Grapevine Canker Diseases in California

Since Eutypa lata (Diatrypaceae) was first identified in California in 1975, grapevine cankers and consequent dieback have been attributed mainly to Eutypa dieback. However, research conducted in our laboratory in the past few years has shown that dieback of grapevines in California is complex and more than one fungal genus contributes to the dieback observed in the field. Our studies have shown that grapevine cankers can be caused by at least 25 different fungi in the Diatrypaceae, Botryosphaeriaceae, and Valsaceae families. Furthermore, field studies revealed the family Botryosphaeriaceae to constitute the main fungi isolated from grapevine cankers statewide and species such as Lasiodiplodia theobromae, Neofusicoccum parvum, Neofusicoccum luteum, and Neofusicoccum australe were shown to be much more virulent than the well-known pathogen E. lata. In addition, we have recently shown the pathogenicity of 8 different Diatrypaceae species on grapevines in California. Moreover, less known fungi associated with grapevine canker diseases in California such as Eutypella (Diatrypaceae) and Phomopsis (Valsaceae) species were also frequently isolated from grapevine cankers in table-raisin cultivars in both the San Joaquin Valley and Southern California and their role in grapevine health in California is currently under investigation. 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 during the past three years 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 sprinkler irrigation statewide. Botryosphaeriaceae spores were trapped frequently from the first fall rain through the last spring rains coinciding with September to April. Furthermore, 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 species. 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. Finally, our laboratory has developed chemical, cultural and organically acceptable control methods to reduce infections caused by these fungi. Accordingly, we have identified boron as an organic molecule for the control of E. lata. Additionally, we have proven the efficacy of several fungicides in reducing infection caused by at least 10 different fungi in 4 different families when apply as pruning wound protectants or as dormant spray applications. Furthermore, we have shown both double pruning and late pruning as a very effective cultural practice to reduce infections caused by both Diatrypaceae and Botryosphaeriaceae fungi in California. More work is being done to improve and implement single and combined applications of different active materials to control canker diseases. Finally, we showed that dormant application of fungicides with a penetrating surfactant did not cause significant phytotoxicity hazard to grapevines.