I planted a crape myrtle about three years ago and every summer the leaves get a powered meldow what should I do about at

Too much damp weather. Too little light. The only thing that will take care of it is sunshine and warm weather. Hang in there, summer is just around the corner.

We have used liquid fungicide and sprayed our trees when affected by mold.

Do you know the variety? Some are more prone to mildew. They do need plenty of sun and air circulation to help fight this disease. (a fungus, Erysiphe lagerstroemiae)

Best to chose a mildew-resistant type. Almost all of the newer ones are resistant, like the ones named after tribes of native Americans.

I read online some suggestions of what to use: To control, use a spray in early summer with neem oil, horticultural oil, Natria Disease Control, Daconil, or Immunox. The first three are natural products. You most likely will have to spray more than once.

Ahh ! Ha !
Blast it with water hose nozzle.
It will rinse off.
Do it early enough that the water will dry before evening.
Dew causes mildew.
Repeat as necessary.
Mildew wont hurt tree.
😎😎😎

This is not the type that will rinse off, the Erysiphe lagerstroemiae even suggests that it's specific to Crape myrtles (Lagerstroemia) and yes, it can cause damage. "Heavily infected flowers may fail to open. Infected parts of the plant are usually distorted and stunted. " Grown for their stunning blooms, it's quite disappointing if they fail to open.

According to this site: http://www.clemson.edu/extensi...

"Powdery mildew is one of the most common problems of crape myrtle, and it is caused by the fungus Erysiphe lagerstroemia. Patches of white to grayish powdery growth occur on the surfaces of leaves, flowers and new shoots. Heavily infected flowers may fail to open. Infected parts of the plant are usually distorted and stunted. The disease is most serious in shady, damp locations, especially where plants are crowded and air circulation is poor. Development of the fungus is favored by high humidity at night and dry, mild daytime conditions, as often occurs during the spring and fall.
Prevention & Treatment: The most effective control measures include locating plants in full sun, removing sprouts from the base of the plant and planting resistant varieties. Susceptible varieties of crape myrtle should be avoided. Removing diseased twigs and branches may be possible, if only a few shoots are infected. Remove sprouts (suckers) at the base of the plant as they occur, since they are very susceptible to powdery mildew. Once these sprouts become infected, the fungus easily spreads to the upper portions of the plant.

There is a nice long list of suggested plants to grow as well as ones to avoid.