There are different kinds of fungi that can kill your radish or make it taste really bad. Usually there are obvious signs of a fungus problem that you can watch out for and subsequently deal with. Crop rotation, removal of infected radishes, clearing up nearby plant debris and making sure your bed is well drained helps with most fungal problems. If your leaves are looking faded and you find that there are tunnels and grooves in the roots, you might have root maggots. These tiny critters are small, gray/white, legless worms. Flies lay their eggs in the soil beside the plant. To get rid of them, add lime or wood ashes to the base of your radish plants. Wait to plant your radishes until the weather is drier so that you avoid the maggot’s life cycle. If you have tiny holes appearing in the radish leaves, you might have flea beetles. These little critters are bronze or black beetles 1/16th of an inch long. If you find you have these, spread diatomaceous earth, a type of soft, sedimentary rock that crumbles easily into a fine, off-white powder. This can act as a natural bug killer. You should also cultivate the ground often, so that you disrupt the beetles’ life cycle. If your radish plants have whitish or yellowish spots, have deformed leaves, or if the plants are wilting, you might have Harlequin bugs. These bugs, which are black with yellow or red or orange markings, suck the fluids out of the radish’s plant tissue. Pick out and destroy all the bugs and the egg masses. To help keep them out of your garden, keep it clear of the places where bugs breed, like crop residue and weeds. If the leaves of your radish plant turn a dull yellow, if they curl and become brittle, your radish plant might have contracted Aster yellows, a mycoplasma disease spread by Leafhoppers. If this is the case, remove the infected plant or plants, and control the leaf-hopper population by keeping down the weeds and plant debris.