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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Research Project #419092


Location: Crops Pathology and Genetics Research

2013 Annual Report

1a. Objectives (from AD-416):
1) Assess fumigants and rootstocks as Methyl Bromide alternatives in an existing walnut replant trial near Hanford, CA. 2) Establish a walnut replant trial near Chico, CA and prepare for another one near Stockton, CA to assess efficacy of fumigant and non-fumigant Methyl Bromide alternatives. 3) Facilitate economic analysis of walnut replant treatements. 4) Foster adoption and optimization of Methyl Bromide alternatives through educational outreach and exchange with California walnut producers and stakeholders.

1b. Approach (from AD-416):
Objective 1) On one to two occasions per year, nematode samples will be collected from soil at several spots in each plot. The samples will be collected from 0.5 to 2-ft depth at from each replicate rootstock x fumigation treatment subplot. For each sample, nematode extractions and quantifications will be completed for all nematodes potentially pathogenic to walnut. Each year, during tree dormancy, trunk circumference will be measured for all trees. Each year during the growing season, incidence of crown gall and other soilborne diseases will be determined by visual above-ground inspection. Objective 2) A new walnut replant trial will be established near Chico in Butte County in 2010. The orchard to be replanted will be cleared of trees in summer 2010 and pre-plant treatments will be applied in fall 2010. An attempt to make arrangements for a third walnut replant trial to be established in 2011 in the Stockton area of San Joaquin County. Objective 3) Provide treatment details for use in preparing cost-benefit analyses. Will w estimate walnut yields based on the PAR data collected for each replicate plot. The estimated yields will be used to facilitate the economic assessments. Objective 4) Field days will be organized by the UC Farm Advisors conducting the trials near Hanford, Chico, and Stockton after trees become established. A field day would be held for the Hanford trial in summer 2010, whereas days for the Stockton and Chico-area trials would be held in future years.

3. Progress Report:
This project was established in support of objective 1 of the in-house project, which is to demonstrate alternatives to methyl bromide (MB) in key crop systems and regions dependent upon MB. The goal of this project is to improve pre-plant fumigation strategies for walnut orchards and demonstrate the effectiveness of two MB independent alternatives. The most recent nematode data shows that the populations have raised substantially in all plots since the previous sampling at 244 days. The untreated plots remain highest in lesion, and the Telone II plus chloropicrin plot remains the lowest. The methyl bromide, Telone II plus chloropicrin, and Telone II plus methyl bromide treatments are generally similar and lower in lesion populations than the Telone II only treatments. Thus far, the Telone II strip and broadcast treatments are no different in lesion nematode number. The Vlach clonal paradox rootstock shows a trend towards lower lesion levels than the VX211 clonal paradox. These data are surprising, since a UC Nematologist, Riverside/Kearney Agricultural Center, Parlier, has reported VX211 tolerance to Pratylenchus under tank-trial conditions. His finding is supported by the levels recorded between VX211 and seedling paradox in the untreated plots of this trial, but there is no difference between them in the treated plots. The low lesion levels recorded in the Vlach may also be an anomaly created from fumigation overlap in the buffer area where these trees were planted. Unfortunately, space did not allow all three rootstocks to be included in the actual plot area. Fumigation has thus far significantly increased tree development, uniformity, and yield compared to the unfumigated plots. Clonal selections of paradox rootstock have also provided significant increases in tree growth and canopy size over standard seedling paradox. To date, no differences in tree development exist between the fumigated treatments, but the addition of chloropicrin to Telone has shown greater nematode suppression during the first four years of development compared to the other fumigated treatments. Telone under strip or broadcast also thus far performed as well as 400 pounds of methyl bromide broadcast. The results of this project have been presented at several field days and regional grower meetings. Fumigation of replant sites is occurring more frequently after growers saw the dramatic difference between the treated and untreated plots in this important Area Wide project.

4. Accomplishments