Evaluation of grapefruit seed extract as natural fungicide to control apple scab in organic apple growing

C-pro, an experimental fungicide based on grapefruit seed extract was compared to copper oxychloride for the control of apple scab in a field trial. Efficacy and possible phytotoxic effects where accessed. The C-pro formulation was analysed for possible chemical additives by HPTLC. C-pro proved tot be more effective in controlling apple scab then the standard rate of 300 gram copper oxychloride per ha, and gave a better leaf quality and less fruit skin russeting then the standard program of copper oxychloride. However C-pro contained 6.6 % of the synthetic preservation agent benzethonium chloride what excludes C-pro from use in organic agriculture. There is a growing interest in grapefruit seed extract products as well as in other plant extracts as potential crop protection materials. To prevent disappointments and waist of resources it is necessary to analyse these materials on possible chemical additives before taking them into efficacy trials.