Zucchini Yellow Mosaic Virus (ZYMV). Only cure is to use a resistant variety. Fruits are edible.

Interesting. Thanks farmerdill. That's a bummer.

How did you identify it? I just looked through traditional symptoms if ZYMV and my plant doesn't meet any of those. The foliage doesn't exhibit the mosaic, the growth isn't stunted, and the green Zucchini it produces appear perfectly normal to me. I'm not sure how the plant would have contracted it either. It's been growing for well over 2 1/2 months now and these are the first yellow Zucchini it's producing and I'm in a suburban area, there isn't commercial agriculture within 50 miles of me. Haven't seen an aphid yet. Been looking for them!

Do you have a favorite ZYMV resistant variety that you like to grow?

I cant't see enough of your plant to verify. Basicly I am judgeing by the fact that yellow squash on a green fruited plant is caused by a mosaic virus. Cucumber mosaic (CMV) which I am most familiar with turns yellow squash green, ZYMV puts yellow in green squash. I don't ZYMV yet, so I can't say for sure. I grow mostly middle eastern type zukes as I prefer the flavor and texture.
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Here is a link that might be useful: squash diseases

farmerdill,

I think I may well give those a go next year! They look delicious and I've become a bit of a squash addict it seems.

I just added a full-view photo of the plant -- my apologies for the apparent dirtiness of the plant, the tree above it sheds at a ridiculous rate. Aside from some leaves with powdery mildew (my own fault for watering from above, duh) and some dried milk marks from attempting to get rid of the powdery mildew (didn't work), I don't see much else wrong with the foliage. No mosaics or mottling what-so-ever. I have been reading a bit since you suggested ZYMV, and it seems that some seeds can be tolerant to severe strains of ZYMV and only show weak symptoms of infection. Perhaps that's it.

In any event, a green female blossomed today, and 2 more will tomorrow, and a yellow female is close to blossoming. I intend on growing all of them out to see if any of them are misshapen and what color they ultimately take. The four that I've harvested thus far were all nicely-shaped and green. I'm still not *totally* convinced it's pathogenic, but the next couple weeks should be telling.

Can you notice anything in the foliage that might be suggestive?

Not virus.

Are you considering the white veining as Powdery mildew? If so, stop treating it as that's normal silvering.

Thanks Jean.

Is this the silvering induced by silver-leaf whiteflies? That seems feasible to me.. I remember several months ago seeing tiny white flies around the Zucchini. I'm also noticing the leaves of my bush beans and tomato plant getting many, many tiny holes in them, as if something's been eating them.

Have you had any success in treating this?

The silver veining is a common feature of zucchini, some varieties show more than others. It is genetic not caused by any disease or insects.

Okay. Great. :) Would this somehow explain the yellow fruit?

Thanks for the info Trev. I hadn't considered that but it's looking like you're right! All the yellow ones have died and only greens remain. A few weeks ago I think I slightly over pruned and since then I've fertilized and there's much more foliage and I'm seeing fewer yellows females emerging. In fact, right now that single plant is growing 4 hefty Zucchini with 2 more females blossoming tomorrow! Yay! As an aside though, should I be allowing all 6 to grow or will that impact the health of the plant and the quality of the fruit?

Great information Trev. Thank you!