I've got rather large zucchini & squash plants that are ready to be pulled. They have some powdery mildew on them and I plan on washing them down are well as possible. Will I have a problem if I put them in our compost bin?? With all of them pulled out I would probably half fill the bin, so it's a significant amount of material.
My THEORY is that in healthy soil or a fairly vigorous compost heap, "bad microbes" have to compete with "good microbes". In time their population should decrease if other conditions don't encourage them.
But if your compost heap is small and you don't let things sit there for many motnhs, maybe saving a big pile of very infected leaves is asking for more trouble. That's why many people try to rotate their disease-prone crops as much as practical.
One friend calls it "the dead relative principle". If you leave dead plants right near the same variety that aren't sick yet, diseases will spread, or at least you'll make the live ones depressed and anxious! That's why he pulls weeds and then lays them down in the same row, to intimidate related weed seedlings.
Could you spot-compost the abd leaves (bury them) somewhere they won't cause trouble? Like a flowerbed? Or make one mini-compost heap for just them, and then use that compost on the lawn far from your squash beds?
Or make a new "lasagna bed" with diseased leaves near the bottom so they don't throw a lot of spores around, but you still get their nitrogen and organic matterf.
But if you want to not worry about it (I mostly don't) , here's some rationalization.
Some fungus or virus or bacterium specialized for infecting leaf surfaces might be at a disadvantage competing with all the soil microbes that are spoecialized for living in soil, or digesting dead matter.
In a big enough heap, digesting for long enogugh, and then spread and turned under, the bad microbes would be at least diluted, but probably not eliminated.
If you have conditions that encourage powdery mildew to spread and grow on leaves, probably nothing you do with the dead plants will HELP very much, and re-using them will only make a bad situation slightly worse.
If your growing conditions are ieal for combating mildew, maybe re-using diseased leaves would only make the problem go from negligible to slight.
No matter what you do with the dead plants, try saving some seeds from any plants that look helathy while everyone around them is rotting. THOSE plants have the genes you want. And shop catalogs for mildew-resistant OP varieties, and save those seeds. If they grow healthy even in spore-rich soil, they are winners!