How to recognise it
There are several different causes of cankers (and the associated die-back) in roses, each having slightly different symptoms:
Stem canker
This is this most widespread and damaging of the rose cankers. Stems develop brown, cracked and sunken areas, which are sometimes reddened around the border. The lesions gradually grows larger and may eventually girdle the entire stem, causing die-back of higher growth. Tiny black growths form on the surface of the canker (this is the fungus reproducing). Stem canker often occurs when roses are budded, the infection spreading upwards and downwards from the budding site.
Brown canker
This canker starts off as red spots on the stem, which then become whitish patches and develop into light brown cankers, which may have purple margins and tiny black growths on the surface. The stem is often girdled by the infection and the growth above it will either die-back or form knobbly growths.
Brand canker
Like brown canker, this starts life as red spots on the stem, which then form small pale brown areas at their centres. In spring these areas may appear black. Tiny, black growths may appear on the spots. Eventually the spots will merge together, girdling the stem and causing die-back.
Clathridium canker
Small brown dips appear in the stem with purple margins. They usually stay on just one side of the stem (often associated with a small wound on the stem) but occasionally will grow to girdle the stem. The cankered areas remain smooth and tiny black growths may appear on them.
Grey mould die-back
A grey mould infection often enters at the apex of stems, on old flowers, fruit stalks or stems which have died back. It is often associated with damage to the stem tip by cold conditions or frost. The grey, fluffy growth which is typical of grey mould may or may not be present.
Briar scab
No apparent canker is visible, but black, crusty growths appear on the stem, often around the rose’s thorns. This canker is more common on wild roses, although it can occur on cultivated roses.
Why it’s a problem
Cankering will eventually kill the stem growth above the point of the canker. If allowed to spread unchecked this can affect much, if not all, of the plant.
Where you are likely to find it
Generally only found on roses (cultivated and wild) although it may also occur on other members of the Rosaceae family.
How to prevent it
The infection enters through points of weakness, such as pruning cuts, small wounds or dormant buds. Always ensure any dead/damaged flowers, buds and shoots are removed promptly to reduce the possible points of entry for the disease. Ensure that all pruning cuts are made cleanly.
How to get rid of it
Cut out any stems showing signs of canker, to an appropriate point below the area of infection. If the plant is badly infected then it should be removed. Ensure that any removed wood is burnt or disposed of through municipal waste collection – do not leave it lying around the garden where it might infect other plants.
Fungicides are not generally effective against cankers, although they may help to limit the spread of an infection.
Is it good for anything?!
No.
Other useful information
Cankers and die-back can also be caused by other factors such as root damage or cold temperatures – by viewing our ‘woody stem symptoms‘ information.
