can raspberry plants cause mildew in Crepe Myrtles?
I bought a Crepe Myrtle,var.Tonto, about 7 yrs ago.The only plant that has been added to that garden area are 5 Raspberry plants. Since planting them 3 winters ago, this Crepe Myrtle developed a very intense white mildew,and spraying has done nothing to control it ,even tho' I started to spray as soon as the leaves 1st appeared. I live in zone 7A, southern NJ.
I doubt if the powdery mildew on the crape myrtle is related to the raspberry plants, but its possible. The powdery mildew on crape myrtle is usually a different species from other powdery mildews on other plants.
The entire tree photo shows that the tree has been heavily pruned and rampant vegetative growth has resulted. That type of growth will be very susceptible to powdery mildew. Do light thinning and shaping and don't top the tree heavily. It takes acquired skills, you may want to hire a professional.
Try this fungicide for preventive treatments in the spring and summer: