Seasonal development
and life cycle—Phytophthora root and crown rot
The fungus that causes Phytophthora root and crown rot survives
in soil as spores (oospores) for several years. Water, temperature,
and soil texture are the major factors affecting the development
of root and
crown rot. The presence of water is mandatory; soil saturation
for as little as 5 to 6 hours can result in infection.
Optimum temperature for plant infection is 75° to
92° F. Contaminated seed and transplants
or soilborne inoculum are sources of primary infections.
Irrigation water often disseminates fungal propagules from
infested areas to other parts of the garden. Increased frequency
and duration of irrigation favor
disease development. Symptoms usually appear following a
warm, wet period. The disease is severe in fine-textured
soils that drain slowly and in highly compacted soils. The
Phytophthora species that attacks peppers and
eggplants also affects tomatoes.
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Browning
of inner root tissue
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