Whether and in which amounts residues are to be found in crops depends on the degradation rate of the active substance and the time interval between the last application and the harvesting of the crop.
The quantity of residues depends on the following factors:
- Type of application: treatments directly onto the crop in normal circumstances lead to higher amounts of residue than if seeds are treated prior to sowing for example
- Application amount: the larger the amount of active ingredient applied to the area, the higher the amount of residue tends to be in the harvested crop
- Number of applications and the time between applications
- Timing of the application: usually, the earlier the treatment is applied in the crop growing season the smaller the amount of residue
- Whether application is in a greenhouse or open air: because the influence of weather is usually lacking in the case of application in greenhouses (e.g. rainfall) any such application is to be viewed more critically from the point of view of residue assessment than those in the open air
- The period of time between application of the pesticide and the harvest (waiting period): as a rule, pesticide residues degrade over time
- Degradation properties of the active substance: i.e. how quickly a substance is broken down and into which by-products
- The active substance’s physical-chemical qualities: in this connection it is important whether a substance is transported via the vascular tissue system of the plants into the edible portions of the plant.