Carry-over effects of CCC-applications in pear orchards

Chlormequat (CCC) has been 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 transiently decrease the MRL. In 2001 and 2002 a temporary MRL of 0.5 mg/kg was in force. In 2003 a temporary MRL of 0.3 mg/kg came into force which will expire in June 2006. CCC-residue levels in pears, sampled in the final year of CCC application, varied between 6.8 and 1.1 mg/kg, depending on the dosage and number of years of CCC-treatment. 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 strongly. In some trials a 60% decrease was noted in the second 'CCC-free' year, while in other trials a much lower or 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. Only the residue levels of the ‘Doyenné du Comice’ trees planted in 1997 and treated with CCC during 1998-2000 were below 0.05 mg CCC/kg. In 2004 only the fruits of one trial 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 0.12 mg/kg was measured. In conclusion, the data demonstrate that for trees previously treated with CCC at recommended or lower rates, at least six seasons without CCC-application are needed to reach the MRL of 0.05 mg/kg