|Disease (causal agent)
||Survival of pathogen and effect of environment
||Comments on control
|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.
|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.
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 *
|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.
|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
|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
|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.