Once Verticillium is in the soil, it's in the soil for *many* years because of its resistant resting spores.

Frankly I'm suspicious of just what the problem is. More often than not in a home garden, the problem is cultural and/or environmental and/or insect/critter damage.

How was the Verticillium diagnosed? And by whom?

I diagnosed the verticillium visually. It has deteriorated a lot since yesterday. The edges of the leaves are wilting quite fast, first becoming light brown, then drying and withering to a pale beige. The dried edges readily break away to the touch. It all started by the edges of the leaves and it seems to move steadily toward the center of the leaves now.

It is right next to another squash from the same pack and their leaves are sort of intertwined. The difference is striking. The sick one has smaller leaves that are not quite as green as those on the healthy one. Bluntly put, one is magnificent and the other looks like it's dying. I don't like having to take it out because the two of them support each other by providing male blooms to each other, but leaving it there will only, if anything, make other plants sick.

Let me see if I can get a picture...

Yes, please try to post a picture or two.

Include several views if possible. One overall, another midway, one of the lower stem and whatever else you think may be important.

Yes, without a picture, I doubt the problem is verticillium wilt and suspect SVB instead.

What variety is your squash?

Thanks for all the replies. I am glad there are people out there trying to help.

Pictures are coming! It's just that my cat hid the camera cable and he has died since, so I can't ask him to give it back now. The card is not compatible with my PC, but I will ask DH to upload pictures.

In the mean time, I am sorry to say I have no idea what kind of zucchini they are. I bought started plants at a nursery as I was swamped this spring and didn't have time to sow seed like I usually do. The label simply said green zucchini squash. I just harvested one from the healthy plant and it looks like your run-of-the-mill supermarket kind.

Both are blooming fine, alternating between male and female flowers. The sick one has three pollinated squash growing on it and three male flowers about to open, which is just nice, because the healthy one has three females about to bloom. I am thinking I will wait to hand pollinate before taking the sickly plant down.

Stay tuned for pictures!

Thanks again!

P.S.: I planted my raised bed quite tight so a lot of stuff is growing nearby. Other than the usual critters, no sign of disease anywhere except that one squash. Should verticillium quickly take over the entire bed? If that is the case, then I too am starting to have doubts...

Let me repeat -- we suggest it's NOT verticillium.

Alright, here are the pictures. Sorry if anything is missing from them. I took these in the afternoon and now, it is night, so new pictures would be pointless at the moment.

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Healthy squash to the left, sickly squash to the right (the yellow bit peeking through the stems is a tiny squash rotting away)

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A closer look--note that the large green leaf is one of the largest on the healthy plant and the small yellowing one is a medium leaf on the sickly one. The difference between leaves on healthy vs. sickly plant is not this big, and the leaves on the sickly one have shrunken quite a bit today (getting dehydrated I guess).

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Closeup of severely affected leaf

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Detail of the same leaf

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Another leaf, less severely affected

Also, since I took these pictures, the leaves have visibly deteriorated some more. The edges are beginning to curl up on the larger ones. I am afraid this plant is dying a horrible death. Can I help it?

Alright, I checked what SVB looks like and then I put my headlamp on to go and inspect the plant. The stem looks normal. It is dark green, shiny and there are no holes. Otherwise, from what I have gathered quickly, the symptoms look about right. It does kind of look like my plant somehow doesn't have access to water.

I will examine the stem again in the morning, but in the mean time, do you think SVB can be outruled? Let's say it isn't SVB and it isn't verticillium. What else could this be? I have a feeling whatever it is, I will have to act quickly to cure it or at least to protect nearby plants from it...

I still don't think it's Verticillium, an exceedingly rare disease that would affect your other zucchini plant since it's soil-borne. IOW, both plants would have the same symptoms from the get-go.

It appears you are doing Square Foot Gardening, since I see a grid of sorts. Are your zucchini plants not planted too close to each other? My one zucchini plant is now nearly ten feet in diameter and has completely covered a bell pepper plant that I set out four feet from it!

Below is a link to an excellent cucurbit plant disease site.

You can explore various diseases and insect damage by clicking on the area you are most concerned about under Cucurbit Disorders.

Here is a link that might be useful: Cucurbit problem solver

I'd suspect downy mildew, a common but serious disease, given the yellow spots on the leaves.

If that's the problem, you'll do well to spray the plants regularly with a fungicide.

Thanks for the link to the cucurbit disease page, anney! I searched through it and the closest match seems to be molybdenum deficiency!

The reason why I don't think there is any kind of mildew problem is because there is no substance per se on any part of the plant and because the colours don't match with any mildew. Also, the symptoms systematically start with the edges of the leaves. Mildew doesn't really work like that.

