Large‐scale virulence tests using trees or saplings are expensive, time‐consuming and require a considerable amount of space. The suitability of using ‘ G olden D elicious’ apples as a rapid screen for identifying O phiostoma novo‐ulmi transformants with reduced virulence was thus evaluated. When a collection of O . novo‐ulmi field isolates belonging to subspecies novo‐ulmi or americana was inoculated to apples, members of subsp. novo‐ulmi induced, on average, larger necrotic lesions than subsp. americana isolates. The size of the lesions on apples was not correlated with mycelial growth rate of isolates on nutrient agar. Insertional mutants from O . novo‐ulmi subsp. novo‐ulmi isolate H 327 were inoculated to ‘ G olden D elicious’ apples and U lmus parvifolia × U . americana saplings in parallel experiments. Results clearly indicated that the O . novo‐ulmi transformants included several exhibiting significantly altered levels of virulence. Variability among replicates within a treatment was reduced in apple inoculation data compared to elm sapling data. Overall, the ‘ G olden D elicious’ apple assay was found to be an excellent means for rapidly assessing the virulence level of O . novo‐ulmi isolates.