How to recognise it
The adult is bright green and measures about 5mm in length, resembling a large aphid. The nymphs (similar to the adults but without wings) are yellow-green in colour. Careful inspection may reveal capsids, but they quickly drop to the ground or fly away when disturbed so you may never see them.
Foliage has distorted growth with small brown spots which become holes, turning raggedy edged as the leaf expands. Buds and shoots can be damaged, turning brown and withering or causing flowers to open lop-sided. Fruit can be scarred with bumps and other irregularities.
Most of the damage is done in late spring and summer.
The adults lay eggs on young twigs of woody host plants (eg apples, currants, hawthorns) in autumn, which overwinter and hatch as nymphs in the spring. The nymphs feed on the new growth and then migrate to herbaceous plants for the summer. The females mature on the herbaceous plants and lay eggs in the stems and petioles during June and July. This second generation hatches and matures to adulthood in autumn, the females laying eggs to overwinter before dying.
Why it’s a problem
Its salivary juices (which it injects into the plant when feeding on the sap) are poisonous, causing the telltale leaf, bud and fruit distortions.
Where you are likely to find it
On fruit trees, shrubs and flower crops (such as dahlias and chrysanthemum), usually outside. The adult capsid can fly from plant to plant.
How to deter it
Clear up debris and fallen leaves in winter, particularly under hedges, which may be providing overwintering accommodation for the eggs.
How to get rid of it
This isn’t usually serious enough to merit chemical treatment, but if the damage is particularly unsightly or affecting soft fruit crops, an insecticide such as pyrethrin, a synthetic pyrethroid compound such as bifenthrin, or thiacloprid can be used on the plant and surrounding ground. This can be done in December or January when the plants are dormant, but this will not protect the plants from re-invasion in the spring, so spraying in May, June and July when the pests are active will be more effective. Spray strawberries, raspberries and loganberries immediately before flowering and apples, pears, plums, currants and gooseberries immediately after flowering. Ornamental plums should be sprayed in spring and summer and may need a further application later in the year.