Control of Fusarium Root Rot in Douglas-Fir Seedling Nurseries through Monitoring and Soil Amendments

Non-Technical Summary: The goal of this project is to enable forest seedling nurseries to stop using methyl bromide and reduce loss of Douglas-fir seedlings due to Fusarium root rot to less than 10%. The project will greatly improve monitoring of Fusarium commune, determine a threshold population for this newly recognized pathogen, develop effective alternative treatments based on green manure or other soil amendments, and promote the use of both new monitoring tools and effective soil amendment(s) by the nursery industry. The conifer seedling nursery industry currently produces over 80 million seedlings annually in Washington state alone. This industry is facing dire pressures from fungal diseases, combined with higher prices and tightening restrictions on chemical soil fumigants. Without fumigation seedlings are met with fungal disease complexes that dramatically reduce growth. The proportion of culled seedlings from nonfumigated soil commonly exceeds 50%. By far the most effective and common treatment over the last 40 years has been soil fumigation with methyl bromide between each seedling crop. However, because of safety and environmental concerns, methyl bromide use is increasingly restricted and expensive, leading to a current fumigation cost of roughly $2,000 per acre. The currently available test for Fusarium population in the soil does not reliably indicate true disease pressure, so nearly all nurseries fumigate between every crop as an insurance policy. This project will use new genetic information to develop a faster and far more accurate population test for pathogenic F. commune. This will make it possible to determine biological and economic thresholds of action which will reduce fumigation with less threat of economic loss. In addition, this new test will provide very fast assessment of whether fumigation or other treatment has been effective in reducing the disease risk. Several alternative soil treatments are promising, but understudied. This project will continue current trials of brassicaceous plant green manures, seed meals, and other soil amendments, to develop effective alternative treatments for Fusarium root rot. The quicker, more accurate Fusarium population test will be used to much more quickly assess these alternatives and develop a reliable alternative disease control protocol. Finally, this project will extend research-based information to nurseries through field days and a 2-day workshop to instill the use of improved methods. By developing tools, discovering methods, and supporting implementation of practical pest management alternatives to methyl bromide, this project will end the use of methyl bromide on over 1,000 acres annually and save growers over $1 million annually. Because the industry is integrally involved with the completion of the field research, results can and will be used immediately. It is expected that dissemination of this information will lead to a significant shift in nursery management within 2 years after project completion. <P> Approach: Methods: Objective 1. This project will use new genetic sequence information to develop a real-time PCR primer set, probe, and protocol that provides quantitation of F. commune. Multiple primer pairs will be designed that are potentially specific for F. commune. Primer pairs will be selected that indeed amplify of F. communae without amplifying F. oxysporum. Probes and a full RT-PCR quantitative protocol will be developed. Objective 2. In this objective we will determine threshold populations at which soil treatment is needed to prevent biological or economic damage. A combination of greenhouse, micro plot and field studies will be used to determine population of F. commune needed to cause unacceptable levels of root rot. One-year-old Douglas-fir seedlings will be planted into soils that infested with various levels of pathogen inoculum prior to planting. At the end of the growing season, seedlings will be lifted, graded using industry standard and evaluated for root rot. Figures will be developed relating RT-PCR output (population) at the time of planting to root rot damage. Objective 3. Materials with prior success or high potential to control fungal-caused replant disease, including green manures and seedmeals of the Brassicaceous plants B. juncea, B. napus, and Sinapis alba will be tested for capability to reduce severity of root disease infection and increase seedling transplant growth. A combination of micro plot and field studies will be initiated to determine the effectiveness of managing root rot caused by F. commune in methyl bromide fumigated and non-fumigated soil, using methods described in Objective 2, plus soil amendments. Data will be analyzed to test for effects of the amendments on disease development. Objective 4. Economic thresholds will be determined based on the crop value loss due to inaction at given pathogen populations, in comparison to methyl bromide and alternative treatments including brassica seed meal, compost, and green manures. To assess the net monetary benefits of alternative techniques we will prepare an enterprise crop budget for the production of Douglas-fir for each treatment. Along with yield differentials, treatments will be compared using a "green technology" framework that goes beyond purely monetary considerations to consider longer-term and external costs such as environmental impact. We will determine which method of production is the most cost efficient from a monetary (short-term) and "green" (long-term) perspective. Objective 5. This project will support 3 field days, held in each year of the project. These field days will highlight the field research and present oral briefings about the laboratory work. This project will support a workshop for conifer nursery growers in year 3, Transitioning from Methyl Bromide. The PIs will undertake the development of a crop profile. Evaluation: Activities will be evaluated individually for their immediate impact and as a whole by their effect on the adoption of new alternative tests and treatments. Individual events will be evaluated by standard pre- and post-event surveys of attendees.