French marigolds planted among carrots will attract hover flies which in turn will feed on the carrot fly.
Maybe not a form of pest control but "companion planting" which was highly successful combo of squash, beans and corn (maize), known as the 'Three sisters', the Mohawk and Iroquois tribes have been planting these crops together for thosands of years. The squash would grow happily under the shade of the corn and keep it's roots cool and keep the weeds down, while the beans would climb the stems of the corn for support and as an added bonus, the beans would fix nitrogen in the soil with their root nodjules, thus providing nutrients for the corn and sqaush.