To me, this looks like some kind of virus or something feeding on the plant. I have no idea why this plant would have a deficiency while the other clearly doesn't. They are in the same soil and they get the same care. Same thing with bugs eating them: they are so close that if a parasite were feeding on it, the other plant would have the same problem as well.

I did find a small cluster of tiny black eggs on a squash flower this morning, but they look like those of the tiny black fruitfly-like insects that live in tomato plants most of the time (there are toms nearby).

By the way, it isn't a square foot garden, just a raised bed that had to be reorganized slightly once I discovered that one of my tomatoes is going to turn into a Christmas tree. Some plants were shaded by it so I moved them. But the squash were never bothered by this (I would not dare transplanting those) and they still live in their original conditions.

One thing I noticed, though, is that there are yellow ladybugs visiting this plant. I only ever find one and only once in a while, but whenever I find one, it is on one of the squashes--I crush them. Please, don't tell me I have been crushing a beneficial!

Now, I have a big question. If I were to cut off two stems with leaves, would that hurt my plant in its current state? We don't have what people call extension services here, but I do have a botanical garden 15 minutes from here by bus that offers the same services. I could have a professional take a look at plant samples. So, if I were to take samples, would the benefits (getting a diagnosis and hopefully treatment) outweigh the risks (making my plant even more sick and possibly spreading whatever afflicts it to other plants)?

Thanks so much for your help!

I transplanted the sickly squash to a half whiskey barrel to isolate it. Maybe this will help to remove the aggressor from the raised bed. In case the problem can spread, maybe I can prevent it from spreading by removing the affected plant.

The transplant looked okay but it became saggy later. I guess this is okay--most plants have reacted this way to transplanting in my experience and all have recovered. If the plant stands back up tomorrow, I will know whether it has any vitality left in it to be worth saving.

I will bring samples to the botanical garden tomorrow and will report the diagnosis. I have a friend who works there and he says whatever is afflicting my plant seems to be quite uncommon as he has never seen similar symptoms on any botanical garden cucurbit. He says the only thing that would look like this in his experience is verticillium, but he agrees that that isn't what my problem is.

I will report back when I have info.

My trip to the botanical garden wasn't much help. The people there took a few guesses but they didn't really know. They said the same thing everybody says: they don't know of any cucurbit disease or ailment that would start by affecting the leaf margins. They did suspect some kind of mushroom, and they suggested I simply destroy the plant.

Meanwhile, my other squash has the same symptoms. Looks like I am losing all my squash. I think whatever this is has got to be soil-borne or transmitted by an insect, as I bought a four-pack, half of which I gave to a neighbour, and upon seeing her two squash plants yesterday, she clearly doesn't have this problem (yet?). The funny thing is she has old, poor soil and mine is new, healthy and balanced (I made my own mix).

So far, even the plant that got sick first keeps growing new leaves, although this occurs slower than in a healthy plant. The new leaves look healthy. I have just tried an experiment: to cut off the sick leaves, leaving only the healthy ones. Somehow, I suspect that whatever the problem is, it spreads to the rest of the plant and if I cut the affected bit off, the plant may just survive, and maybe even get rid of whatever ails it. I know, it sounds quite useless and silly, but I want to get to the bottom of this.

Stay tuned for news on the experiment.

Did you check your ph? Added something slow acting that is just now starting to affect it? This happened during the flowering stages, so maybe a lack of something. People have been complaining about miracle grow products, so maybe the soil was bad?

The I searched and found an iron deficiency would cause this kind of behavior leaving your leaves with dark green veins darker than your plant. This looks to be like what you have.

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What would cause iron deficiency in a good soil? High ph is one of them. I'm not sure this helps, but maybe. The link below expains why it might happen. It could be your water. Is it unusually high in chemicals due to drought conditions? Are you under water restrictions? Your plants look well watered. Do you water in the evening? It's best not to water during midday sun or in the morning unless you have a lot of rains. In hot weather it's preferred to water at night, so the midday sun can't steam your plants up with evaporated water and burn your roots with the heat.

Here is a link that might be useful: Low Iron in Soil

I'm thinking your "yellow ladybugs" are cucumber bugs. I have both striped and spotted (saw spotted for the first time yesterday) but I've been keeping their numbers low (fingers crossed) with neem oil spray.

They transmit bacterial wilt, which may be what's going on with your plants. I was given this link when I was questioning what the pests were on my pumpkins, and I've seen a few now on my cucumber and zucchini blossoms. When I see them, I spray them with insecticidal soap (being sure to shoo away the bees first) and then apply neem oil, which I don't think kills them right off, but keeps them from "feeding".

See if this seems accurate.

-veronica

Here is a link that might be useful: Cucumber Beetle/Bug

Aphids they ruined my squash plants every year! look under the leaves they leave tiny black eggs all over the bottom of the leaves. They're extremely hard to stop.