Botrytis Bunch Rot Botrytis cinerea

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

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

4. 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).

5. 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.

6. 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.

7. 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.

8. 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.

9. 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

16. 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.

19. 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.

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

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

23. 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.

24. 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

33. 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

34. 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

35. 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

36. 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

37. 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