Cabbage, cauliflower, brussels sprouts, broccoli, kale, kohlrabi, and turnip are commonly referred to as cole crops. They are susceptible to a number of serious diseases that must be controlled for quality and good yields. The diseases and control measures discussed affect the home gardener. Diseases may be caused by viruses, bacteria, and fungi.

Successfully avoiding disease problems in broccoli and cauliflower requires careful attention to good management practices. The following production practices will reduce the risk of disease in your garden:

• Practice a three-year crop rotation schedule with cole crops.

• Avoid irrigation runoff from infected plants. Avoid overwatering.

• Control weeds and insects.

• Work in gardens only when plants are dry.

• Plant only disease-free seed.

• Inspect transplants before planting.

• Disinfect equipment used in the garden if disease is present.

• Dispose all leave and debris at the end of the season.

Some resistant varieties are available.

Some of the more serious disease problems in cole crops:

Black rot (Xanthomonas campestris)

Black rot, which is distributed worldwide, is the most serious disease affecting broccoli and cauliflower. This bacterial pathogen can infect all crucifers including crops and related weeds. Disease symptoms appear first on the edges of the leaves. The bacteria enter through leaf pores and wounds, eventually producing a yellow V-shaped area on the margin of the leaf. The leaf veins within the infected areas turns black, and the leaf tissue becomes dry, brown and brittle. The bacteria then move throughout the plant. Eventually plants become stunted, wilt and die. High temperatures and humid conditions speed the disease process.

Black rot is transmitted by infected seed. The pathogen is spread in the garden by equipment, people, animals, and rain or irrigation. The black rot bacteria may survive from year to year on weeds or on plant residues.

Black leg (Phoma Lingam)

Cabbage and Chinese cabbage are fully susceptible to black leg, but cauliflower and broccoli are considered only moderately susceptible. This fungus is transmitted on infected seed, and occasionally through airborne spores. Once in a garden, it survives three years on crop debris and moves from plant to plant by splashing rain or irrigation. Infection starts on young seedlings as a bluish black discoloration on the stem. This lesion grows into a sunken brown lesion with a purple black border. Small black spots may be seen in the center of the lesion. These are spore producing structures and release a coil of pinkish spores in wet conditions. The stem lesion extends into the soil and may cause discoloration and death of plant roots. The lesion eventually girdles the entire stem, causing the plant to wilt.

Club root (Plasmodiophora Brassicae)

Club root is a serious disease that occurs worldwide. The infection process begins when the resting spores germinate and enter the plants through root hairs or wounds. The fungus then increases and infects other roots cells. Eventually the roots form large club-like mass that crack, dispersing the spores into the soil. The development of this disease is favored by warm temperatures and high soil moisture. The initial symptoms of club root are difficult to detect. Later symptoms include pale yellow leaves and a tendency to wilt during hot, sunny days. Young plants may be killed by the disease within a short time after infection, whereas older plants may survive but fail to produce. Club root is transmitted by infected transplants, equipment, windblown dust and irrigation. Avoid planting any cruciferous plant in the same garden. The resting spores can survive in the soil for many years, so the effect of rotation is not great. Always use plant transplants that are disease-free, and do not move equipment used in diseased fields to clean fields.