It isn't just my begonias , something is also killing my dahlia'a! Attaching a photo . Also verbena just died. I have about 16 huge pots in my patio and porch and all of a sudden , they are dying .thank you!
I would say we would need more information than a picture of two old (dahlia) leaves. How wet are your pots? How much sun do they get? How dry do you let your pots get? What kind of begonias are they? When did you get the begonias (this year?) Did they grow at all or slowly die down? Did you remove old dead leaves as they fell or turned yellow? A picture might help too.