Foilage and Leave Problems
Holes from insect feeding
No treatment normally required.
Yellow or brown areas accompanied by white mold
Downy Mildew (Peronospora parasitica), a fungal disease that develops during cool most conditions.
Avoid shaded plantings
Purple or black root
Black Root (Aphanomyces raphani), a fungal disease which causes the radish skin to turn purple or black in a single area. As the infection progresses, the entire root may be girdled.
Avoid warm weather plantings, and storage conditions.