THE EFFECT OF SPRAY REGIMES ON CAPTAN RESIDUES IN APPLE
T LOCKE1, RA UMPELBY1, C KNIGHT2 and B CROZIER2
1ADAS Rosemaund, Preston Wynne, Hereford, HRI 3PG, UK;2CCFRA, Chipping Carnpden, Glos. GL55 6LD, UK
Background and Objectives
Pesticide residues in food are a major concern of government. The project reported upon here was undertaken on behalf of MAFF to determine the effect of spray volume on the residues occurring in apples at harvest of a range of pesticides con-unonly used in apple orchards. The results for the fungicide captan are dealt with in this paper.
Materials and methods
An orchard of cv. Cox's Orange Pippin was used for experimentation in 1995 and 1996. Plots were of 5 rows of trees. 44m in length, and each treatment was replicated 4 times in a randon-dsed block design. Sprays were applied from the end of flowering until harvest using a tractor-mounted air-assisted sprayer. The five treatments consisted of different water volumes to carry the pesticides. The volumes used were 1000, 500, 200 and 50 l ha-1, with two spray frequencies of the routine niildew and scab fungicide programme using 50 lf ha-1 via ULV nozzles. In 1995 the standard fungicide programme spray interval was 10 days, with one ULV programme at 5 days. In 1996 these were changed to 14 and 7 days respectively. Pesticide rates were used at manufacturer's recommendations for the water volume and spray interval. Where water volumes below the minimum recommendation were used the pesticide concentration was kept at that advised for the minimum water rate. Captan was applied for scab control in tank mix with myclobutanil throughout the season with extra preventative treatments for storage rot control, 4 days before harvest.
Fifty fruits were harvested from four different parts of the tree canopy: from branches (a) adjacent to the alleyway (b) in the centre of the tree (c) at the top of the tree and (d) where branches met along the tree row. The fruits were bulked for analysis. Analysis was carried out using an in-house UKAS accredited method in which the samples are extracted with acetone:methanol (50:50) and partitioned with petroleum spirit and dichloromethane. Clean-up of extracts by Gel Permeation Chromatography was followed by determination of captan residues by Gas Chromatography using Mass Spectrometric Detection .
Results and conclusions
The UK MRL for captan in apple fruit is 3 mg/kg. In 1995 levels detected in the bulk samples range from 0.1 to 5.36. In no case were levels above the MRL detected in apples from either of the 50l ha-I treatments, and none were found in samples from the top branches in any treatment. The general trend was for higher residue levels in the fruit picked from the peripheral branches, (a) and (d). Also, residues decreased with increasing water volumes from 200 to 1000 l ha-1, except in the centre of the tree where the highest residues were in fruit treated at 1000 l ha-1.
In 1996 residues were higher overall, in the range 0.75 to 17.11 mg/kg, approaching the Codex limit of 25 mg/kg.In a number of cases MRLs between 3 and 4 mg/kg were detected in the 50l ha-1 treatments. With the higher water volumes, mean levels over the MRL were found in all combinations of water volume and sampling position, apart from at the top of the tree where 500 or 200 l ha-1 had been used.
Of particular concern is the fact that residues of captan above the MRL were found in bulked samples of 50 fruit. Within this bulk, individual fruits are likely to have carried higher levels. It would seem that the dose rate and/or harvest interval currently recommended should be reviewed in the light of these findings.
1. Luke MA, Froberg JE, Doose GM, Masumoto, 1981. Journal of the Association of Official Analytical Chemists 64, 1187-1195.