This question has bothered me since I started gardening. We spend a lot of time removing fallen leaves, then either take them to the municipal compost facility or make a compost pile, hopefully really compost them, and put them back. If the leaves were spread about and left on the garden, mixed with a bit of true compost, without doing a total removal and replacement with "compost", will they compost in place, and will they really increase disease in plants [I can see that fallen rose leaves and others with mildew or other disease could be a problem]. I am assuming the answer will be yes, the leaves have to compost. But what happens to the plant infectious diseases which are part of the leaves being composted? Killed by the composting process, or not?