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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Commodity Protection and Quality Research » Research » Publications at this Location » Publication #285964
Title: High Temperature CO2 Treatments for Inshell Walnuts

Author
item PRASANTHA, ROHITHA - University Of Peradeniya
item Obenland, David - Dave
item Walse, Spencer
item Johnson, Judy

Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 9/10/2012
Publication Date: 11/6/2012
Citation: Prasantha, R., Obenland, D.M., Walse, S.S., Johnson, J.A. 2012. High Temperature CO2 Treatments for Inshell Walnuts. International Conference on Methyl Bromide Alternatives and Emissions Reductions, November 6-8, 2012, San Diego, California. 37:1-4.

Interpretive Summary: California walnut processors normally fumigate inshell nuts shortly after drying to disinfest the product of field pests such as navel orangeworm or codling moth. Environmental restrictions on those fumigants currently used require that non-chemical alternatives be considered. Earlier work found that 98% CO2 at 43C for 7.3 hours should be an effective phytosanitary treatment for these insects, as the treatment was estimated to provide quarantine level mortality for diapausing codling moth larvae, the most tolerant insect and life stage. This paper evaluates the treatment as a potential alternative to fumigation, using a laboratory CATTS unit (Controlled Atmosphere/Temperature Treatment System) to apply the treatment to inshell walnuts artificially infested with laboratory-reared diapausing codling moth. Ancillary studies showed that walnut moisture levels were reduced from about 8.4% to about 6.5 and 5.5% after 7 hours in hot forced air ovens kept at 38 and 43C, respectively. This suggests that some humidity control in the treatment may be necessary to prevent excessive drying of the product. Additional studies examined the amount of CO2 absorbed by walnuts under high CO2 conditions. Walnuts absorbed relatively high levels (4-5%) of CO2 within the first 8 h of the treatment, probably due to the high oil content in walnuts, and indicates that care must be taken to maintain the CO2 levels in commercial applications of this method to walnuts.

Technical Abstract: Environmental restrictions on those fumigants currently used to disinfest inshell walnuts of field pests require that non-chemical alternatives be considered. Earlier work found that 98% CO2 at 43C for 7.3 hours should be an effective phytosanitary treatment for these insects, as it is the estimated probit 9 upper 95% confidence limit for the most tolerant stage (diapausing codling moth larvae). This paper evaluates the treatment as a potential alternative to fumigation, using a laboratory CATTS unit (Controlled Atmosphere/Temperature Treatment System) to apply the treatment to inshell walnuts artificially infested with laboratory-reared diapausing codling moth. Ancillary studies showed that walnut moisture levels were reduced from about 8.4% to about 6.5 and 5.5% after 7 hours in hot forced air ovens kept at 38 and 43C, respectively. This suggests that some humidity control in the treatment may be necessary to prevent excessive drying of the product. Additional studies examined the amount of CO2 absorbed by walnuts under high CO2 conditions. Walnuts absorbed relatively high levels (4-5%) of CO2 within the first 8 h of the treatment, probably due to the high oil content in walnuts, and indicates that care must be taken to maintain the CO2 levels in commercial applications of this method to walnuts.