Spray deposits of crop protection products on plants – the potential exposure of non-target arthropods

Spray deposits of plant protection products on cultivated plants present a potential hazard to non-target arthropods. This hazard is considered in the risk assessment procedure when such products are registered. The results of deposit measurements in the laboratory and field, including mean spray deposits on plant surfaces, their variability and their relation to the delivered dose are presented. Initial deposits expressed as ng/cm2 plant surface were measured on individual leaves of various plant species using a fluorescent tracer. The results show that the mean deposit is plant-specific but with a high degree of variability. Mean deposits on field-grown cereals were 3, 9 (growth stage BBCH 10) and 4, 7–14 ng/cm2 (growth stage BBCH 29–63) at a delivered dose rate of 20 g sodium flourescein (SF) per ha. This is equivalent to 200 ng tracer per cm2 ground area. On apple leaves, mean deposits varied between 18 and 50 ng/cm2 at a rate of 20 g tracer/10 000 m2 fruitwall. Coefficients of variation of leaf deposits ranged between 30% and 90%. In addition to the leaf-to-leaf variability, there was a notable variation of the deposit on individual leaves themselves as shown for wheat. Data from field measurements were supported principally by data from tray-grown plants on a laboratory spray track which gives information on targets positioned in a more or less two-dimensional system.