Are you using the same soil or container mix each year? Some diseases are soil-borne. Also, containers are famous for difficulty watering - very sensitive to too much or not enough.

There is clear damage to the stem in the pic and there are SVB eggs (small black dots) on at least two of the stems I can see. Look up squash vine borers - lots of info here on them.

Dave

Thanks! So, does that damage look typical of a SVB? Or do I have two problems?

(And I did try a different container this year in case it was a problem with the soil in one container, but that does not seem to have helped).

Although, I just went back outside to inspect and I think the dots may just be dirt. They don't look like the photos I have seen of the eggs and they brushed right off. I agree that there is damage, though. I am just having trouble finding photos of damage that match mine.

And it may be completely unrelated, but my nearby pole beans have been doing this for quite some time now (although they have been producing fine). This had me thinking it was a fungus or a deficiency until I spotted the stem damage on the zucchini because the leaf damage looks similar.

Slice the stem open near the damage to check for SVB.
Could the beans beans be too much or too little water?

<So, does that damage look typical of a SVB? Or do I have two problems?>

Typical? No, but clearly something has been chewing on it and the plant itself does have the typical SVB appearance. The beans look like they have been fed something with nitrogen in it - burned and curled leaf edges. Beans like all legumes don't tolerate excess nitrogen at all well. They can't be grown well with other crops that do require nitrogen supplements.

Dave

Do you have squash bugs? Flood the plant and see if any come out. If you do it is a big problem, hand picking the bugs and smashing the eggs is about all you can do.

I'm leaping in without reading any replies as the dog is waiting for me.

At a quick,first glance, the soil in your pot appears to be potting mix. This will dry out extremely quickly. Once the plant is weak from lack of moisture (if this is what happened) then perhaps it will be more susceptible to attack from other things. I know this is true of Eucalytus for example. And yes, Eucalytus is a tree and Zucchini isn't, no matter what the ambitions of a zucchini might be, but maybe any weakened plant will attract insects with evil intentions.

Hmm... have you been using the same potting mix over and over?

I feel that your problems stem from this, not bugs and insects. I think you need to get some really nice mix and start again. Your plants are possibly saying that they aren't happy with their growing conditions.

Well, the appearance of SVB damage is pretty obvious. Look for damaged and penetrated stems (as if they are sliced open with a knife, and getting brown in the sliced-open area) down below the wilting leaves. Not on them. That's where the SVB would have bored into the stem and is making mischief there. For example, in your second picture, you'd see that damage just above the soil line on the main stem as the whole plant seems to be affected. If the main stem there isn't damaged, but just looks like it is dying, the problem isn't SVBs. SVBs are not, by the way, nation wide, but they are endemic in New York.

Thanks everyone! It's supposed to be a veggie mix for container gardening and I did mix in some new material this year, but I will do a soil test next year. My gardening skills are rather rudimentary, but I am trying to learn. And it was actually really rainy for a while, so I was thinking I had the opposite problem, maybe some sort of anthracnose. (I've just noticed odd brown spots on my nearby currant and blueberry bushes as well, so I'm really hoping it's not anthracnose.)

I gave the zucchini a little food and used some chamomile from the garden to make a calcium spray and it seems much happier now. The leaves are still in bad shape, but I will keep all these helpful suggestions in mind as I continue to monitor it for signs of what has gone wrong.

the 2nd photo looks like the dirt is old with lots of old roots in it from a previous year. Dirt can have soil borne pathogens and diseases in it as mentioned. Especially concetrated in a pot. Even house plants after a year or 2 will do better repotted in new potting soil. In this situation though at least the second photo looks like it froze or is dried out from either lack of water or some sort of pest like a vine borer that prevented adequate water intake