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Project description

Cultural Practices for Management of Verticillium Wilt of Strawberry in California. (98CC009)
Program UC IPM competitive research grants program
J.M. Duniway, Plant Pathology, UC Davis
Host/habitat Strawberry
Pest Verticillium Wilt Verticillium spp.
Discipline Plant Pathology
Cultural Controls
Start year (duration)  1998 (Three Years)
Objectives Characterize Verticilliam dahliae populations in strawberry cropping systems in California for biological diversity (vegetative compatibility) and variation in virulence on main strawberry cultivars.

Determine the relationships between inoculum of V. dahliae in soil and Verticillium wilt development in strawberry.

Evaluate effects of organic amendments on population dynamics of V. dahliae in soil and Verticillium wilt in strawberry.

Final report Because of the pending phase-out of methyl bromide, and possible complications of using other soil fumigants on a large scale, some nonchemical management options for Verticillium wilt in strawberry production were researched. Isolates of Verticillium dahliae, collected from major strawberry fruit and runner production areas of the state, were equally pathogenic on several strawberry cultivars, and had little diversity. Field and greenhouse experiments showed that threshold inoculum levels of V. dahliae at planting for subsequent disease development and yield loss in the strawberry cultivars Camarosa and Selva were about 0.3 and 3 microsclerotia per gram soil, respectively. Understanding thresholds for economic losses will enhance future cultivar deployment and may allow a risk assessment based on pre-plant soil assays. Although all California strawberry cultivars are susceptible to Verticillium wilt, several were found to differ significantly in severity of symptom development and yield loss. Field experiments near Watsonville showed that one-year rotations with crucifer crops and removal of strawberry debris did not reduce Verticillium wilt or enhance yield significantly in a subsequent strawberry crop. Field and greenhouse experiments were done to evaluate effects of high-nitrogen organic amendments on populations of V. dahliae in soil and Verticillium wilt in strawberry. Blood and fish meal at four and six tons per acre reduced pathogen populations in soil and/or disease incidence significantly, while the effects of feather meal at one to three tons/acre were variable. However, at the higher levels used amendments sometimes also caused phytotoxicity. Furthermore, soil amendments did not reduce disease development in the second year after application.

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