Capsid bugs are members of the true bug family Miridae, true bugs have sucking mouthparts. There are over 200 species of mirid bug in Britain. A majority feed on plant sap, most do not affect garden plants, some species are predatory.  Some capsid bugs are a natural part of any garden. 

A few species do feed on plant

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

Some capsid bugs have a more restricted host range such as the apple capsid (Plesiocoris rugicollis), which feeds on apple and pear and can affect fruits.

Signs of damage appear from May to early September.

• As capsid bugs feed, they damage and kill some of the cells where the mouthparts have probed 
• The 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, or, in the case of chrysanthemum, dahlia and other daisy-like flowers, open unevenly
• Apple capsid (Plesiocoris rugicollis) damages the foliage and also feeds on young fruitlets, which results in bumps or raised corky growths developing on the mature fruit. These blemishes are superficial and do not affect the eating and keeping qualities of the fruits. Apple capsid can also affect pear

Check susceptible plants frequently from early spring onwards so action can be taken before a damaging population has developed. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.

Non-pesticide control

• Apple cultivars vary in susceptibility to apple capsid – the fruits of Charles Ross’, ‘Allington Pippin’ and ‘Edward VII’ are some which may be extensively marked by capsid bumps
• If capsid bugs have been a problem in the past removing unwanted plants which can act as alternative host plants can reduce the problem
• Removing dead vegetation in late winter may destroy overwintering sites for the tarnished plant bug
• Tolerate some damage, by the time distorted leaves are noticed it can be too late to take control measures. Often the vigour of plants is unaffected and they soon recover. Vegetables do not need treating 
• Encourage predators and other natural enemies in the garden such as birds, hedgehogs and ground beetles

Pesticide control

• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) can give good control of capsid bugs. These pesticides have a very short persistence and so may require reapplication to keep capsid bug numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
• Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against aphids (e.g. Ecofective Bug Control, Growing Success Bug Stop, Rose Clear 3 in 1 Action SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These products contain some synthetic ingredients and so are not considered organic
• More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
• A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval. Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

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• Adult capsid bugs are green or brown and up to 6mm long (¼in). Capsid bug wings are folded over the abdomen and have the basal two-thirds coloured and thickened, the outer third is translucent, which shows as a clear diamond-shaped area at the rear end of the insect. Species that do not affect garden plants can be very similar in appearance
• Nymphs are wingless and generally pale green in colour 
• Apple capsid overwinters as eggs that are laid in the bark of apple branches and shoots, these eggs hatch in April to May. They become adult in June and July and there is one generation a year
• Common green capsid overwinters as eggs inserted into a range of trees and shrubs. They eggs hatch in spring and become adults by July. These lay eggs and produce a second generation before the winter
• The tarnished plant bug overwinters as an adult in sheltered places. They emerge in spring and lay eggs on a wide range of plants. There are two generations a year