Graze, or Oak-leaf Syndrome, has been provisionally identified as a viroid, which, in practical terms, is a type of virus. Symptoms start as a change in texture and colour of the surface of a leaf, often only one leaflet of the pair being affected. Subsequent leaves may be much reduced in size and distorted, although many leaves show no symptoms. Ultimately the flowers also show slight distortion, by which stage the vase life is so reduced as to make them worthless. Both the development of the disease within individual plants, and the spread transmission between plants, seem to be more rapid as the ambient temperature increases. This disease appears to be more common in glasshouse grown cordon plants, and can have a significant effect on yield.
© 2006 P E M Rowland