How often are you watering and how much are you applying? You'll want to water deeply but infrequently. This time of year once or twice a week should be adequate as long as the water is soaking down to two feet into the soil. A rule of thumb would be to apply about 6 - 8 gallons of water per vine each time you irrigate. Don't use malathion. It kills beneficials insects as well as pests and you wouldn't want to eat the fruit after applying it. Instead use a product that contains Bacillus thuringensis or "Bt", a bacteria for caterpillar control. It only kills caterpillars and is safe for humans, birds, and fish. The caterpillars are the larval form of a small, skinny black moth. When you see the adults, its time to spray. Bt is the active ingredient in Thuricide and several other products. A similar bacteria is used to control mosquitoes in bodies of water. Here is a link that might be useful: Grape Leaf Skeletonizer

'Looks like an eight-spotted forester. They make beautiful little moths If there are wild grapes in your area, moving them to those wild vines would be the best thing to do. Just cut off the leaves they're on and put them on the wild vines. I thought I had a picture of an adult moth, but I could only find this picture of a caterpillar - They have an odd method of making their pupa - they burrow into soft wood. I'm not sure you'd have that among your cultivated vines. Sherry Here is a link that might be useful: Eight-Spotted Forester

And lastly, this is actually on my Healthier vine. >> I think I wasn't watering them enough when it started warming up and only really started watering them every two days about a month ago so this could be an older leaf from that. But just putting this here in case it can help>

Okay... but some of the damage look severe. What could be causing them? Which insect? It can't be Japanese beetles because I don't see them on my grape leaves. I inspect the leaves day and night, and I can't find a bug infestation or anything that is eating it, unless if they're showing up after midnight...