Residue decline trials

OPPTS 860.1500, p. 16, indicates that 3-5 sampling points should be included in the decline trials. For applications close to the normal harvest time, the RAC may be harvested at selected intervals between the time of final application and a normal harvest or slightly delayed harvest. If the application is made long before the normal harvest, then representative plant tissues (including immature RAC) may need to be harvested in order to stretch the harvest period. A single composite sample is all that is required from each selected time point, but two or more samples may be harvested to reduce uncertainty about the actual amount of residue present at each sample time interval. These decline samples should be collected and treated the same as normal RAC samples. The samples should be frozen as soon as possible after collection. The instructions for decline sample collection and handling described in the protocol should be followed closely. 

Where a significant part of the consumable crop is present during the application, half of the trials reported should include data on the residue level present over time (residue decline studies). The number of decline trials may be reduced if it can be shown that the edible part of the crop is not affected or present at the time of application of the test item and no movement of the active ingredient or its metabolite occurs. 

An example of a supervised trial model in the Pesticide Agenda is shown in Figure 1, using bifenthrin at the highest recommended dosage on clementines. Application method, dosage, and equipment used are indicated in the information accompanying the decline curve. Five samples of 16 fruits each were collected at 0, 3, 7, 14, and 21 days after application and processed for residue analysis. 

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