If youre really concerned about your powdery mildew and safety, your
best route is the old baking soda solution. Unfortunately, I don't
know the recipe off the top of my head. I think its about 2% B.S. but
check. Neem oil is another option, but can become phytotoxic if the
temperature gets to high. Appropriate fungicides include Bayleton,
Funginex, Halt and Banner, but check your labels because Banner may not
be labelled for for powdery mildews of crepe myrtle and would be
Hope this helps some. By the way, the fungus infecting your tree is
pretty cool, too. Under the scope, it looks like a multi-tentacled
"invasion of the body snatcher-type" alien.
Dept. Plant Pathology and Microbiology
Texas A&M University
"Let rot proclaim its revolution!"
13. Crepe Myrtle
14. crepe myrtle