Pesticide Registration Toolkit

Comparison of GAPs

Comparison of Good Agricultural Practices (GAPs) – adopted national MRL

Principle

The exact pesticide use details are key input parameters for dietary risk assessment as well as for the establishment of MRLs. These are referred to as the Good Agricultural Practice (GAP) of the pesticide.
GAP in the use of pesticides includes the officially recommended or nationally authorized uses of pesticides under actual conditions necessary for effective and reliable pest control. It encompasses a range of levels of pesticide applications up to the highest authorized use, applied in a manner which leaves a residue which is the smallest amount practicable.
To establish an MRL, the regulator will identify the likely scenarios which may lead to the highest residues in food or feed, which is often referred to as the critical GAP or maximum GAP . Dietary risk assessment is done for the critical GAP.
The starting point of this assessment is that a national MRL has already been adopted for a given pesticide and commodity (-group), with an associated GAP. If a new application for registration is made for the same pesticide active ingredient and the same commodity or commodity group, the registrar should assess whether the GAP of the new application is more or less “critical” than the GAP on which the MRL was originally based. 

Applicability

Comparison of GAPs can be done if the two cases to be compared concern the same pesticide active ingredient and the same commodity or commodity group.
It is assumed that the dietary risk assessment resulting from the GAP on which the MRL has been based was evaluated and considered acceptable.

Data requirements

The following data are needed to compare GAPs for an already adopted MRL.
  1. MRL adopted for the pesticide and crop (-group).
  2. GAP table (or information) for the use on which the MRL was originally based.
  3. GAP table (or information) of the new application for registration.
The key parameters in a GAP table are:
  • Crop (according to the Codex classification of food and animal feeds [Standard CAC/MISC 4]) and/or use situation
  • Product name
  • Type of use (e.g. field, greenhouse, indoor)
  • Pest or group of pests
  • Formulation type (according to CropLife International formulation codes) & concentration
  • Application method (e.g. high volume spraying, granule drilling, low volume application) and kind of application (e.g. broadcast, aerial spraying, between plants – indicate type of equipment)
  • Minimum and maximum number of applications (per year or per season) & minimum application interval.
  • Minimum and maximum application rate per treatment (as kg a.i./hectolitre & litres of water/ha & kg a.i./ha)
  • Minimum pre-harvest interval (PHI)
An example of a GAP table, as recommended by OECD, can be found here. icon A07-01-01-#1 – GAP table example

Assessments

The parameters in the GAP tables are compared, and it is assessed whether the new GAP is similar, more, or less critical than the GAP on which the MRL was based.
From the point of view of residue levels on agricultural commodities, GAP parameters are considered similar in the following cases.
  • Application rate. Application rates may be considered similar if they do not deviate more than 25%
  • Pre-harvest interval. Pre-harvest intervals may be considered similar if they do not deviate more than 25%
  • Number of treatments. When a large number of applications are made in trials (more than 5 or 6) earlier treatments should not be considered to contribute greatly to the final residue unless the compound is persistent or the treatments are made with unusually short intervals. If the above three parameters deviate in the same direction simultaneously, the resulting difference in GAP is not considered similar anymore.
  • Formulation type. In many situations different formulations would cause no more variation than other factors, and data derived with different formulations would be considered comparable. The most common formulation types which are diluted in water prior to application, such as EC, WP, water dispersible granules (WG), suspension concentrates (SC) and soluble concentrates (SL) can be considered similar.
In establishing comparability of residue trials data in which more than one of the first three parameters, i.e. application rate, number of treatments or PHI, deviate from the reference, consideration should be given to the combination effect on the residue value which may lead to an underestimation or overestimation of the residue level. Generally, trials should not be used where two critical parameters of GAP deviate. For example, a trial result should not be considered similar if both the application rate is lower (e.g. 0.75 kg/ha in the local situation; 1 kg ai/ha in the reference country) and the PHI is longer (perhaps 18 days in the local situation, 14 days in the reference), as these parameters could combine to underestimate the residue.
More guidance on similarity of GAPs in the JMPR Manual, in particular Chapter 6.2.

Interpretation of the outcome

If, overall,  the GAP of the new application for registration can be considered similar or less critical than the GAP on which the MRL has been based, the new application for registration is unlikely to exceed the established MRL.
If, on the other hand, the new GAP is more critical, then dietary risks may be greater than originally estimated for the established MRL. In such a case, a dietary risk assessment  should be conducted.
Note: If the new GAP is more critical than the one on which the MRL was based, and if the dietary risk assessment shows that the risk is acceptable for this new GAP, the MRL may need to be revised. See the section on comprehensive residue evaluation and MRL establishment.