Recap of the 2015 Soilborne Diseases in Red Raspberry Field Day
By L.W. DeVetter1, R. Rudolph2, T. Walters3, J. Weiland4, and I. Zasada4
1Assistant Professor, Small Fruit Horticulture, Washington State University Northwest Research Extension Center (WSU-NWREC) in Mt. Vernon, WA
2Graduate Student and 5Scientific Technician, WSU-NWREC
3Agricultural Researcher, Walters Ag Research, Anacortes, WA
4Research Plant Pathologists, United States Department of Agriculture Horticultural Crops Research Unit in Corvallis, OR
We held our “Soilborne Diseases in Red Raspberry Field Day” in Lynden on Aug. 20, 2015. It was a great event and we extend our gratitude to our engaged audience, speakers, and host, Jon Maberry. This update provides a brief summary of what was addressed during the field day. Also, we want to make sure that the major take-home-messages from the field day are not misunderstood. We’ve come across several growers questioning current soil fumigation practices and considering the omission of soil fumigation between raspberry plantings. Although we highlighted weaknesses in current fumigation practices, there are large risks in not fumigating. We would only recommend considering this option for a small percentage of fields. The intention of our message was to inform growers that there are opportunities to improve the current approaches to managing soilborne diseases. Improved soilborne disease management approaches, including different methods of soil fumigation and fumigation alternatives, is an active area of research. We hope to provide the red raspberry industry with improved alternatives as a result of our research in the near future!
Below is a brief summary of all the presentations from the field day.
Lisa W. DeVetter (WSU Horticulturist) presented data from the first year of a project evaluating the effects of raspberry root and crown inoculum removal ("root removal") as a pre-plant strategy to improve management of soilborne diseases.
Three potential root removal devices were tested prior to soil fumigation in August 2014. Percentage of plant material
removed was 91%, 96%, and 98% for a beach cleaner, potato harvester, and plant lifter, respectively. The potato harvester was
the fastest root removal implement at 1 mph. The plant lifter was the slowest at 0.25 mph.
Populations of Fusarium spp. and Pythium spp. (used as a proxy for Phytophthora rubi) measured in November of 2014 were
initially lowest in the fumigation treatments, regardless of the practice of root removal or no root removal. Populations of
Fusarium spp. and Pythium spp. in the fumigated treatments were not different from nonfumigated treatments by February
of 2015, regardless of root removal.
By August 2015, root-lesion nematode populations had returned to pre-fumigation levels, regardless of treatment (i.e., root
removal with or without fumigation with Telone® C-35).
Data will continue to be collected through 2016 and will include an economic analysis. We will also be evaluating the impact
of root removal in a field with high Phytophtora root rot pressure.
Funding sources: Northwest Center for Small Fruits Research and Agriculture and Food Research Initiative Competitive Grant
no. WNP124321-001 from the USDA National Institute of Food and Agriculture.
Rachel Rudolph (PhD graduate student in Dr. DeVetter's program) introduced her PhD research, which started fall 2014 and spring 2015.
One experiment entails studying the effects of alleyway cover crops on soil quality and host suitability for root-lesion
nematode (Figure 1).
Rachel will also be comparing metam
sodium (Vapam®) to brassica seed meal
amendments alone and in combination
with root removal for managing soilborne
diseases and root-lesion nematodes.
She will also be looking at soil microbial
ecology changes as a function of
different soilborne disease management
Funding sources: The Washington Red
Raspberry Commission and Northwest
Agriculture Research Foundation.
Figure 1. Alleyway planted cover crops.
Tom Walters (Walters Ag Research) presented highlights from his research with fumigation alternatives in red raspberry.
In a heavily nematode-infested field, shallow-applied fumigants were more effective than nontarped deep fumigation.
Shallow-applied (shanked in at 5 and 10 inch depth, sealed with a smooth roller) Dominus® and Vapam® controlled root-lesion
nematodes better than deep-shanked Telone® C-35 and also promoted better initial growth (Table 1). Figures 2 and 3 show
the different rigs used for broadcast fumigation.
On the other hand, in a field with very little nematode infestation, a one-year rotation with white mustard controlled root-
lesion nematode well. In this field, the grower first verified that root lesion nematode numbers were low, that he had no
major weed problems, and that he saw no Phytophthora symptoms in the field before trying this approach. He planted a
winter grain cover crop in the fall following removal of the old raspberry crop, sowed white mustard in May, and mowed and
tilled it in the following August. He again planted a winter cover crop the following September, and planted raspberries this
past spring. So far, the raspberry crop is growing well and the root lesion nematode numbers are low. His good results have
probably come from choosing a low-pressure field to start with, from the year’s time for old raspberry roots to break down
before replanting, and from the white mustard incorporation.
Figure 2. Broadcast fumigation equipment.
Figure 3. Broadcast, shallow fumigation equipment.
Jerry Weiland (USDA-ARS) presented highlights from his pathology research with red raspberry and nursery crops.
Fusarium and Alternaria species isolated from cane lesions on red raspberry did not cause disease when inoculated onto
healthy ‘Meeker’ plants.
Comparison: Telone® C-35 without tarping is used in the raspberry industry, while forest nurseries use methyl bromide/
chloropicrin, metam sodium/chloropicrin, and other fumigants under VIF (virtually impermeable film) tarps.
Fumigation is much more effective in forest nurseries where tarps are used in reducing populations of Fusarium and Pythium
by at least 96%.
In contrast, soil populations of these pathogens are only reduced 10-42% in raspberry fields treated with similar fumigants but
without the use of tarps.
Conclusions: There is the potential to improve soilborne disease management in raspberry by applying Telone® C-35 as a
Inga Zasada (USDA-ARS) presented highlights from work done by her graduate student, Duncan Kroese.
Root-lesion nematodes can reside in old raspberry root material for up to 10 months after removing a raspberry planting.
Decline of nematodes in roots is more rapid if canes are treated with an herbicide.
Collection of soil cores down to 3 ft in raspberry fields before and after fumigation showed that root-lesion nematodes can
survive fumigation with Telone® C-35. At what depth depends on soil type.
As always, we want to thank the host of our field day, grower cooperators, Tim Purcell at Trident Agricultural Products, Inc., and the sources funding our projects.