Crops: post-harvest applications except fumigants and grain protectants (residues)

Post-harvest treatments are applied to raw commodities and processed foods and feeds to control a range of insects and disease organisms that could otherwise adversely affect the produce in storage before consumption. They can be applied by various means including sprays, dips, drenches and brush applicators. For fresh fruit, a wax may also be applied and sometimes various detergents and rinse processes are used.

This guideline does not cover the use of fumigants or grain protectants. For fumigants, refer to the fumigants guideline. Grain protectants will be the subject of a future guideline.

1. Objective of residue studies for post-harvest uses

Both raw agricultural commodities and processed food and foodstuffs can be subjected to post-harvest treatment. The objective of post-harvest residue studies is to determine the appropriate maximum residue limit based on the maximum use of the product according to the label directions.

2. Conducting residue trials on post-harvest treatments

Data should reflect the recommended use pattern and should result from treatments using commercial machinery. Trials should be carried out on the formulation that will be sold.

Treatments with the recommended concentration and with 1.5 to 2 times the recommended concentration of the treatment chemical should be included. Details of maintenance of the concentration of the solution in the dip or spray should be given.

Any other treatments such as the application of waxes, use of detergents and rinsing processes should be provided. Samples should be taken after all processes are completed.

If the chemical is also registered for use on the crop before harvest that use should precede the post-harvest treatment to provide for the maximum residue levels should these residues be accumulative.

Residues normally break down in storage and therefore a decline study is necessary. The handling and storage conditions after treatment should be described.

3. Fate of residues during storage, processing and cooking

Decline of residues

Because it is normally impracticable to impose a withholding period for a post-harvest treatment, you should provide any available information about the effect of storage, processing or cooking on the residues. Details should be provided on the degradation products or metabolites that may be produced and that are likely to be present when food is consumed. Information should be provided on the level of residues in food as consumed.

Processing studies

Further details on processing studies are given in the processing studies guideline.

Animal transfer studies

Animal transfer studies are required when the treated raw commodity or treated processed commodity contains greater than 0.1 milligram per kilogram of residue and is fed to livestock and poultry.

Further details are given in the animal transfer studies guideline.

4. Proposals for maximum residue limits and withholding periods

For products that are proposed for post-harvest use, good agricultural practice generally dictates that withholding periods will not be practicable, except in exceptional circumstances. Therefore, the extent of data required to support a post-harvest use will normally be greater than that required for pre-harvest uses.

The maximum residue limit should be recommended at a level to cover residues resulting from normal practices.

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