It looks like downy mildew and you may have some mites or aphids. Check under the leaves, they are common this time of the year. Cucumbers need good drainage but a lot of water especially in the heat of summer. It is also better to train the plant up the fence and not let it sprawl on the ground especially if you want straight fruit. In the open you may have to cover the fruit with stockings or newspaper to keep out the caterpillars in June.
https://www.cals.ncsu.edu/plantpath/exte ... Mildew.htm
https://www.clemson.edu/extension/hgic/p ... c2207.html
P.S. Aphids come in all kinds of colors, the ones that go after my cucumbers are black/brown. Mites have webbing under the leaves and if you tap the leaf over a piece of white paper and you see tiny specks that start to crawl around after about 30 seconds to a minute, then it is probably some species of mite. Mites and aphids suck the life out of the leaves causing them to wilt, turn black from sooty mold, the edges of the leaves will brown, stippling on the leaf, and if it is severe enough the plants will be stunted and the tips will start to die. Fruit will be small, curled, and frequently will prematurely yellow and fall off.
Happy gardening in Hawaii. Gardens are where people grow.