You must have a disease susceptible crape myrtles, as the National Arboretum cultivars are all very resistant. ;-( Unnamed varieties or seedling crape myrtles can be VERY prone to this fungus.

First of all, there are some cultural things that you should pay attention to. Avoid topping your crape myrtle, as that forces plants to produce enormous unnatural growth spurts so attractive to PM. Avoid excessive nitrogen fertilization. Thin out your plant with proper pruning cuts to improve sunlight penetration and air circulation. Keep all sucker growth pruned from the trunk.

Sulfur based fungicides can be very effective, but you must read and follow directions for use. Also, neem oil has been reported to be helpful, super fine horticultural oils, and baking soda sprays. Be careful that you don't use the sulfur sprays within two weeks or so of an oil application. The label will have that on it.

Remove the old mulch once you've got the PM under control and replace with fresh. If you haven't mulched at all, do so.

Sounds like a lot of work, but in truth.......PM outbreaks can be almost entirely avoided. It's much easier to prevent than to have to treat your plant for the entire season.

Wow, thank you for the excellent info.

Or you can be a complete slacker like me and ignore it completely. Eventually the tree will be 20 feet tall and you won't be able to see it anyway. I'd like to say it's called tough love, but really it's unexcusable indifference.

Hey, we have suwanee, sugarhill and buford on the same thread....

I had bad PM on one of my crepe myrtles afew years ago. My neighbors had allowed their shrubs near the CM to get very high and they were blocking out the morning sun. Thankfully they've cut them lower and the CM has gotten higher, as sugarhill suggested.

http://aggie-horticulture.tamu.edu/plantanswers/trees/crapemyrtle/crape_myrtle_varieties.html is a good website that lists characteristics of many crapemyrtle cultivars, including levels of powdery mildew resistance

I have the powdery mildew on just the buds of my crepe myrtle tree. It should be in full bloom about now and I am wondering if it will bloom this year.