Foam on a stem, small holes in leaves and white flecks on petals each point to a different sap-feeding insect in the advice of the Royal Horticultural Society (RHS). This guide summarises the RHS pages for cuckoo spit, capsid bugs and thrips, read on 25 October 2026; none of the pages shows a date. The pages refer to Britain and the UK. General information, not a treatment recommendation.
White froth on stems in late spring: cuckoo spit
The RHS says cuckoo spit is a white frothy liquid secreted by the nymphs of sap-sucking true bugs called froghoppers, also known as spittlebugs. It has no connection with the bird. The page lists ten species of froghopper in the UK, across two families, and plants affected that include chrysanthemum, dahlia, fuchsia, lavender, rosemary, rose and willow.
- Blobs of froth develop on young stems and leaves in late spring and summer, and the RHS gives May to July as the most active period.
- Each blob contains a creamy white nymph up to 4-6 mm long.
- Usually plant growth is unaffected, but a nymph feeding at a shoot tip may cause some distorted growth.
The RHS calls cuckoo spit harmless and says the insects are part of the biodiversity a healthy garden supports. Adult froghoppers appear in mid to late summer, live openly on plants and do not produce the froth or cause noticeable damage. Eggs are laid in plant stems in late summer and the nymphs hatch in spring. The page adds that Xylella, a bacterial plant disease causing serious problems in Southern Europe, is spread by insects that feed on the xylem of plants, which includes froghoppers, and has not yet been detected in Britain. It says spittlebugs are not a pest and asks gardeners not to remove them.
Small brown-edged holes from May: capsid bugs
Capsid bugs belong to the family Miridae, which the RHS says has over 200 species in Britain. Most feed on plant sap, though most do not affect garden plants and some are predatory. A few feed at shoot tips and flower buds of garden plants, especially fuchsia, dahlia, rose and hydrangea; the RHS names the common green capsid and the tarnished or bishop bug. The apple capsid feeds on apple and pear and can affect the fruit.
Signs of damage appear from May to early September. Leaves near the shoot tips develop many small, brown-edged holes and may be misshapen. Affected flower buds, particularly those of fuchsia, may fail to develop, while daisy-like flowers such as chrysanthemum and dahlia may open unevenly. Apple capsid can cause bumps or raised corky growths on mature fruit; the RHS says these blemishes are superficial and do not affect the eating and keeping qualities of the fruit.
The RHS says the presence of capsid bugs is not unusual and that they are part of a functioning garden ecosystem. Its management advice is to tolerate some damage, because by the time distorted leaves are noticed it can be too late for control measures, and plants often recover. Vegetables do not need treating. It also suggests encouraging predators such as birds and ground beetles, removing unwanted plants that can act as alternative hosts where capsids have been a problem, and clearing dead vegetation in late winter, which may destroy overwintering sites for the tarnished plant bug.
Silvery mottling and black specks: thrips
Thrips are an order of insects with around 150 species in Britain, according to the RHS, and many do not cause noticeable damage. Adults are narrow-bodied and up to 2 mm long. The RHS says they can be hard to detect, and that shaking foliage over a white sheet of paper reveals them for examination with a magnifying lens.
Leaves fed on by thrips often become dull green and later develop a silvery-white discolouration on the upper surface, marked by many tiny black excrement spots. Petals can show white flecking, and heavy feeding on flower buds may stop them opening. Some thrips, such as onion thrips and western flower thrips, can transmit plant viruses. The RHS gives April to September as the most active period.
For control, the RHS says established outdoor shrubs usually survive extensive silvery mottling from glasshouse thrips and that some damage can be tolerated. It also mentions natural enemies such as the predatory bug Orius laevigatus, which can occur naturally. Biological controls are available for glasshouses, and the page notes that the nematodes can potentially affect other insects and the predators can feed on invertebrates other than thrips. When buying houseplants, the RHS advises checking the flowers and avoiding any showing signs of thrips or pale flecking. The guide to buying predators and nematodes covers timing and handling in more detail.
Sticky traps and proportion
The RHS describes cuckoo spit as harmless, capsid damage as something to tolerate and outdoor thrips damage as often survivable. On traps, its thrips page says hanging blue sticky traps above or among plants in glasshouses can trap thrips and help monitor and reduce numbers, but that this is not recommended out of doors because the traps capture a large number of non-target invertebrates. Other sap-feeders are covered in the guides to ants and aphids and to mealybugs and scale insects.
FAQs
Does cuckoo spit damage the plant?
The RHS says it is harmless and that plant growth is usually unaffected, although a nymph feeding at the shoot tip may distort growth.
Are sticky traps suitable for thrips in the open garden?
The RHS describes blue sticky traps for glasshouses and says they are not recommended out of doors, because they capture a large number of non-target invertebrates.
The bottom line
For froth on stems, the RHS describes cuckoo spit as harmless and its froghopper nymphs as part of a healthy garden. For holes and distorted shoot tips from May, it identifies capsid bugs and advises tolerating some damage and encouraging predators. For silvery mottling with black specks, it points to thrips and says established outdoor shrubs usually survive, while it does not recommend sticky traps out of doors. This is general information, not a treatment recommendation.
Sources
- Cuckoo spit (spittlebugs) (rhs.org.uk)
- Capsid bugs (rhs.org.uk)
- Thrips (rhs.org.uk)