I'd check the plant, especially the undersides of the leaves, for aphids. Usually if you see ants on grapevines this early in the season they are following the aphids. They like to feed on the bodily secretions from the ants, and those bodily secretions are called honeydew. Ants like honeydew so much they will farm the ants in order to get the honeydew.

Ants alone are not harmful to grapevines as far as I know, but their presence usually signals something else is present--like aphids. If you find aphids, you can hose them off with a sharp stream of water or treat the plant with insecticidal soap. Ants in general, except perhaps for fire ants and carpenter ants, are beneficial in a garden as they haul off tons of dead insect carcasses.

I am having the same problem. Spraying hasn't worked to get rid of the aphids though. Is there a spray you recommend? Thank you!

Normally spraying with a high-pressure stream of water knocks the aphids off the plants. You may have to do it several days in a row. I don't use broad-spectrum pesticides so wouldn't know what is labeled for aphids, though I presume many such products can be found on store shelves. You'll just have to read the label of a product like Bug B Gone or whatever to see if it is labeled for use on aphids on whichever plants you want to spray it on, and be sure to read about how many days you have to leave in between spraying and harvesting. Since I avoid the use of those types of products, I cannot really recommend one to use. If you have lady bugs, they'll usually control the aphids, though it takes them a while. Spinosad is a good organic bug spray, but I've never used it for aphids so cannot say if it is effective on them. Neem oil is another organic broad-spectrum pesticide, but can damage plants if applied in high heat so it is risky to use it in summer temperatures.

To get rid of aphids or grape bugs wash of the bugs by spraying with water, then spray NEEM OIL on the undersides of the leaves and wherever else there are bugs. I get black aphids on new leaves on my Evans cherry trees which causes the new leaves to suffer and curl up, and I get small white flying grape bugs on my grapevines that cause brown spots on the leaves. Washing them off helps a lot especially with the aphids, and neem oil helps deter insects more long term. I don’t know if it deters bees, so I might avoid using neem oil during flowering.