In sams wrote:
Today I take a look and the
leaves all shows kind of a layer of ash, especially on the leaf edges
and on some part of the stem. Looks like fungus to me.


Welcome to the world of powdery mildew. There are plenty of fungicides
for it, ask at your local garden centre. Another remedy is a spray of
milk (1 part milk to 6 parts water) applied on a sunny day, which kills
it pretty quickly.