Never seen that before. What caused it? Fertilizer? Herbicide? What ever liquid hit it, caused it... You can try and let it recover.. It's a good sized plant...

Wow that looks horrible. I agree that something toxic to the plant got on it (weed killer, etc)

I think it's mostly that you moved a very mature plant. Any root disturbance after a cucurbit starts blooming leads to the dark side.

Agree with planatus. Transplanting such a large plant is problematic at best. You likely lost half of its root system and a larger percentage of it's water-absorbing feeder roots. The leaf canopy will suffer in kind.

Do you mean" it is in a pot" and you moved it from your front porch to your front walkway? Or do you mean you transplanted it? It looks like it is in a pot. Did it go from a shady location to sunny one?

Look at the bottom right of the picture.. It looks like a liquid hit it or there was something on the leaves that mixed with water and it damaged the leaf... Squash plants that I've seen that were severely damaged during a transplant would have droopy leaves the next day and the leaves would die over the course of three days...

Thanks for all the great responses, and I'm sorry I wasn't terribly clear in my description last night! I'll try to answer your questions now.

This plant is indeed in a pot and I just moved the pot from the porch to the walkway. My porch is pretty sunny, but I do have some pretty tall tomato plants that may have been providing some shade to the squash plant. So the plant may be getting more sun in the new location than in the previous one. Also, I don't think there was anything mixed in with the water that hit the plant. The water that hit it was from a sprinkler as well as from a thunderstorm we had Thursday night. The plant is pretty close to my lawn now, but I haven't fertilized recently. And I don't do any weed treatments because I'm a bit of a hippy.

Do you all think that just getting too much sun all of a sudden could do this? Or too much water on the foliage? I've been careful not to spray the leaves when watering up until now, so maybe that allowed disease to incubate?

If it's the sun problem, I'll happily move the plant back to the porch. If it's a disease I don't want to bring it back up just to infect all my other plants!

The young leaves look ok. Some look damaged from the move. Usually if too much sun, the leaves will droop. You're sure nobody poured anything on it when you weren't looking? (Long story when had aquarium fish. Lol) Was the sprinkler attached to a hose and turned on during the heat of the day..? I know the hot water in the hose can cook plants when initially turned on. Yea, you generally don't want to get water on squash leaves to prevent powdery mildew. I think the plant will be ok though...

I'll give it a few more days to see how things go. The sprinkler is an in-ground system that is set to water in the early morning, but I'll check the timer in the morning; I think it's gotten off if we've had a power outage before. Wouldn't it be great to find out it was an easy fix?

Oh, and I really hope I don't have anyone around me who would poison my plants behind my back! My neighbors are pretty friendly and I'd like to think they'd let me know if they had a problem with me.

I have considered the possibility that one of them got their yards sprayed with a weed killer and this plant caught some overspray. I should go see how my clover is doing . . .

The reason I asked about the difference between the availability of sun to your plant from when it was on the porch verses when you moved it to the walkway is because I have done that before. I have found that, especially with big leaf plants, indoor as well as outdoor big leaf plants, if I change the amount of sun that they receive the leaves will quickly turn black and roll up. My "guess" is, if you will move the plant back to the more shaded area (what it is used to), as soon as possible, it will recover slowly without much intervention needed. Maybe, once you have a lot of new growth you can clip off those damaged leaves once they fully die. Well, that has been my experience anyway...

I also wonder about the move into more sun as the problem. If you have experience of starting seed indoors, you understand that you have to gradually acclimate your new plants to more sun exposure before planting out. Maybe this is the same idea. Moving a potted plant from shade to sun should be done carefully. Maybe covering the plant or shading with a lawn chair until it gets used to the new location. Moving in a time period of 3-4 days of rainy cloudy weather. Etc. No experience with this issue though, just a guess.

Thanks, guys. I was thinking at the time that I did it that this was a move from full sun to full sun but I do think that it was probably getting afternoon shade from the tomatoes in the old location. So partial shade to full sun.

Now to find someone who will help me carry it back up the stairs!