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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

2012 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 (MB) alternatives for postharvest applications. Research activity has progressed as planned in accordance with the diagnostic performance measures and corresponding time line as outlined in the original FY2011 proposal for Objective 1 (year 1, phase 1), We evaluated insecticidal efficacy of cold-temperature (< 50 F) “Horn” or “Vaporphos” phosphine (100% PH3), warm-temperature (< 70 F) “Ecofume” (98:2%, CO2:PH3) phosphine, and indexed them both relative to MB and sulfuryl fluoride (SF) at laboratory and pilot scale. Dose-mortality relationships for all fumigants have been established for all life stages of dried fruit beetle, red flour beetle, indianmeal moth, and navel orangeworm. Consistent with previous work in our lab, the egg and pupae life stages of each species are generally the most-fumigant tolerant. This research continues to provide technical basis for interaction between United States Environmental Protection Agency, Cytec - the registrant of Vaporphos, and the California Walnut Board as related to a label amendment that is the most strategic from the perspective of both insecticidal efficacy and existing infrastructural capacity of industry.


Last Modified: 7/30/2014
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