Definitely not burn or dispose of in your wheelie bin. If you put in compost you will be introducing into your soil!

So glad i saw this question. One of my plants has powdery mildew on it and i most certainly would have put it in the compost bin. Pheeeew!

Powdery mildew is a fungus and normal garden compost is not going to be hot enough to kill it. Any diseased plant tissue should be destroyed either by burning on putting in the wheelie bin to prevent further infection. This is particularly vital with blight.