Is it a container variety of plant? And how big a pot? Unlike winter squashes, summer squash don't vine, but grow a large bush. I'm sorry, I have no answers to your questions, but the further info may help someone else who knows.

Whether it is a vine or not all depends on the variety. There are easily 50 varieties of zucchini.

From the photo I would suspect it is just a break from the branch weight and that is a fairly common problem when even the bush types are grown in a container, especially when the container is to small to "contain" the plant. As the plant outgrows the sides of the container the weight of the branches causes bends and breaks.

However SVB (squash vine borers) are also a real threat. That yellow in the pic could be the dross of an SVB and I see all sorts of little black specks on the stems that are possibly eggs. But they don't normally cause a full break like that. No idea what your zone or location is but if you have a plant that big already then I assume you are in deep south and SVBs would already be active there so researching them would be beneficial. Tons of info available here about them in past discussions.

Dave

Sorry for the delayed response here. (Busy work week) Thank you both for your comments.

@balloonflower, I don't know enough about the variety to know if it's specifically intended for containers, but this isn't really growing in a "pot". It's a 4 ft x 8 ft planter intended to be used as a square foot garden. The Zucchini is planted in one corner so that it's leaves will be outside of the container on 2 of 4 sides.

@digdirt2, I'll look into SVB a little more. From what I've read after reading your post, I don't think that's the case in this instance. I havent seen any of the adult moths around and the "specks" in the photo are just soil debris from rain. That said I'll look into placing some yellow traps out to keep an eye out for them. I'm hoping it's just a weight issue. I've tried gently "lifting" the branch to see if I could just support it a bit, but it seems reluctant to bend upward. I suppose possibly it could have already begun to heal in it's new position. None of the scars / wounds are outside of the container though, the main stem hasn't yet reached over the edge.

I'll keep monitoring it. I'm in Zone 9 so it's already quite large and flowering. Hopefully nothing causes it to fail completely on me. Because of the space needed I only planted one.

Thanks again for the comments!