Here is an extract of the Guideline OEPP 1/268: Study of unintentional effects of plant protection products on fermentation processes and characteristics of wine.
The trial should form part of a series carried out in different regions with distinct environmental conditions. A minimum of six trials is required. It is recommended that the tests should be conducted for at least 2 years in viticultural regions which differ in climate and particularly in the sugar content of the grape at harvest.
At least 4 of the trials should be carried out in wine-growing zones, relevant to the country where the product is intended for registration.
Here is an example with several cases:
1 country targeted for registration: 6 trials minimum preferably split over 2 years,
2 countries targeted for registration: 8 trials minimum (= 4 per country), preferably split over 2 years
3 countries targeted for registration: 12 trials minimum (= 4 per country), preferably split over 2 years