Rose problems: frequently asked questions

Roses seem to suffer from more than their fair share of problems. It is probably partly because this much-loved plant is so widely grown, often in formal rose borders or gardens, and any pest, disease or other problem is soon noticed. That said, some of the older varieties in particular can be very prone to foliar diseases.


Quick facts


Most common problems

  • Aphids

  • Rose black spot

  • Rose powdery mildew

  • Rose dieback

  • Rose leaf-rolling sawfly


Roots


My rose bush looks as though it is dying. I dug down to look at the roots, and found that many of them were soft and brown. What has happened?


Root decay in roses can be the result of an attack by a root disease. Honey fungus is quite common on soil-grown roses and plants grown in soil or containers can sometimes be affected by Phytophthora root rot.


Roses are suitable for growing in clay soils, but prolonged waterlogging can result in root rotting. Drainage problems in containers can also lead to waterlogging and root death.


Root death in container-grown plants can sometimes be the result of hard frosts – the roots can be given some protection by wrapping the container with bubble wrap.


I replanted my old rose border with new roses, but they have never thrived. On lifting a couple of the plants I found that they had hardly rooted out. What could be wrong?


If you planted your new roses straight into soil where other roses had recently been grown then it is likely that they are suffering from a problem known as replant disorderor rose sickness. This is characterised by poor establishment, dieback and a lack of healthy fine, feeder roots.


Stems and branches


The branches on many of my roses are dying back. What causes this?


Branch dieback on roses is very common, and it is unusual to see a rose bed without at least a small amount of die-back. There are a number of different causes.


Die-back can be a symptom of the root problems described above, as the plant struggles to take up water through its poorly-functioning root system.


Sometimes the die-back is the result of a fungal pathogen colonising the branches themselves. The fungi found most commonly are Paraconiothyrium fuckelii (a cause of rose canker) and Botrytis cinerea (grey mould). These fungi are quick to colonise the branches of roses that lack vigour (due to pests, foliar diseases, nutrient deficiencies, etc.), or branches that have suffered physical damage (e.g. from frost or poor pruningtechnique). Many of these factors can cause dieback in their own right, but colonisation of affected branches by the die-back pathogens can greatly increase the severity of the problem.


The stems and branches of my rose are covered in small, brown, limpet-like structures. What are they?


These are scale insects. The species found most commonly on roses is brown scale. A flat, circular whitish scale known as scurfy rose scale can also encrust the stems


Why has my plant developed a large, knobbly swelling near the base of the stem?


The most likely cause of this symptom is a bacterial disease called crown gall. The roots can also be affected.


How can I identify suckers on my grafted rose, and what can I do to prevent them from occurring?


Suckers (shoots produced from the rootstock) will develop from below ground level, and their leaves will often differ in appearance from those of the rest of the plant. For example, they may be a different colour (often paler) and/or have a different number of leaflets.


Suckers often develop if roots are injured, so avoid damaging the roots during digging or hoeing. To remove a sucker, dig down to expose its origin on the root, and then pull it away at this point; don’t just cut it off at soil level, or it will regrow.


If a rose is growing on its own root system it may still produce suckers from the roots, but these shoots will be identical to the rest of the plant and can even be used for propagation.


Leaves


Why have the leaves of my rose:


Become covered in a greyish-white, powdery growth?

Your plant has been attacked by the fungal disease powdery mildew.  Stems, flower buds and flowers can also be affected.


Developed dark spots? The leaves are turning yellow and falling.

This is rose black spot, a common and damaging fungal disease.


Developed small yellow spots on the top, with orange pustules underneath? The leaves are turning yellow and falling.

Your plant is affected by rose rust. The fungus produces orange spore pustules for much of the summer, but these are replaced by black ones in late summer/autumn.


Rolled downwards into a tube?

A pest called rose leaf-rolling sawfly is usually responsible.


Been eaten by gregarious caterpillar-like larvae?

The  larvae of large rose sawfly is most likely to blame.


Become shiny and sticky? Some also have a black growth on the top surface.

This is the result of aphid infestation. The shiny, sticky deposit is honeydew, and the black growth is sooty mould.


Had neat semi-circles or oval pieces removed from the edges?

The pieces of leaf tissue have been removed by female leaf-cutter bees, which use them to create the cells of their nests. No significant damage is done to the plant, and no control is necessary.


Become small, discoloured and strap-like?

This could be the result of virus infection, but a much more common cause is contamination of the plant by the weedkiller glyphosate. The leaves described above often develop in the season following contamination, in small clusters of pale green or pinkish-red leaves, resembling mini witches’ brooms.


Rose rosette virus, transmitted by microscopic eriophyid mites, is a problem in the USA and Canada, but is yet to be confirmed in the UK. Some of the symptoms produced are very similar to those caused by glyphosate contamination as described above. If you can rule out glyphosate contamination as the cause of the symptoms affecting your plant, and suspect that Rose rosette virus could be responsible, you should report this to the relevant plant health authority. Contact details can be found on the UK Plant Health Information Portal


Flowers


Most of the shoots of my rose have failed to produce flowers. What has gone wrong?

This is often the result of a poorly understood problem known as rose blindness.


My rose is a double-flowered variety. Many of the flowers turn brown and never open fully. What causes this?

This is a condition known as flower balling, usually caused by cool, wet weather.


My plant seems to be producing unopened flower buds within the petals of the original flower. Why has it done this?

This problem is known as proliferation. Again it is poorly understood, and could have more than one cause. Physical damage to the developing flower bud is thought to be a common cause – in this case flowers that develop later in the season should be unaffected. If a plant continually produces flowers showing this symptom then virus infection may be involved and it would be best to remove the plant.


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