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Final report
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Acetaldehyde and ethyl formate were investigated as possible fumigants for postharvest disinfestation of strawberry fruit. Target pests were western flower thrips and two-spotted spider mites. Strawberry fruit and target pests were exposed to acetaldehyde and ethyl formate at various concentrations and exposure times. Acetaldehyde was also combined with high carbon dioxide concentrations to test the possible synergistic effect of a controlled atmosphere. After treatment, strawberry fruit were evaluated for quality, and juice volatile content was analyzed. The mean mortality was determined for target pests. Results for quality assessments for fruit treated with acetaldehyde and ethyl formate were similar. Calyx damage increased with increasing concentration of fumigant. There were little to no effects on other quality parameters such as firmness and color. A series of experiments with repeated exposure to low concentrations of the fumigants revealed that fruit tolerance was higher for this type of treatment than for exposure to a single, high concentration of fumigant. Analysis of volatiles in strawberry juice after treatment with acetaldehyde revealed an increase in acetaldehyde, ethanol, and ethyl acetate. Over time these volatiles decreased to concentrations similar to those of the control in fruit stored at 20ºC, but remained elevated in fruit stored at 0ºC, even after four days. Western flower thrips were more susceptible to both acetaldehyde and ethyl formate than two-spotted spider mite. Western flower thrips responded similarly to repeated exposure to low concentrations of fumigant or a single high concentration. Two-spotted spider mites required exposure to a high concentration of fumigant for significant mortality to occur. Our results indicate that, while acetaldehyde and ethyl formate are toxic to western flower thrips and two-spotted spider mite, concentrations necessary for complete control are generally above those tolerated by strawberry fruit.
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