How to recognise it
Shoots become abnormally wide and flattened, looking as if several shoots are fused together.
What causes it
It is not currently known for sure what causes fasciation, but in some cases it seems to be connected to damage to the point at which the shoot grows from the stem, caused by insects, slugs, frost or poor handling. It may be caused by bacterial infection or genetic mutation.
Why it’s a problem
It isn’t really – leaf and flower formation are not affected (although fasciation of flowers does occasionally occur, but it does not spread from flower to flower).
Where you are likely to find it
On many shrubs, including forsythia, daphne, Prunus subhirtella ‘Autumnalis’ and roses. Also occurs on some herbaceous perennials including delphiniums.
How to prevent it
Avoid damage to stems.
How to get rid of it
If you find it unsightly, simple prune out the offending stems. However, it does no harm and can be left on the plant.
Is it good for anything?!
Flower arrangers use some varieties of fasciated stems in arrangements.