PlantNET NSW Flora Online says inflorescence of Cortaderia jubata is well exserted from basal leaves while inflorescence of C. selloana (common pampas grass) is usually barely exserted from the basal leaves. There are other distinguishing features particularly those of the flowers but this plant has old faded flowers and it would be hard to tell. On the basis of the long flower spike this could be C. jubata and should be removed. Why take the risk?