Hawthorn (Crataegus viridis variety 'Winter King')
- Bigleaf Magnolia (Magnolia tripetala, though Magnolia macrophylla or Magnolia ashei may be a little easier to find) - big leaves giving it a tropical look but the flowers are also large, even for a Magnolia
- Cucumbertree Magnolia (Magnolia acuminata) - more modest-sized leaves and flowers that are a more subdued greenish-yellow
- Sassafras (Sassafras albidum) - may be harder to find and slow at first, becoming a bit faster as it matures
- Sweetbay Magnolia (Magnolia virginiana) - can be shrubby-looking when young (this depends on how the nursery grew them, whether multi-trunked or single-trunked); might keep a few leaves in winter but it's not truly evergreen here in Maryland; quite fragrant
- Pawpaw (Asimina triloba) - also tolerates shade well; might produce multiple trunks over time; a lone tree without a pollinator is unlikely to bear fruit if you don't want any, though wildlife is happy to eat it anyway
- American Hornbeam (Carpinus caroliniana)
Miri
Hello Miri,
Thank you again for providing me with so much in depth information. I know a lot more about the Crape Myrtle, thanks to you. I had no idea that the Powdery Mildew was so prevalent on the Crape Myrtle having 3 pretty large healthy Crape Myrtles that never had any Powdery Mildew. They all grow on drier grounds and the climate may have been different when I planted them. I may leave the Crape Myrtle alone for now, certainly not cut off the top. New growth is coming out from the Powdery Mildew. I'm glad that leaving them alone may be ok and that they are not damaged forever.
Thank you so much for providing me with suggestion on other trees to plant. I googled them all. I found the information on planting trees very helpful, that a smaller tree will survive better and eventually catch up in height with a tree that was larger when planted. I am also glad to hear that the River Birch will do well in this area if watered correctly. How to water was also helpful. I certainly have watered often and close to the trunk.
I am grateful that I contacted the Maryland Extension service. Thanks to you, Miri, I have learned a lot about the Crape Myrtle and how to care for it as well as other useful information about trees. Last year I contacted you about using Barricade to control Japanese Stiltgrass. My lawn has much less Stiltgrass this year, however, I will put down the Barricade again next spring.
Thank you very much for your help.
With Appreciation,
Froydis
You're welcome!
Unless they are all the same variety, it's possible the other crapemyrtle plants have better resistance to mildew than the newer one; there are so many varieties on the market now (around a hundred or more) that not all are on equal footing with regards to disease tolerance. It's good that they're faring well and will likely not be overly bothered by any mildew outbreaks in the future.
Miri
Unless they are all the same variety, it's possible the other crapemyrtle plants have better resistance to mildew than the newer one; there are so many varieties on the market now (around a hundred or more) that not all are on equal footing with regards to disease tolerance. It's good that they're faring well and will likely not be overly bothered by any mildew outbreaks in the future.
Miri
