Effect of Sequential Crop Termination and Bed Fumigation on Verticillium dahliae Soil and Plant Density in Strawberry

Abstract

ABSTRACT Verticillium dahliae, the causal agent of Verticillium wilt of strawberry, is a major soilborne pathogen in California strawberry production. Recent shifts in disease management have necessitated alternative methods for disease control. Two field experiments were conducted to examine the efficacy of sequential fumigant applications for crop termination and bed fumigation to reduce Verticillium dahliae inoculum density in a naturally infested field. Fumigant efficacy was evaluated for crop termination and for reducing pathogen survival in host tissue. Crop termination was conducted using metam potassium and metam sodium. Bed fumigation was conducted using both metam products and chloropicrin. For plots that were subject to both crop termination and bed fumigation, inoculum levels were somewhat reduced (3–6 CFU/g of soil) but not to a level below the disease threshold for strawberry (2 CFU/g of soil). Plots subjected to crop termination with metam potassium and bed fumigation with chloropicrin resulted in the lowest V. dahliae inoculum density. Injury due to crop termination ranged from 53% to 77% at 7 days after fumigation (DAF) and 73–89% at 14 DAF. The odds ratio of V. dahliae survival in the terminated crop were lower than in crops not terminated and V. dahliae survival was less likely at 14, compared to 7 DAF. In the crop terminated with metam potassium, the odds ratio of pathogen survival in the petiole versus the crown was 0.9–1.4. This research shows that crop termination could constitute management strategies for Verticillium wilt of strawberry.