Purdue University
Department of Botany and Plant Pathology
Lilly Hall of Life Sciences
Plant Disease control

Strawberry Grey Mold
Paul C. Pecknold, Extension Plant Pathologist

Of several fruit rots of strawberry
in Indiana, only one is of major impor-
tance -- namely grey mold. This disease
is most prevalent in years when cool,
wet weather occurs during picking time,
or when heavy rains occur just before or
during harvest.

Symptoms

Grey mold generally starts on the
part of the berry that is in contact
with the soil or on berries that touch
other decayed fruits or dead leaves. It
is first noticeable as a light brown,
rather soft spot. In cool, moist weath-
er, the rot soon involves the entire
fruit, which then starts to dry out and
becomes firm and tough and uniformly
black in color. At this stage, infected
fruits will be covered with a grey
powder or dusty-appearing fungus
growth--the well-known grey mold. In
some seasons, strawberry blossoms may
become blighted by this disease, and
petioles and flower stalks may be af-
fected, resulting in serious injury to
the plant.

Cause

Grey mold is caused by the fungus
Botrytis cinerea which occurs in every
strawberry patch. The Botrytis fungus
survives on dead plant material and is
spread by windblown spores. Since this
fungus can live on almost any decompos-
ing plant material, it is common to all
production areas. Temperatures of 70 to
80° F and ample moisture favor the
disease. Frequent irrigation and/or
rain promote disease development.
Lush plant growth and cultivars
that have dense foliage that shade blos-
soms and fruit are most susceptible to
attack.

Control
Space plants properly so that air
can move freely between them. Promote
good air drainage by controlling weeds
and keeping beds thinned by renovation.
This allows rapid drying, which reduces
the probability of infection. Avoid
spring applications of excessive high
nitrogen fertilizer since this may pro-
duce excessive, thick foliage which will
prevent rapid drying of berries. Mulch-
ing, when practical, will also help
reduce the damage from fruit rot. Cul-
tivate as little as possible from bloom
until after harvest.

Regular applications of fungicides
will also help control fruit rots.
Spraying should begin when first blos-
soms start to open and be continued
every 7 to 10 days until harvest,
depending upon weather. If required,
sprays may be applied during harvest;
however, be sure to check label direc-

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