...deadheading the old blooms prevents un-opened flower buds from getting any fungal infections.
With all this rain, sometimes the old flowers close up and leave wilted petals incased in the flower's sepals. This is a perfect place for moulds, and fungal spores to develop.
The smaller varieties like this one, you just pinch back with your fingers. With the dinner plate varieties, I would use a set of pruners or scissors to cut them back.
Enjoy endless blooms, with a good water soluble feed every two weeks: compost tea, fish emulsion or 10:52:10.