None. Powdery mildew rarely affects the health of a tree. The treatment of trees with a fungicide should be done by a licensed pesticide specialist, wearing protective gear. Fungicides have to be strong because fungi are hard to kill and treating a tree puts a lot of fungicide into the air and the respiratory zone of the applicator.
Your website recommends several fungicides. There are a number of commercial products. It seems homeowner treatment is encouraged. Do you have a favorite fungicide to use?
No I personally do not use fungicides because they are rarely very specific in what they kill and I am too lazy to treat something that only looks ugly. Years when powdery mildew is prevalent have the right conditions to promote powdery mildew infection of many plants. The fact sheet does provide information about fungicides that are effective. I cannot provide a personal opinion because I haven't tried any.