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Pythium damping-off
is the first seedling disease to occur in a growing season because this fungus
prefers cold soil temperatures and excess soil moisture. Germinated seed that
fails to emerge can be swollen, twisted and partially or wholly rotted. These
rots are often referred to as "water molds". The occasional plant that
does emerge may wilt, turn brown and die. Dead seedlings may be visible on the ground with
infected plants killed before the first true leaf stage. Plants often have a
rotted appearance. Leaves of infected seedlings are initially gray-green and
then turn brown. A few days later, the plants die. Diseased plants are easily
pulled from the soil because of rotted roots.
This disease is
extremely severe if excessive rainfall occurs immediately after planting. It has
been observed in well-drained and poorly drained soils; in sandy as well as
heavier soils; and in low and high organic soils. The disease appears
sporadically. It may occur in one part of a field in one year, but the following
year may appear elsewhere. Moreover, a second planting in a disease area may (or
may not) give a healthy stand.
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