Abstract
Although potassium phosphite is not registered for organic fruit production in Europe, it has long been regarded as a potential alternative to sulphur-and copper-containing fungicides. In 2005/2006 a field trial was carried out to verify the presence of residues of phosphoric acid over time in apples after applications of potassium phosphite at different time-points. No residues were present on fruits if treatments were applied before flowering, whereas treatments after flowering, in the summer or in autumn resulted in comparable residue levels irrespective of the period of application. Residues were eveneven found in leaves and fruits of the following years, 2006 and 2007.