Page Banner

United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Crops Pathology and Genetics Research

2011 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
Established in support of Obj. 1 of the in-house project, the goal being to demonstrate alternatives to 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. Beginning January 17, 2010, an extensive 3-day nematode sampling was performed on each of the three rootstocks and 36 plots in 1 ft-increments to a depth of 5 ft. Samples from each stock were submitted separately and daily to the lab to prevent any chance of misidentification. On October 27, 2011, trunk caliper diameters were taken approximately 12 in. above the soil surface on all trees within the trial. The data collected during this reporting period shows that the nematode populations have risen substantially in all plots since the last sampling 244 days previous. The untreated plots remain highest in lesion numbers, and the Telone II plus chloropicrin plot remains the lowest. The mebr, Telone II plus chloropicrin, and Telone II plus mebr 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 at the Riverside/Kearney Agricultural Center has reported VX211 tolerance to Pratylenchus under tank-trial conditions. This 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. Further investigation into the rootstock/Pratylenchus interaction is planned under the direction of the UC nematologist. As mentioned previously in this report, the untreated plots also represented a very high % of the tree loss after the first two growing seasons (77.5%). Tree size in all the treated plots is very similar, with the strip treatment of Telone II being 5.3% smaller than the average of the other treated plots. Statistical analysis is in progress in preparation for the 2011 MeBr Alternatives Conference in San Diego. A photoelectric light bar scan of the entire trial is planned for 08/11 to further delineate any differences in rootstock and treatment canopy size. Ultimately, yield data will serve as the great and final integrator of fumigant performance. Yield data collection may commence as early as next season, depending upon fruit set. This project is monitored by maintaining a complete file of the agreement, reviewing the annual reports, and conducting meetings with the cooperator during the course of the agreement

4. Accomplishments

Last Modified: 06/22/2017
Footer Content Back to Top of Page