Lots of tiny holes in leaves are a sign of flea beetles. It looks like someone shot the leaf with a shotgun loaded with birdshot. These insects can destroy small young plants rapidly. Flea beetle larvae also weaken plants by feeding on the roots.
Flea beetles can be a problem in the flower bed or even on some shrubs and bushes. However the most common target are some of the vegetables in the veggie garden. Eggplants, peppers, and the cole crops (broccoli, cabbage, etc.) are the most commonly hit.
How Many Make a Problem?
Generally, if you see any small shot holes developing on a new seedling or young plant you need to act immediately. More mature plants can handle a few shot holes with no long term effect. However, any plant with lots of leaves with shot holes is vulnerable and the beetles need to be attended to.