Bed Fumigation for Preplant Management of Soil-borne Pathogens and Nematodes in Raspberry Fields

Raspberry growers in Washington frequently fumigate soil before planting to reduce soilborne pathogens and nematode populations during plant establishment. The EPA’s new soil fumigant reregistration eligibility decisions will affect use of most common soil fumigants, and include the establishment of buffer zones, areas excluding all but workers and handlers involved in the application. Structures within buffer zones may not be inhabited, but many berry fields are near or adjacent to homes. Buffer zones size can be substantially reduced by fumigating planting beds only and covering fumigated beds with an impermeable tarp. However, the long-term efficacy of bed fumigation in preventing re-colonization of treated areas by soilborne pathogens and nematodes is unknown. Five trials were established in commercial raspberry fields to compare bed and broadcast fumigation. Trials were established in randomized complete blocks, with 3 or 4 replicate blocks; one was non-replicated. In four trials, bioassays for the root rot pathogen Phytophthora rubi in the first year of growth indicated that soil from bed fumigated plots had no more P. rubi than that of broadcast fumigated plots. In the remaining trial, the bed fumigated plots had significantly (P < 0.05) less root rot than the broadcast fumigated plots. Root lesion nematode (Pratylenchus penetrans) population densities in bed-fumigated plots were lower than those in broadcast-fumigated plots in one trial (P < 0.05), and were statistically similar in all other trials. Plants in bed fumigated plots were more vigorous than those in the broadcast fumigated plots in one trial, and had the same vigor as the broadcast fumigated plots in the other trials. These first year results suggest that bed fumigation supports raspberry establishment as well as broadcast fumigation, with greatly reduced buffer zone size.