| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Cottony rot * (Sclerotinia sclerotiorum) |
Plants wilt and die. Basal stem rot. Cottony, white mycelium present in and on stems under moist conditions. Long, black sclerotia form in and on stems. | Fungus survives in soil as sclerotia, which germinate after a cold-dormancy period to produce airborne spores. Direct infection from sclerotia may occur. Fungus has a wide host range. Favored by overhead irrigation and high humidity. | Avoid planting in infested fields or fumigate soil. Treat soil with PCNB before planting. Carrots, celery, and lettuce are common hosts. Irrigate early in the day so plants dry quickly. Spray base of plants and lower foliage with thiophanate-methyl. |
| Crown gall * (Agrobacterium tumefaciens) |
Spherical galls on stems most often at base of plant. Heavily infected plants are stunted. | Soilborne bacterium with a wide host range. Survives in soil for several years. | Plant disease-free plants. Propagate from clean plants. Dip or spray cuttings with Agrobacterium radiobacter 'K84' immediately if wounded. Avoid wounds, especially when plants are wet. |
| Downy mildew * (Peronospora radii) |
Young tip leaves are dull green, severely stunted, and roll downward. Gray-purple fungus grows on undersides of leaves. Disease is common on seedling phase; large plants are less frequently attacked. Infected plants fail to produce flowers. | Thick-walled resting spores (oospores) in dead plant parts. Airborne spores. Favored by cool (40° to 60°F), wet weather. | In greenhouse, reduce humidity. Drench seedlings with an oomycete (water mold) specific fungicide. Do not replant in fields where disease has been severe. Steam treat to kill resting spores. Protect foliage with mancozeb. |
| 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. Galls have lateral roots. | Nematodes survive in soil as eggs. Disease is usually most severe in sandy soils. Also prevalent in cooler climates: optimum temperature to invade roots is 59° to 68°F (15° to 20°C) and for growth and reproductions is 68° to 77°F (20° to 25°C). | Preplant fumigate with chloropicrin or a chloropicrin combination or solarize soil. |
| Root lesion nematode (Pratylenchus spp.) |
Plants are stunted. Necrotic lesions on roots that involve the cortex and deeper tissues. | Nematodes survive in soil as adults, larvae, and eggs. | Preplant fumigate with chloropicrin or a chloropicrin combination or solarize soil. |
| Southern blight * (Sclerotium rolfsii) |
Plants wilt and collapse. Basal stem and roots are rotted. White cottony fungus growth may be present on infected parts and soil. Small (0.625 inch), tan or brown sclerotia form on rotted tissues and in soil. | Sclerotia survive in soil. No airborne spores are formed. Sclerotia germinate and infect susceptible plants. Fungus has a wide host range. | Avoid fields where the disease has occurred or fumigate with chloropicrin or a chloropicrin combination. PCNB applied to the base of plants or as a preplant treatment will help. |
| Marguerite Daisy is also susceptible to powdery mildew * (Golovinomyces cichoracearum), Verticillium wilt * (Verticillium dahliae), leaf spot (Ramularia sp.), curly top (Beet curly top virus), and aster yellows (Aster yellows phytoplasma). | |||
| * For additional information, see section on Key Diseases. |
| ** For additional information, see section on Nematodes. |