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United States Department of Agriculture

Agricultural Research Service

Research Project: Optimization of “Horn” Phosphine Fumigations to Retain California Walnut Exports

Location: Commodity Protection and Quality

2013 Annual Report


1a.Objectives (from AD-416):
Ensure pest-free security and food safety of walnuts in postharvest marketing channels via the development of efficient, economical, and environmentally benign chemical treatments. Retain and expand export of California-grown walnuts. Collect insecticidal efficacy data using the “Horn” Vaporphos phosphine fumigation system and optimize to specifically address the rapid through-put processing demands of the walnut industry.


1b.Approach (from AD-416):
Phase 1, year 1. Evaluate insecticidal efficacy of cold-temperature (< 50 F) “Horn” or “Vaporphos” phosphine (100% purity) and warm-temperature (< 70 F) “Ecofume” phosphine (98:2%, carbon dioxide to phosphine mixture), and index relative to methyl bromide and sulfuryl fluoride at laboratory and pilot scales. Couple with residue analysis.

Phase 2, year 2. Engineer phosphine fumigations to be efficacious on the shortest timescale possible through the integration of physical (e.g., vacuum) and chemical approaches, such as developibng fumigant mixtures with other gases. Graduate toward commercial scales and scenarios used by the walnut industry for fumigation; included ~5,000 specimens of the most phosphine-tolerant life stage of dried fruit beetle, navel orangeworm, codling moth, red flour beetle, and warehouse beetle.

Phase 3, year 3. Apply what is learned from Phase 1 & 2 and tailor to logistics of commercial walnut harvest and distribution. Disseminate results of this study through local and annual meetings of the California Dried fruit and nut association.


3.Progress Report:

This Reimbursable Cooperative Agreement was established to support Objective 1 of the in-house project, which examines methyl bromide alternatives for postharvest applications. The goal of this research is to engineer phosphine fumigations to be efficacious on the shortest time scale possible through the integration of physical (e.g., vacuum) and chemical approaches, such as the use of other gases. Exposure to physiologically active gases, including nitrous oxide, before application of phosphine has reduced exposures time required to control the most phosphine-tolerant life stage of key insect pests, such as dried fruit beetle, red flour beetle, navel orangeworm, and warehouse beetle. Research continues to provide technical basis for interaction between the United Nations Environmental Programme - Methyl Bromide Technical Options Committee, United States Environmental Protection Agency, and the California Walnut Board as related to requests for methyl bromide Critical Use Exemptions.


Last Modified: 4/25/2014
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