Question
I get powdery mildew EVERY YEAR on the leaves of my three (3) crimson sentry maple trees. This powdery mildew stays on the leaves thru the entire summer. This year is the absolute worst I've seen -- all leaves are totally white with the powdery mildew, and leaves are beginning to wilt/dry up & fall off. I have used TruGreen ChemLawn tree service for years. Every year, TruGreen ChemLawn spray once a month beginning in early spring (around April 1) until the end of summer (into early November). The ChemLawn manager came to my home to evaluate my concern, and said the powdery mildew was the worst he had seen, & that he didn't have an answer for it. He thought it may have been caused by the heavy rainfall that we get every spring here in Michigan (Ann Arbor). ChemLawn use the same fungiside spray on all of my trees in my landscape, but whatever is being used is not working for my Crimson Sentry. Can you help me?

Answer
Since I do not know what TruGreen ChemLawn is using it would be hard to comment on if the fungicide they use is the best. Mildew varies by different species of plants so it may take a fungicides for mildew work on maple--the fungicide label would list maple as a species that it works on. Also mildew can become resistant to soma fungicides so changing the fungicide may also help. One thing I did notice was that with an agressive mildew the recommendation is treating every 7-14 days. Here is information on control of mildew and the fungicides that are recommended for maples:
Chemical control: Most are not labeled for use on trees to be used for syrup production. Fungicides will do best when used before symptoms develop. Few materials have good eradicant activity. Use at 7- to 14-day intervals; using shorter intervals when environmental conditions favor disease development.
Banner MAXX at 5 to 8 fl oz/100 gal water may be effective. 24-hr reentry.
Bayleton 50 T&O at 5.5 oz/275 to 550 gal water. 12-hr reentry.
Cygnus 50 WG at 1.6 to 3.2 oz/ 100 gal water plus a non-organosilicone spreader-sticker is registered for only a few maple species. Best used before symptoms develop. Do not use near Norway maples. 12-hr reentry.
Eagle 20 EW at 6 to 12 fl oz/100 gal water. Do not use treated trees to produce syrup. 24-hr reentry.
Heritage at 1 to 4 oz/100 gal water plus a non-silicone based wetter sticker. 4-hr reentry.
Immunox at 1 fl oz/gal water.  
Safer Garden Fungicide (Ready To Use 0.4% sulfur) throughly sprayed over the entire plant. Do not use when the temperature is over 85癋 or within a few weeks of an oil spray.  
Strike 50 WDG at 1 to 2 oz/100 gal water. 12-hr reentry.