Residues of plant protection products (PPPs) are inevitably present in or on food, even when they are applied in line with good agricultural practice. The upper limit of residue permitted on food or feed is the ‘maximum residue level’ (MRL), which, in Europe, is legislated by the European Commission based on scientific advice from the (EFSA).
MRLs are measured via crop residue field trials, which replicate the real-life agricultural conditions under which a PPP would be used. It sounds a simple enough procedure, but what studies are commonly used and what are the secrets to success?
Field trials for crop residue analysis
The term field trial covers trials conducted on crops grown under cover or in open fields. There are essentially two main types of field trial:
- Decline trials, in which samples of the crop – or ‘raw agricultural commodity’ – are collected after application of the PPP and at specific times before harvest to see how the level of residue decreases over time
- Harvest trials, which assess the residue remaining in the crop after it is harvested.
These trials are used to both support initial registration of the PPP substance and re-register the substance when, for example, the range of crops it is to be used on is extended, such as when the registration of a pesticide licensed for use on apples is extended for use on other fruit crops like peaches.
Seven top tips for ensuring field trial success
The success of field trials can be enhanced by following some simple rules:
- Site the trials to maximize diversity: select different countries and locations for your field trials to reflect the variations that occur in climate and farming practice throughout Europe. As a general rule, a minimum of eight trials per major crop are required, and if the registration is pan-European, then these eight trials must be done in both northern and southern Europe.
- Mimic farming practices used in real life: use the kind of equipment which would simulate that used commercially for PPP applications and usual farming practices.
- Ensure the crop is healthy at baseline and without potential problems: consider the location of the trial and try to cite the trial areas away from field margins where there may be interference from a PPP applied to neighboring fields.
- Optimize sample handling: ensure that samples are collected and frozen as soon as possible after sampling and at least within six hours. Maintain frozen conditions until samples are returned to the laboratory for analysis and ensure the timing of the analysis reflects the stability of the sample.
- Have a team with diverse expertise: having a team with expertise in agriculture and analytics ensures the studies are designed to account for growing seasons, geographical diversity and any conditions specific for optimal sampling and chemical analysis.
- Plan ahead: an average study takes approximately ten months from application of the product to reporting; add to this the need to have a crop ready for application and you can see the importance of forward planning.
- Be flexible: by having access to a wide geographic spread of field capacity which you can flex, you can easily run studies in northern and southern Europe as required and under very diverse conditions.
About the author
Javier Bartolomé, Test Facility Manager and Study Director at Covance has a degree in Agronomy and joined Covance in 1999. The field facility in Valencia has held GLP compliance for over ten years and Javier has been involved in the design of the study plans and field activities for all study types in the Covance portfolio.