Tips for growing healthy cole crops in the garden are available in HGIC 1301, Broccoli and Cauliflower , and HGIC 1303, Cabbage and Chinese Cabbage . Several disease problems commonly affect these plants, especially when resistant varieties are not planted. Some of the more common problems are covered here, including root and stem rots of young plants, black rot, downy mildew and viruses. This disease commonly affects seeds and young transplants and is caused by the soil-borne fungus Pythium species.
Infected seeds decay in the soil.
Start seeds in commercial potting soil, not in garden soil. If disease has been severe enough in the past to warrant chemical control, metalaxyl can be used before or at the time of seeding. Use for outdoor seeding only, not for transplants. Apply all chemicals according to directions on the label. This disease is caused by the fungus Peronospora parasitica and can attack both seedlings and mature vegetable plants.