| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Bacterial blight * (Xanthomonas campestris pv. incanae) |
Basal leaves turn yellow and drop. Leaf scar is blackened. Soft, water-soaked stem cankers later become dark and sunken. Plant stems may break and fall over because they are weakened by the cankers. Black discoloration of the vascular system occurs. | Seedborne and in plant debris; also in soil for 2 years. Favored by cool, wet weather. Bacteria are spread by water. | When buying seed, specify that it be grown from seed treated in hot water (122° to 131°F for 10 minutes). Follow a 3-year crop rotation. Avoid splashing water. |
| Cottony rot * (Sclerotinia sclerotiorum) |
Girdling infections that cause stems to turn chalky white. Cottony, white masses of fungus or large, black sclerotia develop on and in stems. Black sclerotia may develop in seed pods in the shape of stock seed. | As sclerotia in soil. Airborne spores produced by sclerotia only infect weak or dying tissue. Sclerotia also produce hyphae that infect plant. Favored by cool, moist conditions. | Avoid fields where disease has occurred (common disease of many vegetable crops). Apply PCNB to soil before planting. Spray foliage with thiophanate-methyl combined with mancozeb. |
| Foot rot or wire stem * (Rhizoctonia solani) |
Brown rot of stem occurs at the soil line; area later becomes a dry, sunken canker. Stems are girdled. Brown fungus strands are visible with a hand lens. Also causes damping-off of seedlings. | Soilborne fungus. Favored by warm, moderately moist soil. | Use PCNB on soil before planting. Spray iprodione or thiophanate-methyl over the row and bases of plants. |
| Fusarium wilt * (Fusarium oxysporum f. sp. mathioli) (important in seed fields) |
Lower leaf veins turn yellow, then entire leaf becomes yellow, withers, and drops. Basal leaves are affected first. Plants are stunted. Seed pods turn a light-tan color. Brown vascular discoloration occurs. | Soilborne for many years; also seedborne. A warm-weather disease; rarely a problem in the winter grown cut-flower crop. | No control necessary for the cut-flower crop grown in cool, coastal areas. Fumigate soil with a chloropicrin or a chloropicrin combination (tarped). |
| Gray mold * (Botrytis cinerea) |
A soft, brown decay that occurs on flowers or entire flower heads. Fuzzy gray fungus spores form on decayed tissues. Decay may also start on dead leaves and rot the growing points and flower buds. | In plant debris. Favored by cool, moist conditions and condensed moisture on plants. Spores (conidia) are airborne. | Protect flowers with thiophanate-methyl in combination with mancozeb or treat with iprodione. Avoid overhead irrigation. |
| Leaf spot* (Alternaria raphani) |
Round to elongate, concentric, brown spots covered with black, powdery spores. Spots are small at first, then turn gray-green with water-soaked margins. | On growing stock, cruciferous plants, and crop refuse. Favored by wet weather. Spores are airborne. Also found on other cruciferous crops. | Destroy all plant refuse by plowing under plants as soon as flowers are harvested. Spray with a copper fungicide or mancozeb during wet weather. Avoid overhead irrigation. |
| Verticillium wilt * (Verticillium dahliae) |
Foliage yellows and wilts. Leaves die and dry progressively upward from the base of the plant. Dark discoloration may occur in the vascular system. | Soilborne as microsclerotia for many years. Symptoms most severe when weather turns warm after a cool period. Host range of this form of Verticillium is different from that of the common Verticillium. | Avoid fields where disease has occurred or fumigate soil with a chloropicrin or chloropicrin combination (tarped). This combination also controls most weeds, nematodes, soil insects, and other fungi and bacteria. |
| Water mold root rots (Phytophthora spp. * and Pythium spp. *) |
Plants wilt easily or suddenly collapse. Roots and crown become decayed. Also causes damping-off of seedlings. | Soilborne pathogens. Associated with poorly drained, waterlogged soils. Spores are spread in water. | Provide drainage and avoid excessive irrigation. Plant on raised beds. Seed treatments help to control the damping-off phase. An oomycete (water mold) specific fungicide may also be effective. |
| Virus or viruslike disease | Symptoms | Host range and natural spread | Comments on control |
| Mosaic (several viruses, including Impatiens necrotic spot virus and Turnip mosaic virus) |
Leaf mottling and flower breaking occur. Leaf symptoms vary with different viruses. White and yellow varieties do not show flower breaking. | In cruciferous weeds (mustard, wild radish, shepherd's-purse, etc.). Spread by aphids. Not seedborne. Symptoms favored by cool weather. | Destroy nearby weeds. Avoid fields near uncontrolled weedy areas. Plow under stock as soon as the crop is cut. Control aphids. |
| Stock is also susceptible to downy mildew * (Peronospora parasitica). | |||
| * For additional information, see section on Key Diseases. |