Seasonal development
and life cycle—Botrytis rot
The fungus that causes gray mold, Botrytis cinerea, survives in decaying plant material in or
on the soil and as sclerotia. Botrytis infects primarily through germination of its airborne spores.
An injury or dead or dying tissue must be present for the fungus to invade. On lettuce, aging wrapper
leaves or older leaves at the bottom of plants are usually first infected. Wrapper leaves often provide
entry sites for crown rot. Head rot may develop on sites damaged by aphids or downy mildew or other diseases.
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 Infection
in lettuce crown
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