Dieback on ornamental pear trees

thebakersindedham

Hi everyone 

I wonder if anyone can identify the disease I appear to have on my recently planted ornamental pear trees. 

The leaves have died back and the underside appears to have a white substance on them see pictures attached. 

Some perenial plants directly underneath the pear trees also seem to have been affected. 

Does anyone know what this may be and how to treat it?

many thanks for any advice.

PB