A number of factors could cause leaves to drop. Can you post a picture? These plants must have only dappled light, like under a deciduous tree -no direct sun. Did you have a cold snap? Too much fertilizer is another reason for leaf cast. How long have you had this plant? If the whole plant is yellowing, you should just replace it. They are short-lived plants anyway.

Hi there Woodlands7. I absolutely love this shrub which I had for about 18 years. It was fabulous until last year when the leaves turned yellow and it died this year. If you have had it a long time it could have come to the end of it's life.

Merin - I think I recall reading that these are short lived shrubs and only live 10-20 years. Nothing can be done to change it.

I had this happen with a newish daphne, and Epsom salts helped it, I think it was about 1 tbsp per 2 gallon can, but don't trust my memory! Someone will know better than me. I also sprayed it with seaweed solution. It's doing well now.

That ratio sounds about right. You can also use Epsom salt solution as a Foliar spray. It's great for tomato plants.