- Vegetables: broccoli, brussel sprouts, cabbages, cauliflower, rutabagas, turnips
- Crop Production: crop improvement and selection, crop rotation, food product quality/safety, nutrient management, organic fertilizers, tissue analysis, varieties and cultivars, water management
- Education and Training: decision support system, extension, farmer to farmer, networking, on-farm/ranch research, participatory research, workshop
- Farm Business Management: risk management
- Pest Management: chemical control, cultural control, economic threshold, genetic resistance, integrated pest management, sanitation, trap crops
- Production Systems: agroecosystems, holistic management, integrated crop and livestock systems, organic agriculture
- Soil Management: soil analysis, soil chemistry, soil quality/health
- Sustainable Communities: local and regional food systems, social networks, sustainability measures, urban agriculture
“In the past 3 years [2009-12] we have had a 25% loss in our brassica crops due to clubroot, costing us between $60-80,000 in lost revenue per year. We are running out of clubroot free ground on which to rotate brassica crops.”
David Egger, fresh market vegetable grower, Portland, OR
“We have stopped growing brassicas on 15% of our land due to clubroot.”
Corey Dickman, processed vegetable grower, Mt. Angel, OR.
A survey sent to farmers in in Oregon’s Willamette Valley in 2012 showed that David’s and Corey’s experiences with clubroot’s damaging effects are not isolated or unique. Clubroot (causal organism, Plasmodiophora brassicae) is a major disease of brassica crops (i.e., broccoli, cabbage, cauliflower, Chinese cabbage, rutabaga) and is causing significant crop losses. The goal of this project is to identify the most effective and economical clubroot control strategies and to provide farmers with the necessary resources so they can implement a successful control program.
Brassica farmers in the Pacific Northwest (PNW) are increasingly worried about clubroot. So much so that in 2014 NW Agricultural Research Organic Committee members (growers and industry personal from five NW Washington counties) identified clubroot as being in the top 15 research priorities for 2015-19. Incidence and severity of the disease is increasing due to 1) increased production of forage radish and turnip cover crop seed to meet Midwest demand, 2) the increasing number of vegetable farmers with a 15 or more year history of intensive, short-rotation production, 3) an increase in the proportion of land planted to brassicas on vegetable farms (as consumption increases due to their health benefits), and 4) increasing acreage planted to overwintering brassica crops (as winter markets increase).
Dealing with clubroot is challenging. Thick walled resting spores can remain viable in soil for 17+ years, making it difficult if not impossible to eliminate the pathogen from an infested field. Therefore, once pathogen populations have developed to levels that cause economic damage, the goal is to manage rather than eradicate the disease. Control measures include liming to raise the soil pH to ≥7.0; rotation with non-host crops on a six to eight year cycle (preventing build-up of high pathogen populations); planting resistant varieties; applying boron; and irrigation and soil management to reduce the likelihood waterlogging.
One promising solution is to plant clubroot resistant varieties, but currently few varieties are available in the U.S. In Europe where they have been dealing with clubroot for centuries, seed companies have recently developed clubroot resistant varieties for cabbage and cauliflower, but some of these varieties have not been tested here and are not available in the U.S. Because there are many races of the pathogen, these varieties must be tested for resistance to the dominant races present in the PNW.
Several cultural practices show some benefit in reducing the economically damaging effects of clubroot, including applying boron and soil pH management. Of these practices soil pH management may be the most practical and effective control measure. Liming the soil to a pH of ≥7.0 has been shown to be effective in reducing infection rate and disease severity. In 2012 we surveyed a group of 37 conventional and organic fresh market and processing vegetable farmers in western Oregon about the importance of clubroot and their experiences with pH manipulation. Nineteen farmers responded, and all agreed that pH manipulation had the potential to control clubroot. However, they lacked specific recommendations on how to efficiently and cost-effectively lime to high pH (at a pH >~6.7 a soil’s lime response become non-linear and traditional liming recommendations may not be appropriate), or how they could evaluate pH on-farm in to assess if their target pH was reached.
Ideally this disease should be managed through rotation, but many organic and mid-size fresh market growers do not have enough land to be able to implement six+ year rotations, especially due to the high market demand for brassicas. However, we have been collecting detailed rotation histories from long-term vegetable farms in this region and scouting those farms for clubroot, and those data suggest that risk of serious clubroot damage is significantly reduced with a five year rotation. If true, this length of time may be more realistic for growers to implement.
In close partnership with farmers in western Oregon this project will: 1) Screen clubroot resistant brassica varieties for resistance to races of the pathogen found in the PNW and evaluate their horticultural performance, 2) Evaluate the effectiveness and practicality of various cultural practices to reduce the economically damaging impact of clubroot, 3) Evaluate the effectiveness of integrated management (resistant varieties plus cultural practices), 4) Identify the minimum rotation required to reduce clubroot risk to acceptable levels.
Through collaborative, on-farm reasearch, we anticipate that this project can identify the most effective and economical clubroot control strategies and provide producers with the necessary resources to be able to implement a successful control program.
Project objectives from proposal:
The goal of this project is to provide farmers with the resources and knowledge necessary to implement an effective and economical integrated clubroot management program. The farmer-scientist team will conduct collaborative research and Extension activities:
1) Objective: Conduct on-farm research investigating cultivar resistance to clubroot and the effectiveness of cultural practices for clubroot suppression.
Outputs: On-farm trials will address the components of clubroot disease management, including variety selection, soil pH management, and boron application. Working with farms that have a history of clubroot, we will collect field rotation records to determine the relationship between rotation length and clubroot severity.
Performance Target: Based on the findings of variety screening, cultural control, and farm rotation studies, we will develop integrated recommendations for clubroot disease management.
2) Objective: Provide Extension outreach to growers to assist them in developing an integrated approach for clubroot disease control.
Outputs: The following learning resources will be produced by the project: 1) a guide with the relative resistance and horticultural performance of clubroot resistant varieties screened, 2) an integrated clubroot management Extension publication, 3) a clubroot information ''portal'' at Oregonvegetables.com, and 4) an eOrganic webinar.
Performance Target: During the final year of the project, we will assess changes in farmer understanding, intentions, and practices. Farmers will be asked to identify specific practices they have adopted or intend to adopt as the result of this project. For each strategy, farmers will describe 1) whether or not they adopted it or if they intend to adopt it, 2) if it appears to be effective (if they adopted it), and 3) if it is cost effective. Farmers will also be asked how much damage and lost income they experienced due to clubroot before the project, and how much damage and lost income they anticipate after adopting project findings.