Rose rust is a common problem in roses. It is caused by two species of fungi: Fusarium oxysporum f. sp. cubense (rust) and Rhizoctonia solani var. rubra (brown spot). Both species are found worldwide, but they have been most abundant in warm climates where temperatures often exceed 80°F (27°C), such as North America, Europe, Australia and New Zealand. They are not native to these areas, but have spread there from other parts of the world.

Rust usually appears as small brown spots or patches on the petals and leaves of roses. It may appear at any time during the growing season, but it tends to occur earlier in warmer regions than cooler ones. When it occurs, rust usually develops within a few days after frost and lasts several weeks before dying off.

It does not affect roses grown indoors. However, rust outbreaks do cause problems when they occur in gardens outside.

The fungus causes rust on roses because it eats away at the plant’s vascular tissue, causing the leaf to die and eventually kill the flower. There are many different types of rusts, which differ in their appearance and how quickly they develop. The most common type is often known as orange rust because it causes the damaged parts of the plant to turn a bright orange colour.

Other types include blue rust, which colours the plant dark blue, yellow rust which turns the plant light yellow and olive rust, which makes the plant an olive colour.

Rose rust is often confused with a similar disease called black spot. Black spot is caused by a separate fungus known as Puccinia. It is less common and does not turn the plant an unusual colour, but it can cause even more damage than rust.

Fungicides will not stop black spot from growing, so it is necessary to remove and destroy all infected parts of the rose to get rid of it.

The fungus that causes rust on roses is wind-born. It spreads from plant to plant until it finds one which has some kind of weakness. Roses with a weakened immune system are the most susceptible to infection.

This could be caused by a number of different things.

Roses do not have perfect flowers and most people realize that the reason for this is to encourage pollination and seed spreading. Some diseases and pests can weaken a rose’s immune system, making it far more susceptible to diseases like rust and black spot. Among the most common are aphids, spider mites, leaf miners, mealy bugs and caterpillars.

These insects specifically target roses and tend to thrive in the same conditions that rust prefers, so a rose that has any of these problems is likely to get rust as well. Fortunately, they are easy to get rid of and do not do extensive damage.

The second most common cause of a weakened immune system is bad care. Roses require a lot of TLC and if it is neglected, their immune systems can be damaged. The most common causes of this are water and nutrients.

It is vitally important that roses get as much water as they need, but not too much. Too much water can cause the roots of the plant to rot, which makes it far more susceptible to disease. A good rule of thumb is to water it when you water the rest of your garden and always wait until the top 1 inch (2.5 cm) of soil has dried out before watering again.

Nutrients are also important. Roses require lots of nutrients to produce such beautiful and strong flowers and if they don’t get enough, their immune system suffers. A good fertilizer will provide all the nutrients a rose needs and will keep its immune system strong.

Rose Rust Disease – Treating Rust On Roses - Picture

The third most common cause of a weakened rose’s immune system is the dark colours of its petals. Dark colours attract heat and too much heat causes roses to release the excess as a defence mechanism. The chemical released in this situation, known as achromein, is also responsible for the roses’ strong scent.

Unfortunately, it also weakens the rose’s immune system, leaving it more susceptible to pests and diseases. Roses with light colours do not suffer this problem.

Rose rust doesn’t directly kill roses, but if left unchecked it will slowly destroy them. It is always best to nip the disease in the bud as quickly as possible and treat your rose against it before any damage is done.

Sources & references used in this article:

Efficacy of hexaconazole for the control of white rust on chrysanthemum and powdery mildew on roses by CH Lam, TK Lim – International Journal of Pest Management, 1993 – Taylor & Francis

Developments in breeding for horizontal and vertical fungus resistance in roses by DP De Vries, LAM Dubois – … , Strategies for New Ornamentals-Part I 552, 2001 – actahort.org

Screening of fungal diseases in offspring from crosses between Rosa sections Caninae and Cinnamomeae by M Uggla, BU Carlson-Nilsson – Scientia horticulturae, 2005 – Elsevier

Downy mildew: a serious disease threat to rose health worldwide by AG Bailey – Mycologist, 1988 – Elsevier

Evaluation of Some Fungicides Against Rust and Black Spot in Rosa damascena cv. trigintipetala by C Salgado-Salazar, N Shiskoff, M Daughtrey… – … disease, 2018 – Am Phytopath Society

Controlling powdery mildew in field roses by A Margina, V Zheljazkov – Journal of Essential Oil Research, 1995 – Taylor & Francis

The effect of Phragmidium mucronatum on rose understocks and maiden bush roses by A Paulus, J Nelson, O Harvey – California Agriculture, 1977 – calag.ucanr.edu

Effectiveness of antifungal compounds against rose powdery mildew (Sphaerotheca pannosa var. rosae) in glasshouses by RC Shattock, MHR BHATTI – Plant Pathology, 1983 – Wiley Online Library

Rose diseases: Their causes and control by C Pasini, F D’Aquila, P Curir, ML Gullino – Crop Protection, 1997 – Elsevier

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