Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Gooseberry and Currant -- Powdery Mildew
 
Cause: Podosphaera mors-uvae (formerly Sphaerotheca mors-uvae), has been reported on Ribes sp. in the Pacific Northwest; the former is found more commonly. The black overwintering structures, called chasmothecia, form on canes and twigs. Ascospores are released around bloom. Conidia can be produced within 10 days on infected leaves and contribute to multiple infections during the growing season. The black currant cultivars 'Ben Nevis', 'Magnus', and 'Tsema' were very susceptible to this disease at Mt. Vernon, WA.
Symptoms: The fungus appears as a white powdery growth on the leaf surface, green shoots, and particularly fruit. Infected plants often are stunted. As fruit matures, the mildew changes to a dark brown coating with tiny black specks (chasmothecia) that render the berries unmarketable. Infected fruit often crack open and rot.

Gooseberry fruit with gray patches and splits.

As the gooseberry fruit matures, the mildew changes to a dark-brown coating that renders the berries unmarketable.

Notice the diseased currant fruit are small and discolored.

This close up picture shows cleistocarps of the powdery mildew fungus.

 
Cultural control: Plant resistant cultivars. The red currant cultivars 'Minn 69' and 'Viking', the white currant cultivars 'Blanka', 'Mason's', and 'Primus' and the black currant cultivars 'Ben Alder', 'Titania', and 'Ben Tirran' have shown little, if any, symptoms at Mt. Vernon, WA.
Chemical control:

  1. Delayed dormant (green-tip stage) - lime sulfur at 2.5 gal/100 gal of spray. 48-hr reentry.
  2. Apply at prebloom as blossoms are ready to open, at full bloom, and 2 weeks later.
    1. Abound at 6 to 15.5 fl oz/A. Pest not on label but product will control powdery mildew if used before symptoms are observed. Do not apply more than twice sequentially or more than three times per year. May be applied on the day of harvest. 4-hr reentry.
    2. Armicarb 100 (85% potassium bicarbonate) at 2.5 to 5 lb/100 gal water is registered for gooseberry. Might supplement a normal program when powdery mildew is first observed. Do not mix with acidifying agents. Thorough coverage is essential. Washington and Idaho only. 4-hr reentry.
    3. Cabrio EG at 14 oz/A. Use before symptoms are anticipated. Do not apply more than twice sequentially or more than four times per year. May be used at harvest. 24-hr reentry.
    4. Kaligreen (82% potassium bicarbonate) at 2 to 3 lb/A is labeled for currant. Might supplement a normal program when powdery mildew is first observed. Do not mix with other pesticides. Thorough coverage and frequent applications are essential. 4-hr reentry.
    5. Kumulus DF (80% sulfur) at 6 to 15 lb/A. 24-hr reentry.
    6. Microthiol Disperss (80% sulfur) at 6 to 15 lb/A. Do not use a spreader sticker. 24-hr reentry.
    7. Pristine at 18.5 to 23 oz/A. Do not use more than 2 consecutive applications or more than 4 times/year. Can be used day of harvest. 12-hr reentry.
    8. Propiconazole-based fungicides are registered. Do not use more than 30 fl oz/A/season or within 30 days of harvest.
      1. Orbit at 6 oz/A. 12-hr reentry.
      2. PropiMax EC at 6 fl oz/A. 24-hr reentry.
      3. Tilt at 6 fl oz/A. 12-hr reentry.
    9. Rally 40 WSP at 5 oz/A. Applications may be made up to the day of harvest. Do not apply more than 40 oz/A/season. 24-hr reentry.
    10. Safer Garden Fungicide (Ready To Use 0.4% sulfur) thoroughly sprayed over the entire plant. For currants only. Do not use when the temperature is over 85°F or within a few weeks of an oil spray. Can be used up to 1 day before harvest.
    11. Thiolux Jet (80% sulfur) at 6 to 15 lb/A for gooseberries and at 5 to 10 lb/A for currants. 24-hr reentry.
Biological control: Sonata (Bacillus pumilis strain QST 2808) at 2 to 4 quarts/A. May be applied up to and including the day of harvest. 4-hr reentry.
References:
Purnell, T.J. and A. Sivanesan. 1970. Sphaerotheca mors-uvae. CMI Descriptions of Plant Pathogenic Fungi and Bacteria, No. 254. Surrey, England: Commonwealth Mycological Institute.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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