Pesticide use varies according to the crop, the climate, types of pest present and the numbers of these pests in a given year.

The conditions under which particular crops are grown can also affect the need for pesticides; for example, tomatoes grown under cover need no pesticides or fewer pesticides than those grown outside.

In addition, some pesticides, such as those used post-harvest are designed to stay on particular crops. In contrast, other pesticides break down so that no residues are left by the time the crop is harvested.

The monitoring programme in 2005 showed that 68% of the food samples did not contain detectable pesticide residues when they were tested for a range of pesticides likely to be found. These are overall results: the results for oranges showed 100% of samples containing residues, whereas no samples of swedes contained residues. The surveillance looks for pesticides most likely to be applied to a particular crop, plus non-approved pesticides that may have been used on the crop.