Presentation on theme: "Botrytis Bunch Rot Botrytis cinerea Dollars and Sense January 17, 2007 Santa Rosa, CA W. D. Gubler Department of Plant Pathology University of California,"— Presentation transcript:
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
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).
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.
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.
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.
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.
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
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.
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.
Control of Botrytis Bunch Rot ► Fungicides ► Leaf removal ► Decreased fertilizer ► Cluster Architecture ► Trellising
Fungicides ► Timing Bloom, Preclose, Veraison, Preharvest ► Application Full coverage, Both sides of vine, Preventative ► Phenology Blossoms, young fruit, older fruit, leaves, shoots ► Weather Rain
Table 1. Results of Grape (J. riesling) bunch rot fungicide trial in Philo, Fungicides were applied at bloom ‘A’, bunch close ‘B’, veraison ‘C’, and 1 week preharvest ‘D’. 1 Severity is the percent of each cluster affected by Botrytis rot 2 Incidence is the percent of clusters with any rot. 3 Values in a column followed by the same letter are not significantly different according to Fisher’s LSD t test at P=0.05.
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
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
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
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
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
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