What’s wrong with my rose

I bought a new patio rose and within a couple of weeks I noticed the leaves looking like this , I assumed a fungal disease and have spent the last week pulling off all the effected leaves and spraying with baking powder. Every time I look at it I find leaves that need pulling off, it's soon going to have no leaves left.
What can I do?!

 

Yes, it's rose black spot, a fungal disease. There are some suggestions for controlling it on the link.

 

Baking powder is different to baking soda.
I find American sites call bicarbonate of soda, baking soda.
Baking powder is something different.

 

Sodium bicarbonate (bicarbonate of soda) is what you require. Its known to correct acidity and control fungus in both plants and humans

 

Ahh thank you, that makes sense. I will get some.