Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Raspberry -- Fruit Rot and Cane Botrytis
 
Cause: Botrytis cinerea, a fungus that causes blossom blight, preharvest rot, postharvest rot, and cane infections. On raspberry, it overwinters as sclerotia on canes and mycelia in dead leaves and mummified fruit. Sclerotia produce conidia in spring. A moist, humid environment is ideal for pathogen sporulation and spread. All flower parts except sepals are very susceptible. Initial infections of flowers are latent such that the fungus is dormant until fruit ripens. Fruit rot may be more prevalent in wet weather, in fields under overhead set irrigation systems, or where fruit ripens in the field for mechanical harvest. Conidia can infect mature or senescent leaves, resulting in primocane infections through petioles.
Symptoms: Rotted fruit, usually with tufts of gray fungus growing on surface. Receptacles of picked fruit also may be colonized and become gray with fungus spores. Pale brown lesions may appear on primocane leaves in mid- to late summer. Cane infections appear as tan to brown lesions often encompassing more than one node. Cane lesions exhibit typical concentric "watermark" patterns from fall through late winter. Sclerotia may be visible on canes as shiny, black, blister-like structures.

Note the concentric shades of brown on these canes and the black sclerotia.

The fruit rot and a fuzzy, gray mycelial growth develops.

 
Cultural control:

  1. 'Munger', 'Chilliwack', 'Comox', 'Fairview', 'Meeker', and 'Nootka' have shown moderate resistance to Botrytis fruit rot. 'Chilcotin', 'Meeker', 'Nootka', and 'Willamette' have shown resistance to Botrytis cane infections.
  2. Create an open plant canopy: use a double top wire training system, prune, avoid excessive nitrogen fertilization, and control weeds. These practices improve air circulation, increase light penetration, and speed drying of plant surfaces after irrigation and rain.
  3. Pick fruit in the coolest part of the day. Keep harvested fruit in shade while in the field, then move to cold storage as soon as possible.
  4. Control early-season primocanes.
  5. Adjust irrigation to early morning just before the sun rises so plants dry quickly. Switch from overhead to drip/trickle irrigation.
  6. Remove fall fruit during tying time.
Chemical control: Spray first at 5% bloom and then again 7 to 10 days later. Applications during the growing season, especially pre-harvest, aid control in wet weather. Thorough coverage and canopy penetration are essential.
  1. Captan 80 WDG at 2.5 lb/A. Do not apply within 3 days of harvest. 72-hr reentry.
  2. CaptEvate 68 WDG at 3.5 lb/A Do not apply more than two (2) consecutive application, within 3 days of harvest or more than 17.5 lb/A/season. 48-hr reentry.
  3. Elevate 50 WDG at 1.5 lb/A. Do not use more than 6 lb/A/season. Can be used up to and including the day of harvest. 12-hr reentry.
  4. Iprodione-based products plus another fungicide with a different mode of activity. Can apply the day of harvest. Note Fungal pathogens have shown resistance to iprodione when used exclusively. Tank-mix with other registered fungicides and limit to two (2) applications per year. 24-hr reentry.
    1. Iprodione 4L AG at 1 to 2 pint/A.
    2. Nevado 4F at 1 to 2 pint/A.
    3. Rovral 4 Flowable at 1 to 2 pint/A.
  5. 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.
  6. Switch 62.5 WG at 11 to 14 oz/A. May be used up to and including the day of harvest. Do not apply more than twice sequentially or use more than 56 oz/A/season. 12-hr reentry.
Notes: Other chemical(s) may be available under temporary, emergency use (section 18) or state crisis exemption labels. Double check with your local extension agent or chemical supplier.

Tests in western Washington have shown that the products Messenger and Serenade do not control this disease and are not recommended.

References:
Johnson, K.B., T.L. Sawyer, and M.L. Powelson. 1994. Frequency of benzimidazole- and dicarboximide-resistant strains of Botrytis cinerea in western Oregon small fruit and snap bean plantings. Plant Disease 78:572-577.

Ellis, M. A., Madden, L. V., Wright, S. R., Madden, L. V., and Wilson, L. L. 2008. Efficacy of pre-harvest fungicide applications and cold storage for post-harvest control of botrytis fruit rot (gray mold) on red raspberry. Online. Plant Health Progress doi:10.1094/PHP-2008-1015-01-RS.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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