Effectiveness of nontarped broadcast fumigation and root removal on root lesion nematode and Fusarium and Pythium species in a red raspberry system

Authors: DEVETTER, LISA - Washington State University; WATKINSON, SEAN - Washington State University; Zasada, Inga; Weiland, Gerald - Jerry; Hesse, Cedar; WALTERS, TOM - Walters Ag Research

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2018
Publication Date: 7/1/2018
Citation: Devetter, L., Watkinson, S., Zasada, I.A., Weiland, G.E., Hesse, C.N., Walters, T.W. 2018. Effectiveness of nontarped broadcast fumigation and root removal on root lesion nematode and Fusarium and Pythium species in a red raspberry system. Plant Health Progress. 19(2):168-175. https://doi.org/10.1094/PHP-01-18-0006-RS.
DOI: https://doi.org/10.1094/PHP-01-18-0006-RS

Interpretive Summary: The majority of the processed red raspberries grown in the United States are produced in Washington. In this region, raspberry production is threatened by soilborne fungi and oomycetes (water molds) and plant-parasitic nematodes (microscopic worms), all of which reduce raspberry productivity and yield. Raspberry growers control these pests by injecting fumigants (volatile chemical pesticides) into the soil, but recent research has shown that this practice is often only marginally effective and the pests soon return to damaging levels. This research was conducted to determine whether removing root debris prior to fumigation improves disease management. Root debris from the previous crop can inhibit the movement of fumigants in the soil and may also protect pests from being exposed to the fumigant, thus leading to marginal disease control. A field experiment was conducted where roots were either removed or not from a raspberry field, and the field was then fumigated. Pest populations and raspberry yield were then determined. It was discovered that removing roots prior to replanting a raspberry field was not effective in reducing populations of any of the pests considered. Fumigation in this experiment initially reduced populations of plant-parasitic nematodes, but not fungi or oomycetes. These results are significant because they identify limitations to the current soilborne pest management system in raspberry and suggest that other fumigant formulations must be explored for better management for soilborne fungi and oomycetes. These findings will be used by researchers and raspberry growers to continue to improve current management practices targeting soilborne pests.

Technical Abstract: Improved methods for the preplant management of soilborne pathogens are needed in the red raspberry production system in the Pacific Northwest. This system is reliant on soil fumigation, a practice that has become heavily regulated and has also been observed to result in variable efficacy in some locations. Two experiments were conducted in commercial red raspberry fields in northwest Washington to: 1) evaluate the efficacy of a potato harvester, beach cleaner, and a Lundby plant lifter at removing root residues; 2) determine if the standard industry fumigation treatment 1,3-dichloropropene:chloropicrin (Telone C-35)® is effective against soilborne pathogens and plant-parasitic nematodes; and, 3) determine if root removal prior to fumigation and planting improves soilborne pathogen and nematode management. In the first experiment, the potato harvester was the fastest machine to remove roots, followed by the beach cleaner and plant lifter, with 91%, 96%, and 98% of root and crown material removed, respectively. In the second experiment, the efficacy of Telone C-35 soil fumigation without root removal (industry standard) was compared to fumigation with root removal (treatment of interest) and to non-fumigated plots with and without root removal (negative controls). Root removal did not improve fumigant efficacy. When only the main effect of fumigation was considered, population densities of P. penetrans, Pythium, and Fusarium in non-fumigated treatments were initially greater than in fumigated treatments, but this effect was lost over time, within six months of planting. However, the fumigation treatment did increase primocane production (8%) and fruit yield (12%) compared to the non-fumigated treatment. When the microbial community was considered, another fungal replant pathogen, Illyonectria (Cylindrocarpon) was found to be more dominant in the fungal community of non-fumigated roots/rhizosphere soil compared to fumigated; the role that Illyonectria may play in raspberry replant issues is unknown.