Fat green caterpillars

For the first time, we’ve been inundated with fat green caterpillars this summer/autumn. I suspect it’s because we’ve had a very dry, warm season but the little blighters are having a great time demolishing my rocket, mint & anything else they take a fancy to! Removing the big ones by hand is very time consuming but the baby ones prove very hard to spot, is there anything you can suggest that I could spray/sprinkle around the garden that is not too expensive & doesn’t have a withholding period?