Variability in initial spray deposit in apple trees in space and time

Area of Science:

• Agricultural Science
• Environmental Chemistry
• Pesticide Application Technology

Background:

• Systematic investigation of pesticide residue spatiotemporal variability is lacking.
• Variability at different scales is crucial for developing effective sampling strategies.
• Existing knowledge gaps hinder reliable residue prediction models.

Purpose of the Study:

• To quantify spatiotemporal variability of initial spray deposit on apple.
• To identify key scales influencing residue distribution on leaves and fruit.
• To inform the development of optimized pesticide residue sampling methods.

Main Methods:

• Utilized zinc EDTA chelate as a substitute tracer for spray deposit.
• Defined five hierarchical spatial scales (orchard to within-zone) and two temporal scales (within-year and between-year).
• Analyzed initial zinc concentration distribution across scales and sample types (leaves vs. fruit).

Main Results:

• Initial zinc concentration followed a log-normal distribution.
• Variability was higher for leaf samples than fruit samples.
• Within-zone unit-to-unit variation was the primary driver of residue variability (71% for leaves, 49% for fruit).

Conclusions:

• Stratified sampling focusing on within-tree zone structures is recommended for pesticide residue determination.
• Tree architecture significantly influences residue variability at larger scales.
• Optimized sampling strategies can improve the accuracy of pesticide residue assessment.