Clear plastic lets sunlight in, heating the soil, and doesn't let heat out. Black plastic just heats the plastic. Keep in mind that solarization will really only sterilize just the top few inches of soil. That being said, some seriously damaging cucurbit fungi are pretty heat tolerant. Chemical fungicides might be your best bet.

There was a thread on one of these forums recently where they seemed to say that clear plastic works for hotter climates, like in the south, but you need to use black plastic in the northern states. If I find the thread I’ll post a link.

Clear vs Black for killing weeds (same principle)

The other thread was about eradicating weeds rather than disease. It was the exclusion of light that made black plastic effective, not heat. I'm not convinced solarization, which, by definition, involves clear plastic would kill fungi.

The other thread https://www.gardenweb.com/discussions/6485356/is-a-black-tarp-an-effective-way-to-kill-weeds#n=11

Clear plastic solarizes. Black plastic smothers. I have used both with success in zones 5 and 6 in the midwest. Both have their pros and cons. How long it takes to kill or interrupt what's under it can depend. On what's under it, what the summer season is like while it's covered, ect. In general, most suggestions are to cap it for a whole growing season, though specific kill times might be more like a few weeks.

Something to note is that while solarization can work on some fungus issues... others are heat tolerant and can survive the process. Do you know what kind of fungus is doing the damage?

ah, I thought they were both about heat. Thanks for the clarification.

University of Minnesota advises clear plastic for real solarization. They're way up north. Hard to understand how black plastic could do much of any real solarization, as in soil heating. Keeping the sunlight away from the soil doesn't heat soil. Their web page makes it clear that black plastic is more useful for occultation, which is just to block light from weeds. So if this is about weeds, take your pick - black versus clear. Two ways to kill them. If it's about killing fungi and borers, clear is the only hope. But I suspect it's a poor way to do it. Borer coccons can be six inches deep, and solarization heating won't ever reach them. I guess if you don't turn over the soil after solarization, it might be an effective preventative for fungal infection, by killing fungal spores on the surface.

https://extension.umn.edu/planting-and-growing-guides/solarization-occultation

My experience is squash vine borers are going to find your squash. The adults are flying moths. If you killed any that wintered over in your beds, another moth will fly in and lay an egg. They lay one egg, unlike squash bugs, so they are hard to see. Some people wrap their stems (just the part closest to the ground) to prevent the borers. Others just check. You can use a skewer in the hole. There's almost aways only one grub and the stem can heal.

I have nothing against solarizing, it might work for you. However, I would suggest you figure out what the disease is, refrain from growing cucurbit for a year or 3 and then get varieties resistant to the disease. Watch out for plants just labeled "disease resistant." It might be resistant to all sorts of diseases you've never been plagued with and not resistant to the one that you suffer from.

Cucumber, Squash, Melon & Other Cucurbit Diseases | Home & Garden Information Center

Not sure what the fungus is but I do know that I have rhizoctonia solani (lab tested) in the rest of my garden which is further away from my veggie beds but could’ve very well been contaminated. Random stems of my cucumbers start wilting one by one mid season(around July) and eventually the entire plant wilts and just die prematurely, only after a few harvests. Hate to not have home grown cucumbers but I may just not grow cucurbits this year then. I’ll try solarizing it for the whole summer and see if it makes a difference for next year.

Borers are annoying but if I can’t get rid of them I could avoid it by planting kabocha seeds in July after borers are done feeding and I’ll still get some fruit by October. Tried it last year and it worked.

Solarization wouldn’t be successful during winter months. Solar energy is the key to the process. It can be very helpful for some issues but takes weeks or months of undisturbed, sealed, clear plastic application. The soil under properly installed clear plastic reaches extremely high temperatures, black plastic can’t came close. Your soil must be damp, as well.

I encourage you to purchase seed varieties that claim strong disease resistance, clean up and remove all debris at the end of the season, and don’t save seeds from diseased plants. Make sure that your seed is certified to be disease-free and don’t swap saved seeds with others.

" Random stems of my cucumbers start wilting one by one mid season(around July) and eventually the entire plant wilts and just die prematurely, only after a few harvests."

If you see spotted and/or striped cucumber beetles on your plants early on they can spread a wilt disease which sounds very simliar to your problem.

The way you describe your cucumbers dying sounds like bacterial wilt. The timeframe fits as well. It is an incurable disease spread by cucumber beetles. The adult beetles typically become active around mid June and infect the plants when they feed. County Fair is a pickling cucumber resistant to bacterial wilt. Give it a try next year and be on the lookout for beetles.

Rhizoctonia solani is a very common soil pathogen. While it can sometimes kill a mature plant it is more likely to cause damping off in seedlings. I wouldn't stress about it too much.

Rodney

Down here, I plant out squash in mid-June, when the borers are gone. My season is long enough that this works pretty well. But I've planted out earlier, and just covered until June. Pretty easy to protect small, immature plants. That way, when the plant is mature enough to flower and bear fruit in early summer, bees can help. That's a strategy to extend your growing season for squash without needing a lot of protection. .