what is is.. cuke?? squash?? melon???

and could you be a bit more specific where you are???

ken

It's butternut squash and spaghetti squash
Southern California

The first image shows something I've seen locally the past two years. Even though the leaves were that bright yellow, the plants were productive. At this time, I still don't know what it is.

Your pics:

my thoughts are iron or manganese defiency. looks like the discoloring is going from the top down and you can still see the veins which is indicating a nutrient defiency.

It does have the tell-tale signs of an iron deficiency, except for the blotchy yellow areas. That is definitely not symptomatic of an iron deficiency.

theres only three possible causes for this. low light, excessive moisture or iron and manganese defiency. im taking that there is plenty of light and the green spots are more than likely that it has not lost its pigmentation in those areas.

ive provided a link that may help you further. this is just my opinion.

Here is a link that might be useful: cucurbit leaf disorders

Thanks for the link. But nothing there matches OP's & my leaves.

Not manganese or iron deficiency. Not herbicide. Futher, mine get plenty of sun, light & water.

Anyone else with a theory?

I added some supplements, but I suppose it could be over watering (there is a leak near my garden).

Virus?

Doubt it's virus because the plants are just as productive as all green ones.

she mentioned leak, too much water keeps plants from uptaking nutrients no matter how much nutrients are added.

Yes, the plants completely white now. The green spot remained.

i had squash plants one time and they looked like tiger spots gree spots turned yellow and then white. i sprayed the leaves with a fish and seaweed emulsion. cleared it up, prob was to high ph levels. just my experience.