(1938) Phragmidium is a genus of rust fungus that typically infects plant species in the family Rosaceae.

[3] Phragmidium tuberculatum, also known as rose rust, is a parasitic fungus that feeds on living cells of a host plant.

[citation needed] The climate most favorable to rose rust is mild temperatures with high moisture.

[citation needed] In the spring, the very first spores, spermatogonia, arise out of the debris on the ground and infects the young stem, distorting them and producing orange pustules.

Eventually in late August, the urediniospores and sori become speckled with black fascicles and dark resting spores called teliospores.

[citation needed] Roses infected with species of Phragmidium will show a characteristic orange mass of spores and distorted growth at specific locations on the bush.

Non-chemical controls include pruning out the spring infections as soon as possible along with collecting and destroying fallen leaves to prevent overwintering.