Grapevine Canker Diseases in California

Since Eutypa lata (Diatrypaceae) was first identified in California in 1975, cankers and consequently dieback of grapevines have been attributed mainly to “Eutypa dieback” in the State. However, in the past few years, our research has shown that dieback of grapevines in California is a much more complex situation than originally thought, and grapevine cankers can be caused by at least 20 different fungi in the Diatrypaceae, Botryosphaeriaceae, and Valsaceae families. Furthermore, our studies have indicated Botryosphaeriaceae fungi to constitute the main pathogens isolated from grapevine cankers statewide. In vitro pathogenicity studies in the laboratory as well as in vivo studies in commercial vineyards have shown all Botryosphaeriaceae spp. to be pathogenic. Moreover, 4 out of the 9 Botryosphaeriaceae spp. found in California appeared to be much more pathogenic than E. lata. In addition, species of Eutypella and P. viticola were commonly isolated from diseased vines from the table and raisin grape-growing regions of Southern San Joaquin Valley and Coachella Valley. Preliminary pathogenicity tests have suggested that these fungi constitute new pathogens in table grape areas capable of colonizing wood and producing cankers. Identification work suggested that these fungi may constitute new species and more work is being conducted to characterize these fungi.

Spore trapping studies conducted for the family Botryosphaeriaceae have allowed us to better understand the epidemiology of this new group of fungi in California. Spore trap studies have shown Botryosphaeriaceae spores to be mainly trapped following rainfall events and overhead and/or drip irrigation. Botryosphaeriaceae spores were trapped frequently after the first rainfall in September-October to March-April. These studies have allowed us to characterize low infection risk periods throughout the growing season and therefore, improving appropriate timing periods for pruning. Results from the spore trapping study conducted in Coachella Valley showed a high incidence of Eutypella spp. In this case it was documented that spore release occurred during sprinkler irrigation and also by drip irrigation. Surveys for the perithecia of Botryosphaeriaceae in California have shown various grapevine cultivars with perithecia of B. dothidea suggesting that the sexual stage could also play an important role in the epidemiology of the disease. More work is being done to understand the role of native and ornamental trees adjacent to vineyards in the epidemiology and disease cycle of canker diseases.

Our laboratory has developed chemical, cultural and organically acceptable control methods to reduce infections caused by these fungi. Double pruning was shown to be an effective cultural practice which completely eliminates canker formation by Diatrypaceae spp. We have now proved that this practice is also effective against the more rapidly moving Botryosphaeriaceae fungi. Finally, we showed that dormant application of Rally alone or in combination with Enable (another DMI fungicide) with a bark penetrant reduced infection by E. lata. Also, Rally treatments significantly also reduced Phaeoacremonium infection. More work is being done to evaluate single and combined applications of different active materials to control canker diseases. Finally, dormant application of fungicides with a penetrating surfactant was not a significant phytotoxicity hazard to grapevines.