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

Abstract

Variation in pesticide residues in space and time has not been investigated systematically in spite of the large variability found at single scales (e.g. between trees or orchards). Information on variability at different scales will support the development of sampling methods and more reliable prediction of residues. Experiments were conducted to quantify the spatiotemporal variability in initial spray deposit on apple leaves and fruit using a substitute tracer (zinc EDTA chelate). Five hierarchical spatial scales were defined as (1) between orchards, (2) between plots within an orchard, (3) between trees within a plot, (4) between zones within a tree and (5) between leaves/fruit within a zone. Similarly, two temporal scales were defined as (1) between applications within a single year and (2) between years. The initial zinc concentration was approximately log-normally distributed; the variability in initial deposit concentration was greater on leaves than on fruit. The average initial zinc deposition was significantly greater in the top and outside zones than in the middle zones within individual trees. The most important scale for driving residue variability is the within-zone unit-to-unit variation, contributing to 71 and 49% of the observed variability for leaf and fruit samples respectively. Variability at other scales was related to the variation in the tree architecture. The results indicated that stratified sampling on the basis of within-tree zone structures, with the effort focused on within-zone sampling, should be used for the determination of pesticide residues.

Modelling non-systemic pesticide residues in fruits with initial deposit variability and weather effects

“…variation in initial deposit (Walklate et al 2003;Xu et al 2006), physical decay due to weather factors (Smith and MacHardy 1984) and growth dilution (Lakso et al 1995). The degradation of pesticide residues concentration due to the three processes has been approximately described by a first-order reaction model (Timme and Frehse 1980;Holland et al 1996).…”

Contamination of apple orchard soils and fruit trees with copper-based fungicides: sampling aspects

“…Additionally, the uptakes and accumulations of Cu in leaves or fruits are not only from the uptake of Cu from the soil but also from the deposit of Cu-containing fungicides (Özcan et al 2012). Many studies have shown that initial spray deposit and retention of pesticides are critically influenced by tree canopy structure (Travis et al 1987;Xu et al 2006;Rawn et al 2007). This variability would result in variation in differential interception of Cu deposit between zones among trees, leading to the significant observed zone-tree interactions.…”

“…3). The different enrichments of Cu in soils under different positions of the apple trees are apparently due to the different initial spray deposit of the different canopy compartments, which can result in different leaching effects through the drift, or dripping of excess sprays from leaf surfaces (Xu et al 2006;Rawn et al 2006).…”

“…Xu et al (2006), who quantified the spatiotemporal variability in initial spray deposit on leaves and fruit using a substitute tracer (zinc EDTA chelate), found that leaves and fruits in the top and outside zones received more Zn deposit than those in the inside zones. Additionally, the highest organophosphate residue levels were observed in apples harvested from the mid-height of the apple trees (Rawn et al 2006).…”

“…It is widely known that apple tree has a large canopy. Different metal spray deposit amounts have been found between the locations at the outside of the canopy and the locations near tree trunk (Xu et al 2006). However, most studies about the soil Cu accumulations in orchards are investigated by composite soil samples which are collected at random (Aoyama 1998;Li et al 2005), at a certain distance from tree trunk (such as 1 m, Wang et al 2009), or at the middle and the edge of orchards (Holb and Nagy 2009).…”