I would opt for a lower toxicity approach. Tebuconazole is classified as level III which means slightly hazardous. Plus I saw no mention of it controlling powdery mildew although it does treat fusarium wilt (a serious disease) on cereal crops. See the link below to find out what I read.

I always used baking soda dissolved in water in my hose end sprayer for powdery mildew on my crepe myrtles.

I found this suggestion at the Growing a greener world website:
Use this recipe to make your own solution.Mix one tablespoon of baking soda with a teaspoon of dormant oil and one teaspoon of insecticidal or liquid soap (not detergent) to a gallon of water. Spray on plants every one to two weeks.

I forgot how to make this clickable, but a copy and paste will work too:
http://www.growingagreenerworld.com/controlling-or-eliminating-powdery-mildew/

I never used anything other than baking soda and water and it seemed to help. I think that it is more unsightly than an actual danger to your tree. I found lots of no tox options on the website, like vinegar and mouthwash, to provide two examples.

Good luck with whichever route you take :-)

Here is a link that might be useful: Tebuconazole

Thanks! My worry is that I just closed on the house in January and this tree is one of the big reasons that I bought it. I will look into a more natural way to handle it (my usual way to go at things, but in this case I am willing to be more drastic). Thanks for the info, I am going to dig into it and see if it looks like this is a good option for me. This pool is much of the shade over my pool and I have a very fare skinned lass that will not be able to use the pool much if we lose this tree.

You will not lose your tree to powdery mildew. It's just not a fatal disease, although not very pretty :-)

Think of the drip of whatever you use into the pool where you and your family swim, please! You mentioned that it overhangs your pool.

This post was edited by pkponder on Thu, Jul 11, 13 at 19:20

Thanks pkponder, No matter what I spray, the pool will be covered so there will be no runoff in it. The pool is my baby and I tend the chemicals in that more carefully than I tend any other part of the house/yard. I don't want my kids around chemicals that they don't have to be exposed to (thus my general lean towards natural methods). I take care of my own pool because I believe the pool companies are forced to over chemical the pool since they come but once a week. I am able to expose my kids to much less by tending it every day. No spikes in chemical levels.