Soilborne Pathogen and Nematode Management through Removal of Root Inoculum in Continuous Red Raspberry Systems

Soilborne pathogens and nematodes limit production of red raspberries (Rubus ideaus) in the Pacific Northwest of the United States and have been attributed to increasing reports of “replant disease.”  Newly implemented Reregistration Eligibility Decisions by the U.S. Environmental Protection Agency limit fumigation practices and current methods of disease and pest control are ineffective, leading to a decreased lifespan of crop productivity, an increased frequency of fumigation and replanting, and increased grower costs.  Growers need new and alternative techniques for effective management of soilborne pathogens and nematodes.  This project addresses this need by investigating the effects of root removal in continuous raspberry production systems.  Infested root and crown material remaining from the previous raspberry production fields likely serves as a reservoir of inoculum for subsequent plantings.  This project will evaluate the impacts of raspberry root removal on residual inoculum levels through two field experiments.  The first experiment began in August 2014, and compared three root removal devices, including a Lundeby plant lifter, a potato harvester, and a beach cleaner.  All pieces of equipment lifted approximately 98% of the root material to the surface for removal.  The potato harvester was the fastest to remove roots per linear distance, followed by the plant lifter and beach cleaner.  In a second experiment, efficacy of root removal to reduce soilborne pathogens and root lesion nematodes (Pratylenchus penetrans) was compared with and without fumigation using a split plot design, with fumigation as the main plot and root removal as the split plot.  This experiment was established in August 2014 and measurements are ongoing.  Comparison of pre- and post-root removal/fumigation treatments on P. penetrans revealed root removal reduced population densities by 99.8%.  Additional evaluations revealed Fusarium and Pythium populations were reduced through root removal (16% and 21%, respectively), but fumigation had a greater effect at reducing their numbers (41% and 64%, respectively).  The combined effect of root removal with fumigation was the most effective, and reduced Fusarium and Pythium by 64% and 69%, respectively.  Large roots remaining in control plots (without root removal) were colonized by both pathogens regardless of fumigation treatment, indicating that these roots serve as residual sources of inoculum. These data suggest root removal may have a role in an integrated pest management approach for the management of soilborne pathogens and nematodes in red raspberry.