| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Acremonium wilt (Acremonium strictum) |
Wilting, stunting, chlorosis and necrosis, often unilateral, of lower leaves. Vascular browning. Symptoms often develop with the onset of flowering. | Soilborne fungus. Disease is intensified if plants are stressed by excessive soil moisture. Fungus has a wide host range, including many weeds. | Plant disease-free plants. Fumigate soil with chloropicrin or a chloropicrin combination. |
| Cottony rot * (Sclerotinia sclerotiorum) |
Plants wilt and die. Basal stem rot. Cottony, white mycelium present in and on stems under moist conditions. Large black sclerotia form in and on stems. | Fungus survives in soil as sclerotia that germinate after a cold-dormancy period and produce airborne spores, which infect only dead or dying tissue. Direct infection from sclerotia may occur. Fungus has a wide host range. Optimum temperature for germination of fungus is 56° to 59°F and needs high soil moisture for at least 10 days. | Avoid planting in infested fields or fumigate soil. Carrots, celery, and lettuce are common hosts. Treat soil with PCNB before planting. Protect plants with thiophanate-methyl. |
| Fasciation (Rhodococcus fascians) |
Short, swollen clumps of distorted shoots that do not elongate at the base of plants. Vigor of plant is reduced. Secondary rotting of clumps may kill plant. | Bacteria survive on infected plants and debris. Bacterium has a wide host range. Spreads in water. | Plant disease-free plants. Avoid injuries to base of plant, especially when plant is wet. Control is difficult; plants may have to be discarded. |
| Leaf spot* (Septoria leucanthemi) |
Brown, circular and irregular spots on leaves. Heavily infected leaves yellow and die. Minute black dots (pycnidia) are visible in the center of spots. | Fungus survives on infected plants and debris. Spores are spread by splashing water. Pathogen needs condensed moisture to germinate and infect. | Use disease-free plants. Rotate land for 2 years. Avoid overhead irrigation and cultural operations when foliage is wet. Protect plants in rainy weather with chlorothalonil or thiophanate-methyl. |
| Pythium root rot * (Pythium spp.) |
Plants stunted as a result of reduced root system. Small roots rotted. | Soilborne pathogen. Spores spread with soil and water. Favored by excess soil moisture and poor drainage. | Avoid poorly drained soils. Plant on raised beds. Reduce amount of irrigation water. An oomycete (water mold) specific fungicide applied at transplanting will help get plants started. |
| Root knot nematode ** (Meloidogyne hapla) |
Plants are stunted. Swellings or galls on roots. | Nematodes survive in soil as eggs. Disease is usually most severe in sandy soils and in warmer climates. | Preplant fumigate soil with chloropicrin/chloropicrin combination or a nematicide or solarize soil. |
| * For additional information, see section on Key Diseases. |
| ** For additional information, see section on Nematodes. |