Puccinia coronata f. sp. avenae is the variation of the crown rust fungus which infects oat plants. Almost every growing region of oat has been affected by this pathogen at one point or another. During particularly bad epidemics, the worldwide crop yields have been reduced by up to 40%. One reason why Pca has such a prominent effect is that the conditions which favor oat production also favor the growth and inoculation of the rusts: Meaning that years in which the highest yields of crops are expected are the same years in which losses are the highest as well. Pca urediniospores germinate the best at temperature between 10–30 °C (50–86 °F) with germ-tube growth optimized at 20 °C (68 °F).