Crape Myrtle being attacked by mold

Question: Hi,

I have a young Crape Myrtle tree that I planted about 5 years ago. It's in a mostly sunny spot on a slight hill in clay soil.  Last summer at the end of its blooming season, the flowers became covered with what looked like white mold. I sprayed them with a copper soap called "Nature's Care Garden Disease Control" by Miracle Gro, but it didn't seem to do anything. 

This year, the same mold has started at the tips of the branches already even before the flowers are blooming. Each day it seems to  move further down the tree. I hope the attached photos are helpful.  

Thanks so much for any advice you can give!

Best regards,
Elizabeth

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube.  Replied June 13, 2023, 7:30 PM EDT
response: Hello and thank you for your question.   The white mold on your crape myrtle is powdery mildew, a very common fungus in our climate. Crape myrtles are very susceptible to it, and the dry, warm days followed by cool nights we've had in the past month are perfect for spreading it.  No fungicide is needed for a powdery mildew infestation, as once it is present it is very difficult to eradicate and fungicides are generally used as preventatives. Caution should be used when applying a fungicide as well, as they can adversely affect pollinators. Fungicides should never be sprayed on flowers or buds. If the infestation is very severe, horticultural oil or neem oil can be used to limit the spread and attempt to eradicate the mildew. Be cautious to follow the directions for appropriate dilution rates (if using a concentrate), never spray when temperatures are over 90 degrees F, do not spray drought stressed plants, and always give at least 2 weeks time before applying oil if you have used a sulfur based product, as plant injury can occur.   If the tree is in part sun instead of full sun, or if it does not get adequate air flow due to a tree line or structures nearby, the mildew will be worse. While an eyesore, it should not hurt the overall health of the crape myrtle BUT a heavy powdery mildew infestation will stunt growth some and distort or prevent some flower buds from opening. Those very mildewed branches can be pruned off, if desired.  If you are open to replanting your crape myrtles, the best preventative measure for powdery mildew with crape myrtles is planting resistant varieties. Generally those with Native American names, e.g., ‘Catawba,’ ‘Cherokee,’ ‘Hopi,’ etc., are mildew resistant. All those are introduced by the US National Arboretum, just scroll down to "Lagerstroemia" for the full list on that page.  I hope some of this was helpful. Please let us know if there's anything further we can assist with.

responder: The Question Asker Replied August 10, 2023, 3:27 PM EDT
response: Hello,A belated thank you for this information. It was very helpful. I will not use fungicide in the future. The crape myrtle branches grew past the powdery mildew and are currently in full bloom. If the mildew becomes more of a problem, I'll look at replacing the tree with one of the resistant varieties you suggested. Thanks again,ElizabethOn Tue, Jun 13, 2023 at 7:30 PM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 10, 2023, 4:23 PM EDT
response: You're welcome.