Black Rot (grape) - Disease Cycle

Disease Cycle

Guignardia bidwellii Disease cycle picture] The grape black rot pathogen overwinters in many parts of the grape vine and is able to over winter on the ground . In addition, pathogen can overwinter for at "least 2 years within lesions of infected shoots that are retained as canes or spurs."4 Rains release the overwintering spores(Ascospores) that form within mummies on the ground and can be blown by the wind.4 Some of the mummies on the ground can have a significant discharge of ascospores that begins about 2 to 3 weeks after bud breaks and will mature 1-2weeks after the start of bloom.4 A second type of spore (Conidia)can also form within cane lesions or mummies that have remained within the "trellis, and these are dispersed short distances (inches to feet) by splashing rain drops."4 Infection occurs when either of the spore types land on green grape tissue and tissue remains wet for a "sufficient length of time, which is dependent on temperature."4 The period that these overwintering spores are allowed to cause infection depends on the source.If there is a large source for infection, infection will set in early. In the presence of moisture, these ascospores slowly germinate, taking 36 to 48 hours, but eventually penetrates the young leaves and fruit stems (pedicels). The infections become visible after 8 to 25 days. When the weather is moist, ascospores will be produced and released throughout the entire spring and summer, providing continuous primary infection.