Plants affected
Many plants, including chrysanthemum, dahlia, fuchsia, lavender
(illustrated), rosemary, rose and willow.
Symptoms
Blobs of frothy liquid on young stems and leaves in late spring and summer.
Cause
Apart from appearing about the same time as cuckoos are heard, the froth has no connection with any bird. Instead it is secreted by the immature stages of sap-sucking insects known as froghoppers, presumably as a means of protecting themselves against predators. The adult insects live openly on the plant and do not produce any cuckoo spit.
Control
Apart from the 'spit' these insects have little detrimental effect on the plants and can be tolerated. If you wish, they can be wiped off by hand or dislodged with a jet of water from a garden hose. It is not worth using an insecticide against froghoppers.
Andrew Halstead