I have 2 Muskogee Crape Myrtles planted near my house that grow like weeds. However, every summer, the trees get covered in little brown spots, and the leaves yellow and fall. I am pretty sure this is Cercospora Leaf Spot. I really makes the trees look ugly, and it defoliates more than 50% of the leaves and litters the sidewalk and driveway with dead leaves. It also really diminishes flowering.

They get plenty of sun and good air circulation, so I really don't know why this happens every year. I have sprayed fungicide every year after I notice the fungus appearing, but it doesn't seem to help. This year I want to try a systemic BEFORE the problem starts in hopes that I can finally avoid this problem. It is getting so bad I am seriously considering cutting the trees down, which is very hard since they are such an integral part of the landscaping in front of my house.

Please recommend a pre-emergent that will put an end to this terrible problem.