Caterpillars probably you need to pick the little blighters off and squash them.

If the holes are very small then it's more likely to be flea beetles. You can get a chemical spray to control them, but the name escapes me for the moment! (Damned senior moments!) :o)

You can also get an organic garlic concentrate which you add to water and spray on this should keep the flea beetle down. Or sacrifice a plant or two the beetles need to live too. As to the chemicals we don't use them.

thanks Moon & Nariz