Field inoculation experiments were performed during 2015–2017, in south-eastern part of Poland. The pathogenicity of F. crookwellense was estimated based on the kernels yield reduction of 10 selected oat genotypes. Panicles of oat were inoculated with conidial suspension of F. crookwellense strain No. 72 which caused a reduction in kernels yield by 28.54% and kernels number per panicle by 28.07%, compared to the control. The lowest yield reduction, as a result of the panicle inoculation with F. crookwellense, was found in the case of the cultivar ‘Pablo’ (18.73%), while the highest in the case of breeding line POB 961-1344/13 (36.4%) and cv. ‘Kozak’ (34.3%). Statistically the highest average yield reduction was observed in year 2016, when a higher amount of rainfall, especially in July (just after inoculation) and higher temperature, compared to the long-term standard, were observed. During the period between inoculation and harvest, F. crookwellense was able to produce nivalenol, fusarenone X and zearalenone in oat kernels at the average level of 0.065 mg∙kg-1, 0.026 mg∙kg-1 and 0.015 mg∙kg-1 respectively.