Study of potatoes' sprout inhibitor treatments with chlorprophame.

Studies carried out in 1999 by the University of Ghent showed that 36% of potatoes' samples contained Chlorprophame (CIPC) residues and that 7.9% of them exceeded the maximal limit of residues (RML), fixed at 5 ppm. The heterogeneity of sprout inhibitor application would be one of the causes of over-dosage. However, this heterogeneity would also cause under-dosages leading to problems when controlling the sprouting in potatoes stored over 6 degrees C. This study aims at determining some technical causes of the heterogeneity of CIPC sprout inhibitor treatments when storing potatoes. The study concerns two treatment techniques: dusting and spraying. To draw up an inventory of mechanical treatments in Belgium, a survey has been conducted among 28 farmers throughout Belgium. 35 samples have been taken at random in the different storage rooms to analyse the content of CIPC residue. In order to do so, a method of analysis: the gas chromatography in capillary phase with detection by mass spectrophotometry, has been developed. Tests have been carried out by changing several parameters such as the material, the product or the place in the storage line, in order to assess the CIPC application techniques. The survey made it possible to analyse qualitatively, from the declarations of farmers, the causes of heterogeneity linked to treatment techniques. An almost systematically over-dosage of the CIPC quantity has been noticed. However, out of the 35 samples analysed, only 2 had residue contents higher than the RML. The comparative analysis of the quantities applied and the residues contained in the samples made it possible to quantify the heterogeneity of the applications depending on the techniques. The tests carried out show in a general way that mechanical dusting, even though having a less constant flowrate than sprayers, leads to less important variation of the residue between samples. In testing conditions, the heterogeneity of the antigerminative treatment decreases when applied by means of a mechanical duster. In practise, these results are distorted by topical applications of CIPC. The combination of this practise with a too high heterogeneity of the treatment are to be avoided in order to have a good preservation and meet the residues standards.