Blueberries are an important economic and cultural crop in the Pacific Northwest. On the farms in this area, dagger nematodes carrying Tomato Ringspot Virus (TmRSV) caused a major production problem in blueberry fields in 2003. Presently, the first step in diagnosing nematode crop-production problems is to collect and identify the nematodes present in the soil and then to identify virus infection in the plant material. Special laboratory procedures are required to both isolate nematodes from soil or roots and for analysis of plant tissue.
The extent of dagger nematode distribution in the Island County is unknown, perhaps due to the difficulty in identifying it without specialized laboratory tests. All producers in the county need education and understating of methods for early detection and control of this problem.
This project investigated best management practices for economically containing and eradicating dagger nematodes from a functioning blueberry farm in the Pacific Northwest. The project tested the usefulness of two organic, environmentally friendly treatments (solarization and DiTerra) versus the standard chemical soil fumigant, Basimid. The four treatments (Basimid, DiTerra, solarization with 2 ml clear plastic, and a control) were randomly assigned to one-fourth of each of five adjacent rows. Soil samples were collected each year for both nutrient analysis and nematode counts, and plant samples were collected each year for both nutrient analysis and TmRSV infection each year.
Both soil and tissue test results indicate nutrient levels were sufficient for blueberry growth. An analysis of the ratio of dagger nematodes found in 2007 to those found in 2006 suggests there was no difference in efficacy between DiTerra and Basimid treatments resulted in no increase in nematode numbers while the control and solarization treatments led to a 4- to 10-fold increase.
Our project also endeavored to create a method of early visual detection of plants infected with TmRSV. Each plant in the study was assigned a visual health index from 1-5. We also recorded various visual descriptions of the plants and created a diagnostic tree to aid producers in identifying visible plant problems.
The most important outcome of the project was that local producers learned how to identify signs of the virus and to make site-specific treatments instead of the traditional blanket application of soil fumigants.
1) Investigate visual methods for identification of TmRSV infection
2) Investigate best management practices for economically containing and eradicating dagger nematodes
3) Investigate when to remove bushes and when to treat the soil with the appropriate methods
Soil test results indicate nutrient levels were sufficient for blueberry growth according to Oregon State University recommendations. Plant samples indicate nutrient management of the field is good in general. However, due to work performed for the project we discovered that copper and boron levels were low. As a result, major improvements have been made in getting additional amounts of those nutrients to the plants.
In the first year of the study, nematode sampling occurred in May after funding was approved. Sampling for nematodes should occur between December and late march, so we may have observed artificially low nematode counts in this year. Our second year sampling occurred in February. Dagger nematodes appear to have been well controlled with both the DiTerra and Basimid treatments.
Lesion, pin and cyst nematodes were well controlled by Basimid and all but the Pin nematode were well controlled by DiTerra. The solarization treatment did not control nematode population growth, probably because the treatment failed to raise soil temperatures to the required 105°F. Either we did not sufficiently seal the plastic to the ground or there was insufficient sunshine that season to raise soil temperatures adequately.
The two worst plants from each plot were sampled for plant virus testing each year. Tests revealed that only 17.5% of plants sampled had TmRSV in 2006. Ten percent of plant samples in 2007 had TmRSV. Plants were screened for at least TmRSV, shock, and scorch both years. We found only two viruses during the study: shock and TmRSV. The occurrence of shock increased dramatically in 2007, from 4.6% to 77.5%, probably due to a large uncontrolled aphid population in 2007.
Our results verify that dagger nematodes are associated with TmRSV. We found significantly more dagger nematodes in the soil of plants with TmRSV infection than those with shock or those without a virus.
The producers’ visual ratings appear to do a good job of identifying plants with TmRSV. The change in visual health rating from 2006 to 2007 indicates that plants with TmRSV have a 75% chance of getting worse and no chance of getting better. Plants with shock have only a 25% chance of getting worse and a 5% chance of getting better. Plants that had no virus have an 18% chance of getting worse the next year, probably due to an increase in shock, and a 10% chance of getting better.
BENEFITS OR IMPACTS ON AGRICULTURE AND PRODUCER ADOPTION
Several positive impacts resulted from this study. The producers learned that their field was low in copper and boron, but that in general the field nutrient levels were good. This indicates that fertilizer recommendations developed at Oregon State University are appropriate for Island County, Washington, growing conditions, where there is an increasing interest in blueberry production.
The producers also learned about the risk of their bushes contracting shock. This is important because shock is spread by bees and can infect other fields. This study provides all producers in the area with information that will reinforce knowledge of shock and its control.
The producers’ ability to differentiate TmRSV from other diseases by the end of the study will be useful to other producers who are moving into the blueberry production area. The producers are becoming recognized as experienced blueberry growers who are willing to share their expertise.
DiTerra is equally effective in suppressing dagger nematode populations, providing an organic alternative to toxic soil fumigants in the area. Now producers can use more sustainable, site-specific management techniques to control the dagger nematode.
REACTIONS FROM PRODUCERS
Involvement in this study has taught producers a great deal about optimal management of their field. Their commitment to organic and environmentally friendly production has increased greatly. Armed with a better understanding of plant disease they are positioned to manage their field in a more sustainable manner and are encouraged to continue learning more about sustainable agriculture.
RECOMMENDATIONS OR NEW HYPOTHESES
Though not an official part of this study, marigolds were planted in part of one bush row to evaluate their ability to suppress dagger nematodes as suggested in the literature. Preliminary results indicate this may be a very useful management tool. In addition, the marigolds suppressed weeds, a large issue for organic producers.
We want to expand this test of marigolds as both a dagger nematode-suppression and as a weed-management tool.
In August of 2007, we held a field day at the producer’s farm to talk about the results of this project. We made fliers and mailed them to a local producers and extension agents who expressed interest.