Until recently, grapevine dieback in California was attributed mainly to the fungus Eutypa lata (Diatrypaceae). This fungus is known as the causal agent for Eutypa dieback. However, we have shown that dieback of grapevines in California is also caused by other fungi in the family Diatrypaceae (Eutypa leptoplaca, Cryprovalsa, Diatrype, Eutypella and Diatrypella) as well as by several species of Botryosphaeria, which appeared to constitute the main pathogens isolated from grapevine cankers statewide (Urbez-Torres, et al., 2006; Urbez- Torres, et al., 2007). This year, more species of Diatrypaceae have been identified from diseased grapevine. These included 5 species in the genus Eutypella collected in the table grape areas of the Coachella Valley. The common occurrence of these species in cankers as well as preliminary pathogenicity tests has suggested that these fungi constitute new pathogens in table grape areas. Identification work suggested that these fungi may constitute new species and more work is being conducted to characterize these fungi.
Isolations from cankers collected in the San Joaquin Valley have shown Phomopsis viticola to be the most common pathogen in table and raisin cultivars (Urbez-Torres, et al., 2006). Results from this year pathogenicity test have shown that Phomopsis viticola looks to be a grapevine wood pathogen capable of colonizing wood and producing cankers.
Results of spore trapping studies have shown that Botryosphaeria spores were mainly trapped following rainfall events in Mendocino, Napa, Colusa, San Joaquin, Monterey, and San Luis Obispo counties, and following overhead and/or drip irrigation in the Coachella Valley. Botryosphaeria spores were trapped frequently after the first rainfall in September-October to March-April. Interestingly, Botryosphaeria spores were sometimes trapped without rainfall or irrigation in Colusa County, suggesting that other environmental factors may contribute to spore release and/or spores were brought from other areas by wind. Results from the spore trapping study in Coachella Valley showed a high incidence of other fungi such as Eutypella species which were trapped together with B. rhodina. In this case it was documented that spore release occurred during sprinkler irrigation and also by drip irrigation.