Crop Profile for Strawberries in California - Regional IPM Centers

Description of Disease. Botrytis fruit rot is widespread. It can infect flowers on strawberry plants when
spores landing on them are exposed to free water and cool temperatures. Infections can either cause
flowers to rot or Botrytis can become latent. Latent infections resume activity on the berry later in the
season. Both green and red berries are susceptible, but ripening berries rot faster. During the growing
season, the fungus is constantly present.
Monitoring. Inoculum density and environmental conditions conducive to disease development (i.e.,
rain and cool temperatures) determine when fungicide applications are needed. Because these conditions
are usually seasonal, a protective application of a fungicide is used typically to prevent germination of
spores when conditions are ideal for disease development. Spray schedules thereafter are set according
to disease pressure and environmental conditions.
Controls
Control of Botrytis fruit rot ranges from repetitive fungicide treatments with no cultural control to
intensive cultural methods with limited or no fungicide applications. Environmental conditions in
various microclimates play an important role in determining control strategies. It is crucial to avoid or
delay the onset of fungicide resistance. It is common practice to rotate the use of fungicides between
chemicals that represent different chemical classes.
Cultural:
● Removal of Infected Material. Nothing can be done to escape the presence of this fungus, but
the level of inoculum in a particular field can be reduced by removing dead leaves and infected
fruit. Removal and destruction of dead or infected plant material reduces the amount of inoculum
capable of producing new infections.
● Canopy Size. The spacing between rows is an important consideration in mitigating the severity
of Botrytis fruit rot. Wider spacing allows for greater "breathing" room, conditions that do not
favor botrytis infestation. In addition, the management of plant (canopy) size can similarly open
up the space between plants, allowing "breathing" room and air circulation.
● Barriers/Mulches. Use of plastic mulches prevents berry-soil contact, thus reducing disease. For
organic growers, it is important to select growing areas that have environmental conditions that
are not conducive to disease development. Mulches that provide optimum air circulation may
also helpful in controlling the disease.
● Fertilizers. Excess fertilizer use, particularly too much nitrate fertilization, may enhance botrytis
fruit rot development and result in adverse production and quality impacts. These impacts may be
due to the effects on fruit integrity and strength.