P. oxalicum is known as plant pathogen, mycotoxin producer and was suggested to be involved in the induction of champagne gushing. Early detection of the fungus enforces decision making in the wine industry as to how grapes will be further processed. A loop-mediated isothermal amplification (LAMP) assay for P. oxalicum was established with a detection limit of 100 pg genomic DNA per reaction. The assay was highly specific for P. oxalicum DNA. The assay was applied for the detection of the fungus on artificially infected grapes using surface washings as target for the LAMP reaction. Screening of grape samples from different European countries revealed the (rare) presence of P. oxalicum on grapes harvested in Italy and Portugal. We suggest the developed LAMP assay as a promising new tool for the rapid, robust, highly specific and sensitive as well as cost efficient detection of P. oxalicum on grapes used in the wine and champagne industry.