Apple scab control with grapefruit seed extract: no alternative to chemical fungicides

Summary in the original language of the document

The growth inhibiting effect of four commercially available grapefruit seed extracts
on the causal organism of apple scab Venturia inaequalis was tested. Germination of
the conidia of Venturia inaequalis was pronouncedly inhibited by all tested extracts.
The commercial products were analyzed by high pressure liquid chromatography and
thin layer chromatography. All samples contained at least one preserving agent.
These substances were identified as either benzethonium chloride, benzalkonium
chloride, methyl parabene or propyl parabene. Freshly prepared extracts from seeds
of grapefruits (Citrus paradisi) did not inhibit the germination of Venturia inaequalis. It
was therefore concluded that the antifungal effect of grapefruit seed extracts is
caused by the added preservatives.