http://www.territorial-seed.com/testcat/culture/rdh_cu.html RADISH INSECTS: More than slight flea beetle damage (pinholes in leaves) can reduce growth rate and thus reduce quality of the radishes. Control heavy infestations by frequent spraying with a Rotenone/Pyrethrin spray or using an insect barrier or row cover such as Reemay or AG-19. Root maggot populations can also be reduced by using a row cover. You can reduce the amount of time (and therefore the damage) that root maggots have to invade the radish root by encouraging rapid growth, followed by prompt harvesting.