Grape black rot affects many grape growers throughout the United States and most the other warm and arid grape growing areas world wide, therefore, it is important to understand the disease life cycle and environmental conditions to best manage the disease. Once infection takes place, different methods are available to control the disease.
Biology: The grape black rot pathogen overwinters in many parts of the grape vine and is able to over winter on the ground especially in mummies. In addition, pathogen can overwinter for at "least 2 years within lesions of infected shoots that are retained as canes or spurs." Rains release the overwintering spores (Ascospores) that form within mummies on the ground and can be blown by the wind. 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. 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." 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." 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.(Wilcox, Wayne F. "Black rot Guignardia bidwellii." Disease Identification Sheet No. 102GFSG-D4. 2003. Cornell. 24 Oct. 2010 )
Environmental conditions for infection: When the weather is moist, ascospores are produced and released throughout the entire spring and summer, providing continuous primary infection. The black rot fungus requires warm weather for optimal growth; cool weather slows its growth. A period of 2 to 3 days of rain, drizzle, or fog is also required for infection." (Ries, Stephen M. "IPM : Reports on Plant Diseases : Black Rot of Grape." Integrated Pest Management at the University of Illinois. Dec. 1999. 24 Oct. 2010 ) "Conidia spores can also form, within cane lesions or on mummies that have remained within the trellis, and these are dispersed by splashing rain drops.” (Wilcox, Wayne F. "Black rot Guignardia bidwellii." Disease Identification Sheet No. 102GFSG-D4. 2003. Cornell. 24 Oct. 2010 ). Raindrops transfer these spores by moving the spores to different plant parts, especially susceptible young leaves. “If water is present, the conidia germinate in 10 to 15 hours and penetrate young tissue. New black rot infections continue into late spring and summer during prolonged periods of warm, rainy weather. The conidia are capable of germinating and causing infection several months after being formed. During August, the pycnidia are transformed into an overwintering stage that, in turn, gives rise to pseudothecia within which the spring spores (ascospores) are produced. This (ascospore) is "forcibly discharged into the air and can travel considerable distances". Research has shown that ascospores are an important source of primary infections in the spring. In the spring during wet weather, the "pycnidia on infected tissues absorb water and conidia are squeezed out.""Conidia are splashed about randomly by rain and can infect any young tissue in less than 12 hours at temperatures between 60-90 degrees."5. (Ellis, Michael A. "Fact sheet Agricultural and Natural Resources: Grape Black Rot." Department of Plant Pathology. The University of Ohio State Extension. 2008) A film of water on the vine surface is necessary for the infection to inoculate. This completes the disease cycle.” (Ries, Stephen M. "IPM : Reports on Plant Diseases : Black Rot of Grape." Integrated Pest Management at the University of Illinois. Dec. 1999. 24 Oct. 2010 )
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