Mildew, most likely Powdery Mildew. See the white-yellowish spots on the leaves that are still green.

Dave

What about downy mildew.??????? Doesn't the yellowing on the leaves look like typical downy mildew.????

Sure it is possible, which is why I said "most likely". But even with blowing the pics up I can't distinguish the color differences enough to say it is for sure downey. There isn't enough contrast in the photos and what spots I can see appears more white than gold/yellow. The solid yellow leaves are just from over-watering. It is the spotted leaves and the gray dried leaves that are relevant.

And PM is much more common. But either way the treatment and end result of both is the same. In the long run it I don't think it makes that much difference which form of mildew it is since it is already so well advanced.

Dave

So they are goners?

Here are close up pictures of what is happening to the leaves.; it seems to be progressing its way from the bottom to the top of the cuces and is spreading in the squash, too.

Any help would be appreciated as this is my first year. I live in Ontario and we cannot get, nor would i like to use pesticides. Is there anything I can do the stop this?

I think the watering is the most effective. I don't think the milk etc does much of anything, IMHO.

PM is extremely common and difficult to prevent and control. If you have had major problems with it, try a variety that has some resistance (though they still get PM.) My alexandria zucchini has almost zero PM while all my other cucurbits are struggling badly, and I recommend it.

Also last year I had zucchini that were pretty much gone from PM come back with new healthy growth in the Fall. If you don't want to plant something else, I suggest not pulling plants.

Though I have no idea what that picture is above.... it doesn't look like PM, but dk.

What is dk?

Sorry that should say idk not dk... typo.

Thanks...but what is idk?

Idk = I don't know

Lol - too funny.

That looks more like downy mildew to me: https://en.wikipedia.org/wiki/Downy_mildew

I have powdery mildew. Milk with oil and dish soap has been working for me. My sugar pie pumpkins stopped producing until I started using the solution.