Hi,
Lollie
I have had success with a mix of baking soda and insecticidal soap. It is 1 Tb per gallon for the baking soda and whatever the label directions call for with the soap. Be sure to thoroughly soak the infected leaves top and bottom. The soap helps the spray mix to stick and spread so don't be shy about getting everything wet. Keep cleaning up any fallen leaves and spray weekly as necessary.