Sandy if the leaves were older then they were probably getting ready to die off....it's the new/newer leaves that should cause alarm. BUT it's not out of the question that the Neem might have excellerated their demise.
Eric, I think I added 1 teaspoon or 1.5 teaspoons per gallon and I used a systemic. I think the Enstar website tells you what insecticides it is compatible with.