Fumigant Alternatives for Red Raspberry in the Pacific Northwest
Rachel Rudolph, Ph.D. student
Department of Horticulture
Washington State University
WSU Mount Vernon NWREC
The Pacific Northwest has the climate and growing conditions conducive for floricane
raspberry (Rubus idaeus) production. In recent years, however, raspberry plant survival has
declined significantly in the region. This decline can be partially attributed to severe pressure
from soilborne pathogens and pests, such as Phytophthora rubi and Pratylenchus penetrans,
which have been shown to contribute to reduced raspberry plant vigor, yield, and economic
returns. Chemical fumigation is a common method of management among raspberry growers.
Even though some fumigant products have been effective at controlling certain pathogenic and
pest populations, they do not address the issue of declining soil quality and have been shown to
suppress beneficial soil microorganisms. There are also many restrictions associated with
fumigants, such as buffer zones, posting requirements, worker protective equipment, and
constraining management plans. The following research projects are designed to test alternatives
to chemical fumigation that have potential to enhance soil quality in red raspberry field
production. Experiment 1 is a two-year field study evaluating the effects of ground covers on
pathogen/pest suppression, plant competition, and soil quality in established raspberry alleyways.
Nine ground cover treatments were seeded at recommended rates in the alleyways of an
experimental red raspberry field in Whatcom County, Washington in October 2014. The study is
a completely randomized design (CRD) replicated four times with a bare soil control.
Treatments will be evaluated based on physical, chemical, and biological soil quality parameters
including: bulk density, aggregate stability, infiltration, nutrient content/availability, organic
matter, and microbial community structure. Raspberry growth (cane diameter and density),
foliar nutrient content, yield, and berry weight will also be evaluated to assess plant productivity.
All ground covers selected for experiment 1 will also be evaluated for P. penetrans host
suitability in a greenhouse assay. Experiment 2 will evaluate pre-plant treatments of Brassica
seed meal (BSM) and chemical fumigation with or without root inoculum removal in a
commercial red raspberry field in Whatcom County. The experiment is arranged as a CRD with
four replications of four treatments. Declining raspberry plants were removed prior to treatment
application and the field will be replanted with raspberry in Spring 2015. The treatments include
the industry standard control of metam sodium fumigant with no root removal, BSM with root
removal, full-rate metam sodium with root removal, and half-rate metam sodium with root
removal. The treatments will be evaluated over two years with soil quality and plant
productivity measurements similar to experiment 1. This research will provide the academic and
red raspberry communities with valuable information regarding alternative management
practices that may be more environmentally sustainable and efficacious in controlling soilborne
pests and pathogens.