Cauliflower With Black Spots on the Stems

Grow cauliflower at its preferred temperatures to avoid many cauliflower diseases.

Cauliflower is a cool-season cole crop that is grown for its thick, white flower heads. Cauliflower thrives in temperatures ranging between 60 and 70 degrees Fahrenheit, but can withstand light frosts also. Growing cauliflower in warm temperatures often causes many cauliflower diseases to form, especially when mixed with abundant rainfall or improper irrigation methods. Many cauliflower diseases persist in the soil for several seasons, making crop rotation essential.

Black Leg

Cauliflower plants that form a sunken lesion at the stem's base indicate the first symptom of black leg. The lesion overtakes the entire stem and forms black dots, which are fungal structures. Rain and irrigation encourage spreading of the fungal spores. Serious infections cause the plant to fall over because the stem becomes so weakened. The disease persists in the soil and on garden debris for at least three seasons. Remove badly infected plants and remove plant parts on those that are only mildly affected. Remove and destroy all garden debris, including mulch. Apply a Bordeaux mix, a fungicide made with copper sulfate and hydrated lime.

Wirestem

Wirestem causes the cauliflower's stem to form black areas above and below the soil, which eventually encompasses the entire stem. The stem becomes leathery and shriveled, which causes young cauliflower plants to fall over. Mature plants remain erect, and if severely affected, die. If they do continue to grow new roots, the cauliflower plant produces small, irregular-shaped flower heads. Remove and destroy all infected plants. Spray the remaining cauliflower plants with a copper fungicide.

Black Rot

Black rot, a disease caused by the bacterium Xanthomonas campestris pv. campestris, spreads rapidly when conditions are warm and moist. Black rot disease spreads quickly and devastates entire cauliflower crops if not controlled. Because the bacterium subsists in the soil for several years, use precautionary control methods for at least three or four consecutive growing seasons. Black rot affects cauliflower plants at any stage and is identified by the black spots on the stem and brown flecks on the leaves. Remove and destroy all cauliflower plants that are badly infected and remove the infected plant parts of those only mildly infected. Remove existing mulch and cover with a fresh layer. Use a copper-based fungicide to prevent the disease from spreading.

Downy Mildew

Wet conditions during the early part of the fall season tend to breed downy mildew. Several symptoms arise with downy mildew including brown to black spots on the stem that eventually become darker. The leaves also form angular yellow spots that turn brown in the center, and the undersides of the leaves accumulate a gray fluffy growth. Spores are carried on air currents and spread by splashing water. Remove infected plants and improve drainage and air circulation to promote drying. Use potassium bicarbonate to prevent further spread of the disease.

References

• "The Organic Gardner's Handbook of Natural Pest and Disease Control"; Fern Marshall, et. al; 2009
• "Ortho's Home Gardener's Problem Solver"; Michael D. Smith; 2001
• "Natural Insect and Disease Control"; Roger B. Yepson; 1984
• "The Gardener's Guide to Plant Diseases"; Barbra Pleasant; 1995
• "Vegetable Gardening"; Fern Marshall Bradley, et al.; 2006