Adverse factors leading to plant stress and dieback include:
- Bad planting technique – avoid planting the rose with the graft union buried below soil level
- Soil conditions that are too wet or dry
- Poor pruning technique, particularly where the buds are damaged or long pruning stubs are left above them
- Physical damage, for example that created when crossing branches rub together
- Frost damage
- Severe defoliation by insect pests
- Severe outbreaks of foliar diseases such as black spot, rust or powdery mildew
- Root disease problems, e.g. honey fungus or Phytophthora root rot
- Replant disease, resulting from planting new roses directly into soil that has previously grown roses
Shoots, branches and stems suffering from physical damage, or those already showing dieback due to one or more of the factors listed above, are often invaded by a range of fungi that can cause further damage. Once within the plant these fungi can spread into adjacent healthy tissues, and in severe cases may lead to extensive dieback or even death of the plant.
Two diseases commonly associated with rose dieback are grey mould (Botrytis cinerea) and rose canker (Paraconiothyrium fuckelii, syn. Leptosphaeria coniothyrium). The former, as its name suggests, is sometimes seen as a fuzzy grey mould (particularly on dead flowers and frost-damaged shoots), although this growth may not be present where the fungus has colonised woody tissues.
Paraconiothyrium fuckelii is the most common cause of canker on roses, and can be very destructive. Infection often occurs through bad pruning cuts or injuries to the crown. It produces tiny black fruiting bodies that are sometimes just visible on the bark of affected branches or stems. This fungus also causes cane blight disease of raspberries.