botrytis bunch rot botrytis cinerea n.
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Botrytis Bunch Rot Botrytis cinerea

Botrytis Bunch Rot Botrytis cinerea

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Botrytis Bunch Rot Botrytis cinerea

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  1. Botrytis Bunch Rot Botrytis cinerea Dollars and Sense January 17, 2007 Santa Rosa, CA W. D. Gubler Department of Plant Pathology University of California, Davis

  2. Disease Triangle • Pathogen- Botrytis cinerea • Environmental Conditions • Host • Time

  3. Epidemiology • Fungus is ubiquitous • Fungus is a weak pathogen • Attacks juvenile tissue, highly succulent and senescent tissue such as blossom parts, ripe fruit and injured or dead tissues. • After infection the fungus can survive as a saprophyte on dead tissue or can produce sclerotia (resistant resting structure).

  4. Epidemiology • The fungus can be associated with debris on the vine or on the vineyard floor: • Sclerotia survive on canes or in fruit mummies. • Blossom debris • Sclerotia can survive adverse conditions. • Sclerotia germinate to produce conidia. • Conidial production favored by successive interrupted wet periods. • Conidia are dry and are dispersed by air currents or by water-splashing.

  5. Epidemiology • Infection occurs in dead and senescing flower parts and invades through the stamens into the flower receptacle. • Pathogen can also invade the necrotic areas around the abscission layer of the shredded calyptra on the receptacle. • Young berries generally resistant to infection due to epicuticular wax and chemicals in the wax.

  6. Why Disease?? • An outbreak of Botrytis bunch rot between véraison and harvest is regulated by a complex set of factors. • Of these, conidia dispersed in bunches and latent infection established at the berry base or receptacle during early season, and a stress factor(s), are the main factors responsible for symptom expression at véraison. • Climatic conditions such as high humidity, dew and intermittent rain during late season will regulate bunch rot development.

  7. Botrytis cinerea • The fungus always attempts to penetrate sound berries directly through the skin, but most of these penetrations are unsuccessful. • Skin damage (wind, birds, insects) thus also acts as a stress factor which offers another major pathway for the fungus to enter berries. • In the event of wounding, a combination of fresh wounds, freshly dispersed conidia and free water on the berry surface is necessary for successful wound infection. • A synchronization and combination of these events may not commonly occur in the vineyard.

  8. Symptoms • Can occur as 2 epidemics • Early mostly asymptomatic and occurring from pre-bloom to fruit set. • Brown-reddish lesions develop on leaves. Shoot dieback. • Blossoms become latently infected • However, not all infected blossoms result in disease • Later from pea-sized berries through harvest • Starts as browning of the skin of the fruit and invades other berries through cracks and wounds. • Berry leakage • Dry weather=lesions cease expansion • Wet weather=lesions continue to expand and fungus moves to other berries thru spore movement or mycelial growth

  9. Symptoms • Poorly hardened shoots may show bleaching in the fall with development of black sclerotia forming in bleached tissue. • This occurs mostly around nodes and suggests entry of the fungus through the petiole of a diseased leaf or through a leaf scar. • Sclerotia in mummified berries.

  10. Symptoms • Newly grafted grapevine cuttings held in high humidity and at temperatures of 30 C can be infected and quickly destroyed by Botrytis cinerea. • The fungus also may develop under the paraffin used to seal the graft union of grafted vines and inhibits development of the graft union.

  11. Control of Botrytis Bunch Rot • Fungicides • Leaf removal • Decreased fertilizer • Cluster Architecture • Trellising

  12. Fungicides • Timing • Bloom, Preclose, Veraison, Preharvest • Application • Full coverage, Both sides of vine, Preventative • Phenology • Blossoms, young fruit, older fruit, leaves, shoots • Weather • Rain

  13. Table 1. Results of Grape (J. riesling) bunch rot fungicide trial in Philo, 2004. Fungicides were applied at bloom ‘A’, bunch close ‘B’, veraison ‘C’, and 1 week preharvest ‘D’. 1Severity is the percent of each cluster affected by Botrytis rot 2Incidence is the percent of clusters with any rot. 3Values in a column followed by the same letter are not significantly different according to Fisher’s LSD t test at P=0.05.

  14. Canopy Management • Leaf Removal • Effect on fungicide application • Increases target site hit by 200x • Timing=berry set • Removes dead blossom debris, results in thicker wax layer • Later leaf removal results in sunburn, reduced epicuticular wax thickness • Hedging • Early Delays maturity • Late results in sunburn, Greenberry (Cladosporium cladosporioides) • Crown Suckering • Only small reduction in disease • VSP • Excellent Botrytis control if clusters are exposed

  15. Other Cultural Practices • If caught w/o fungicide application and can get in the vineyard • Use spray rig to spray high pressure directed air at clusters • Interrupts infection process • Must be done within 12 hours • If you don’t leaf remove • Use leaf blower-type directed wind to remove blossom debris early in season

  16. Cluster Architecture • Tight clusters more prone to rot • Berry touch reduces the epicuticular wax layer on the berry = easier access by pathogen • Extend rachis??? Gib, DMI fungicides • Reduce touching • Early exposure to sunlight • Increase wax thickness

  17. Fertilizers • Use of fertilizer can increase vegetativeness • Increase shade • Reduces wax thickness • Increase RH • Reduces wax thickness • Decrease Temperature • Increases favorable conditions for pathogen • Reduce wind speed • Increases favorable conditions for pathogen • Increase succulence of tissue • Easier infection of tissue

  18. What Happened in 2006 • Rain during bloom • Rain preharvest • Hang time • Rachis began to senesce • Rachis infected resulted in berry drop • Ripe fruit + water = Rot • Sound berries less effected

  19. What to expect in 2007 • Botrytis epidemics cyclic • 3 year cycle • 2007??? • Longer fruit exposed on the vine the bigger the chance of seeing disease • Early leafing • Fungicides if needed but always as a preventative treatment • Coverage!!! Best timing for good coverage is pre-close