Grapes (residues)

The contents of this guideline are, to some extent, covered by the Processing studies, Animal transfer studies, and Residue trials to obtain permanent maximum residue limits for crops guidelines. However, because the grape industry is so important to Australian trade, a separate guideline for residue trials in grapes is warranted.

This guideline addresses the generation of residue data for establishing maximum residue limits (MRLs) in grapes and the possible need for residue data in processed commodities such as wine and dried fruits and in by-products that may be consumed by stock. It does not deal with the effects of residues of agricultural chemicals on wine fermentation or with the issue of the potential for tainting the flavour of wine.

The APVMA currently requires the establishment of MRLs for the raw agricultural commodity grapes. While MRLs for wine are not normally set, it is assumed that the MRL for grapes also applies to the wine produced from those grapes.

1. Objectives of residue trials

You must conduct residue trials to establish an MRL for the active constituent in grapes. The residue data you present to the APVMA should reflect the maximum treatment regime allowed by the label derived from the maximum number of applications at the highest label rate to the vines at the shortest likely interval based on good agricultural practice.

Although there is no requirement to set MRLs for processed grape commodities in Australia, it is desirable from a trade perspective to produce some residue data. If there are no analytically detectable residues of active ingredient or relevant metabolites in the grapes at harvest, and there is adequate evidence to suggest that no concentration of residues will occur during processing, you will not need to determine residues in processed commodities. If residues (especially if greater than 0.1 milligram per kilogram) are found in grapes, processing studies are generally necessary. You should also consider the physicochemical properties of the active constituent.

Data from residue trials conducted overseas under an essentially similar use pattern as in Australia that support a finding in Australian trials of no detectable residues in grapes, and which indicate that residues will not concentrate, can be used to support the case that there is no need to conduct processing studies in Australia.

2. Conducting residue trials on grapes

It is not possible to specify the exact number of trials required but, in general, approximately four to six studies are needed to gain a representative picture of residues that could result in different areas across Australia. This will allow the setting of an MRL with confidence. The residue trials should reflect the use pattern specified on the label. Factors to consider are climate, canopy variation, number and frequency of applications, presence or absence of wetting agent, different varieties, berry size differences, berry arrangement and time of maturation. Variety and wine style influence the maximum treatment regime.

For trade considerations, you should obtain data on the time taken for the residue to decline to the limit of quantitation. A reverse decline residue study may be a suitable technique. In a reverse decline study, the product is applied to neighbouring plots at intervals corresponding to the possible treatment period before harvesting, and samples are taken from all the plots at the same time (harvesting). Two of the trials should follow the decline of residues.

You can use data from overseas trials to support data from local trials if the use patterns are comparable.

Since the variations in residue levels between replicates at individual sites are small compared with those between sites, it is usually not necessary to replicate treatments at more than one site. Studies with only one sampling (for example harvest) require at least two subsamples from each half of the plots. The samples taken should be analysed separately.

3. Sampling

From several of the trials, samples of fresh grapes should be taken at intervals to provide data to indicate the decline of residues. Refer to the Withholding periods guideline for more information.

You should take enough grapes so that you have an adequate amount to use in processing studies.

4. Volume of spray to be applied

For a pesticide spray to be efficacious, a certain amount of chemical must be applied evenly over the vines. The volume of spray depends on the nature of the vines, the spray application machinery and the way it is set up. Spray volumes between 300 and 1500 litres per hectare are commonly used.

The rate of use for a product is usually expressed as an amount per 100 litres, which allows flexibility to accommodate vines of different size and canopy density.

Residue trials are usually conducted using handheld spray equipment applying dilute spray mixtures. Dilute (sometimes called high-volume) spraying refers to the application of a spray volume to the point of run-off or drip. It is generally agreed that this leads to the highest residues, and these data are used to set MRLs.

5. Processing studies

Processing studies are used to support a proposal for a raw commodity MRL. Commodities that may need to be addressed are wine ready for bottling and dried fruit. Consideration may also be given to juice and marc.

Refer to the Processing studies guideline for guidance.

5.1. Wine

You should conduct trials to cover both white and red varieties and include skins when appropriate.

Use of overseas processing studies may be able to be used in lieu of Australian processing studies. You must specify the wine-making method used and whether or not a fining agent was present.

Fining agents such as bentonite, carbon or protein are sometimes used during wine production to remove particular taints. You must avoid using these agents when making wines for residue trials because they adsorb some pesticides.

5.2. Dried fruits

The effect of any treatment such as an alkaline or vegetable oil (spray or dip) that facilitates the drying process needs to be determined. The methods of processing should be clearly stated.

Overseas processing studies may be submitted in lieu of Australian studies provided the issues in the preceding paragraph are satisfied.

If residues concentrate in dried fruit during the drying process, you may need to propose a separate MRL for dried fruit.

5.3. By-products used for animal feeds

By-products from processing grapes are sometimes fed to stock. Bunch stems and marc are only occasionally used as an animal feed. If residues are likely to occur in animal tissues or milk as a result of feeding by-products of processing, you should propose appropriate MRLs for the meats and milks. Refer to the Animal transfer studies guideline for more information.

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