Crop Profile for Strawberries in California - Regional IPM Centers

produce small, white powdery colonies on the undersides of leaves.
Description of Disease. Colonies of powdery mildew multiply to cover the entire lower leaf surface,
causing the edges of the leaves to roll up. Purple-reddish blotches appear on the upper and lower surface
of leaves. Infected mature fruits become seedy in appearance and support spore-producing colonies that
look powdery and white. The disease overwinters as mycelium on leaves in California, so it is most
likely introduced into the field through planting material or spores from neighboring fields. Ideal
conditions for infection are dry leaf surfaces, high relative humidity, and cool to warm temperatures.
Because of this, the disease is mostly limited to the coastal growing regions and northern nurseries, and
causes very little damage in inland growing regions.
Monitoring. Early signs of the disease are monitored since preventative control is most effective.
Applications are often tied to models based on meteorological observations.
Cultural:
Control
● Resistant Cultivars. Growers use resistant cultivars where practical. Use of these varieties is
typically region dependent with few of the varieties used in the central coast region being
resistant to powdery mildew. Statewide, the most common varieties used in production are all
relatively susceptible to powdery mildew.
● Overhead Irrigation. Overhead irrigation is avoided as it enhances the onset and severity of the
disease.
Biological:
● Ampelomyces quisqualis. 0 day PHI. Ampelomyces quisqualis (AQ10) is a biofungicide which is
a selective fungal hyperparasite. Use rates are from 0.5 - 1.0 oz/acre. This product works well
early in the season but is less effective in inland growing regions. It is also incompatible with
other fungicides so its use is usually limited to the early season in coastal growing regions.
Because this biological control is registered under FIFRA as a pesticide, it is also listed below
under Chemical controls for powdery mildew. The restricted-entry interval is 4 hours.
Chemical:
Controlling the disease on leaves with fungicides does increase yields, though losses are almost entirely
due to infection of flowers and fruit. Flower and fruit infections generally are the result of severe leaf
infections. Protective fungicides are used to protect flowers and fruit. Fungicides are applied about 1
month after planting and again 3 to 4 weeks later. Additional treatments are made when plants begin to