| 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 methyl bromide‑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. more info * |
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. Mefenoxam applied at
transplanting will help get plants started. more info * |
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 methyl bromide‑chloropicrin or a nematicide or solarize soil.** |
| * For additional information, see section on Key Diseases. |
| ** For additional information, see section on Nematodes. |
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