What is rose rust?

Rose rust is a disease caused by the parasitic fungus Phragmidium tuberculatum and some other closely related species. It is specific to roses, and appears in spring and persists until the leaves fall.

Susceptibility to rust varies widely among rose cultivars, and most modern roses should be resistant to rust.

Rose rust is the least serious of the common rose diseases; black spot and rose powdery mildew are far more prevalent.

Symptoms

You may see the following 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

Control

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Non-chemical control

• Prune out spring infections as soon as they are detected, to prevent the spread of spring spores
• Collect and destroy fallen leaves in autumn to reduce the number of overwintering resting spores
• If infections are persistently troublesome, it may be that the cultivar concerned is unusually susceptible, so consider replacing it with a different one (but be aware of potential problems from replant disease if another rose is planted in  exactly the same spot)

Chemical control

The fungicides tebuconazole (Provanto Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Provanto Fungus Fighter Plus, Toprose Fungus Control & Protect), and triticonazole (Fungus Clear Ultra) are labelled for the control of rose rust.

The following products contain a combination of both insecticide and fungicide, enabling the control of both insect pests and disease: myclobutanil containing cypermethrin (Resolva Rose 3 in 1, Rose Shield Bug & Fungus Killer, Roseclear Ultra Gun 2, Rosegarde) and triticonazole containing acetamiprid (Roseclear Ultra, Roseclear Ultra Gun).When a proprietary product contains an insecticide as well as a fungicide it would be preferable to use an alternative product if pests are not a problem on the plants treated.

Inclusion of a product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: storing and disposing safely

Biology

The fungus causing rose rust is, like all rusts, a biotroph: it infects the host tissues for extended periods without killing them, feeding from the living cells. Rusts are not able to feed from dead plant material, so must either alternate with a different, perennial host, or produce a resting spore to pass the dormant season.

Phragmidium tuberculatum and several other very similar rust species that infect roses do not have an alternate host; that is, they only attack roses and pass the winter as resting spores.

The first formed spores (spring spores) infect young stems, causing distortion and the production of bright orange pustules. Spores from these pustules in turn infect the leaves to produce dusty orange spores (summer spores) that are spread by wind and initiate further infections. Infection is favoured by prolonged periods of leaf wetness. In late summer, the pustules producing summer spores switch over to producing the dark, tough resting spores. These resting spores can survive the winter, on fallen leaves or often adhering to stems or trellises.

Infections may be severe enough to cause serious damage, but this is relatively rare and most infections are light enough not to require control.