Rose rust

Rose rust is a disease affecting the rose shrub caused by a number of fungi (such as Phragmidium tuberculatum). The spores of the rose rust fungi infect the leaves of the shrub during the beginning of summer, resulting in the appearance of orange pustules. Towards the end of summer, the orange pustules are superseded by black pustules, which contain overwintering spores.

Rose rust often causes the death of a rose shrub, with severe infections resulting in a weakening of the plant (and, in serious cases, death) due to premature defoliation.

Symptoms

• On stems: In spring, distorted young green stems, with large pustules of bright orange dusty spores.
• On leaves: Yellow spots on the upper surfaces, corresponding to pustules of dusty orange spores on the lower surface. In late summer, the orange pustules turn black. Infected leaves may fall early.

Treatment

Rose rust can be treated by pruning out spring infections as soon as they emerge and removing fallen leaves promptly during autumn. If infections are persistently troublesome, it may be that the cultivar concerned is unusually susceptible, and it may be necessary to replace it.

Further reading

• Royal Horticultural Society, entry on rose rust.

References

• "Rose rust". rhs.org.uk 'advicesearch' function. Royal Horticultural Society. http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=269. Retrieved 2009-12-11.