COURSE OF CHLORMEQUAT RESIDUE IN 'CONFERENCE' PEARS OVER A 9-YEAR PERIOD FOLLOWING ITS FINAL USE IN THE ORCHARD

Abstract

Chlormequat (CCC) was used for many years in the Netherlands as a chemical growth retardant to restrict vegetative growth and promote flower bud development in pears. After several years of annual applications, CCC residue levels in the fruits frequently exceeded the maximum residue limit (MRL) of 3.0 mg/kg. In 2001 the use of CCC in pears was banned and the MRL was reduced to 0.05 mg/kg. CCC is a very persistent chemical which seems to have accumulated in trees treated for many years with this growth retardant. Because of the expected carry over of these accumulated residues into fruits in the years following the last application of CCC, it was decided to decrease the MRL. In 2001 and 2002 a temporary MRL of 0.5 mg/kg was applied. From March 2003 until July 2006 the temporary MRL was reduced to 0.3 mg/kg. From August 2006 until July 2009 this was further reduced to 0.2 mg/kg. However, the final MRL will be reduced to 0.05 mg/kg within the shortest time possible. Pears sampled in years in which CCC was applied to the trees contained CCC residues that varied between 6.8 and 1.1 mg/kg, depending on the dosage and number of years of CCC application. During the first growing season without further CCC applications, the CCC residue of the fruits decreased on average by about 90%. During the following year without CCC the rates of decrease in CCC residues varied widely. In some trials a 60% decrease was noted in the second 'CCC free' year, while in other trials no further decrease was observed. In 2003 a further reduction was observed in most trees. Compared to 2002, the CCC levels had decreased by 6 to 80% and were all below the temporary MRL of 0.3 mg/kg. However, despite these decreases in CCC residue levels in trees grown for three to six years without any further CCC application, in 2003 the CCC residue in the fruits of most trees still exceeded the future MRL of 0.05 mg/kg. In 2006 only the fruits of one trial in Zeewolde still exceeded the MRL of 0.05 mg CCC/kg. In these trees which received their final CCC application in 1999, an average CCC level of 0.06 mg/kg was measured. Thus, even after 8 years of cultivation without CCC, pear trees which were amply treated with CCC in the past may produce fruits with a CCC residue level above the MRL of 0.05 mg/kg. Analysis of the wood of the trunks of these trees showed that this part of the trees still contained CCC levels up to 4.3 mg/kg. This CCC may have been partially transported into the fruits produced in 2007.