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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Crops Pathology and Genetics Research

2012 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 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 University of California 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 objective 1 of the in-house project, which is 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. All of the fumigated plots have grown extremely vigorously, and give local walnut growers the impression that the Tulare English scion is four years old, rather than its actual three years. The non-fumigated plots, as mentioned previously, are noticeably smaller and less uniform in growth. During the 2011 season, the fumigated plots consistently produced 12-14 foot of growth. Because of the high vigor, the principle investigator directed the grower to delay pruning of the experiment until mid- April of 2012, when one to two inches of shoot growth had already developed. Delayed pruning of walnut is a horticultural technique used on highly vigorous trees to improve lateral bud break and reduce early season vigor somewhat. The principle investigator personally instructed and supervised the pruning by two of the grower’s employees. The trees were also minimally pruned in order to take advantage of the 2011 growth, which proved to be highly fruitful in 2012. The crop on the fumigated trees is estimated at 1000-1200 pounds per acre, which is definitely worth harvesting, since walnut prices are presently about $1.50 per dry, in-shell pound. This would also demonstrate that fumigation brings replant walnut trees into production at least two years ahead of non-fumigated trees. The month of June experienced unseasonably severe winds for the San Joaquin Valley, gusting over 40 miles per hour during June 5-7. This unfortunately resulted in damage to the heavily cropped Methyl Bromide experiment. The trial was surveyed by the PI two days after the event, and damaged trees were rated for the percentage of canopy lost from limb breakage. A total of 60 trees suffered damaged. Nineteen trees lost suffered 2-10 % canopy loss. Twenty-four trees lost 15-30% of their canopy, eleven trees lost 40-60%, and six trees suffered 70-100% canopy loss. This unforeseen event proved very frustrating for both the researchers and the grower cooperator, who now questions the wisdom of the lighter pruning, since he is a traditionally severe pruner in his other blocks. However, the pattern of the damage suggests that a large whirlwind may have traversed the block, causing most of the loss. Hopefully, the high yield on the remaining undamaged trees will compensate for the wind loss. As mentioned previously in this report, the high vigor of the fumigated trees on VX211 and Vlach has made this project a real horticultural challenge. Scientists from University of California Davis have agreed to perform another round of light bar readings this August. This is now very important, since it will help in adjusting the yield data to the percent shaded area existing per plot. The loss of trees early in the trial, along with the recent wind damage, may make such a correlation necessary for accurate yield comparisons between treatments. Nematode sampling of each plot and rootstock in one-foot increments to a depth of five feet is planned for this fall. Harvest data will also be taken mid-September, and the results will be presented at the 2012 MB Alternatives Conference in Florida in November.

4. Accomplishments

Last Modified: 06/26/2017
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