It takes several seasons to achieve notable results. For zucchini, instead of row covers or shaving cream, I prefer succession planting. I pull the plant out at the first sign of the borers, destroy the worms. There is no loss, since more plants are maturing, and zucchini is so prolific. For flea beetles, I cover the sides of the eggplant cages with a light row cover so they cannot get to the plants.
Radishes are harvested so quickly, there is no appreciable damage.
And, I no longer grow mustard or turnip greens in favor of swiss chard which is not on the beetles' menu. In zone 5, mustard and turnip greens can be grown in the fall, after the flea beetles are gone. For corn borers and other corn lovers, my solution is an easy one. Corn is a grass and can stand light frosts without damage, but will not sprout in cold soil. As a result, all my corn has been harvested between July 12th and July 18th, before the attackers of corn become active.