Holes in the leaves seldom bother them, Its the sucking pests like squash bugs, cucumber beetles, and squash vine borer that usually take the plant down. I would suspect bacterial wilt on the cucumbers, spread by cucumber beetles. If the older leaves are dying and you still have green growth, Powdery mildew is a possibility as it it affects both squash and cukes. Other cuke problems that sometimes arrives is Anthracnose and angular leaf spot. If it is powdery mildew ( white powdery substance on the affected leaves) you may be able to salvage your plants if they have not lost over half their leaves and you are able to halt its progress with a good fungicide. Baking soda works about as well as anything, Just put a small box of baking soda in a 10 qt sprinkler can and cover all the leaves.

No matter what you do or don't do, PM is something that shows up each and every year on your squash and cucumber plants in late summer. Its pretty much just a fact of gardening. Treat or don't treat, depends on if you've had your fill of zukes yet or not (by September I most definitely have lol). I usually just let it go at this point in the year. Course here we can expect snow in 2 weeks anyways and that will kill off any squash plants regardless.

Hi Gardenerenthusiast, I am glad you asked this question because the same thing has been happening to me, on both my zucchinis and my spaghetti squashes. Along with rotting blossoms that don't open, I've been getting female blossoms where the squash has shrivelled up before the flower even opens. My plants are otherwise healthy, though I have just started to see some yellowing on the leaves. Unfortunately I have no idea what is causing this, though I've narrowed it down to blossom end rot (which would mean a lack of calcium in the soil) or under watering (it's been very dry here and I've been watering shallowly and regularly, instead of deeply), or some kind of virus/fungus etc. I can't see any trace of pests on my plants, save for a few black aphids, and there are no signs of squash vine borers. One of the strange things is that it suddenly affected my zucchini, spaghetti squashes, and now my delicata squashes all around the same time, even though they are in different garden beds. This makes me think it is either the weather or a virus. My current theory is that I haven't watered them deeply enough, and also that they might need more plant food since they are quite close together and fruiting heavily. Sorry I don't have an answer for you, but I would be curious to know if any of that sounds familiar to you. Good luck!

I had this problem all the time. I could never find an answer either. It certainly didn't seem a lack of pollination. I'd get those early abortions, where the female flower didn't even get to bloom before yellowing and dropping off. I'd also get the ones that yellowed and dropped off after pollination. And I know for fact they were pollenated because I even took the anthers of a male flower (and sometimes even from a different plant of the same species), broke them off and forced (aka raped) the flower by placing a fully pollen loaded anther on the stigmas. I even tried this in the morning. But still....a good number of them aborted. Without any references to turn to, I came to some very likely theories (which I believe very possible anyway) 1. The plant isn't big enough. I may think it is, but the plant may not be ready. 2. Not enough total male flowers have opened in the plant's lifespan? (like the plant keeps count???) 3. Not enough light??? I had significantly more squash abortions in a part shade/part sun spot in my grandma's yard than the last year when I planted in a sunnier spot. - Even still I had a great number of abortions earlier in the season until the vine got gigantic. (point #1 may be in effect) 5. Plant's own health? I noticed later in the year as the squash vine borers took ahold of the plant, there were a lot more abortions. Especially true with zucchini. The plant might look healthy, but if that one branch had a larva feeding inside it, then the first sign of death would be a lack of blooming female flowers and even more rare ones that produced squash. 6. The weather. More specifically night time temps. It may be the night time low temps have to be under a certain temp. I noticed no matter how early I planted or how large a vine I got to grow indoors before planting,there was always a dearth of mature squash (specially winter varieties) in mid July. This would be true even with the one spring in 2011 when I got a squash growing in June. It almost never failed. As long as the lows didn't drop into the lower 70's for summer squash or 60's for winter types, I could forget having any new female flowers for that week. I'm guessing lows of 80's kills the pollen or the flowers??? Idk. But as soon as the low temps cooled down in the 70 or 60 range, then I'd get a successful pollenated and developing squash. Right now I believe out of those points #1 and #6 are the most likely. I just wish I could find more scientific evidence to back up my theory.