These named species are all very similar plants (and to make individual identification more difficult hybrids between Scotch and Illyrian Thistles are common). They produce seed in large quantities (up to 20 000 per plant in Scotch Thistle) and seed is stored in the soil for many years when buried and will germinate when a paddock is cultivated. Infestations degrade pastures and crops and contaminate hay and seed crops. They are often difficult to control using herbicides because of the woolliness of the leaves. Goats are of some assistance in grazing the flowering plants. Integrated weed management is vital for effective control: the best defense against invasion on agricultural lands is maintaining healthy perennial pasture with good ground cover at all times to prevent seedling establishment.