Pests and Diseases - Which pest or disease do my plants have?
Plant Pests - this page  Diseases - fungus

Slugs and Snails

Signs - Irregular holes are eaten from leaves, slime trails often left around the plants on the soil and the leaves

Damage - Young plants and seedlings are particularly vulnerable and can be stripped bare or eaten down to the ground. Particularly fond of Hostas and Delphiniums.

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Aphids

Signs - Usually thought of as greenfly, but can be black, yellow, pink, greyish-white and brown. About 2mm long when fully grown, roundish.

Damage - Heavy infestations can reduce the vigour of a plant and leave it vulnerable to attack by other pests and diseases. Frequently spread virus diseases as they move from one infected plant to another. Virus disease usually characterised by irregular yellow patches on the leaves which may be wrinkled but otherwise alive.

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Caterpillar

Caterpillars

Signs - Leaves stripped, or eaten from the outside edge inwards. May not always be easily visible as they can be well camouflaged. "Frass" may be seen, tiny black balls of excrement. More cunning and smaller types "mine" leaves between the upper and lower surfaces.

Damage - Young leaves can be eaten away and more mature plants are left with unsightly holes.

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Chafer beetle larvae

Signs - Not specific to chafer beetle larvae and can seem in the early stages like drought or stress. Patches of affected lawn wilt and turn yellow or brown. On investigation, the grass can be lifted easily from the soil not held down by roots to any degree. 

Damage - dead patches of lawn, may be made worse by animals such as birds foxes or badgers ripping up the grass to get at the larvae. Damage usually occurs during the autumn and is more common on light sandy soils where grass growth is already poor.

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Leatherjackets

Signs - affected plants may turn yellow, wither and die. Small plants and seedlings may be severed at ground level. The grey - brown leatherjackets are up to 3.5cm (1 1/2inches) long, smooth, tubular and legless, rarely seen above ground, usually found just below the surface particularly in grass where a small population that causes no visible damage is more common than not.

Damage - feed on roots particularly affecting young annuals, bulbs and vegetables, predominantly affects land that has been recently brought into cultivation recently and usually subsides after a couple of years. On lawns, more damage is usually done by birds and small mammals digging the leatherjackets up than by the leatherjackets themselves.

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Lily beetle

Signs - Cleanly cut holes in lilies and Fritillaria. The easiest way to see the adults is to bend at the waist and turn your head upside down so you are looking up the stems and at the bottom of the leaves rather than down on the stems. If you find one lily beetle, you can bet you'll get lots more.

The larvae are very inconspicuous as they cover themselves with sticky black excreta which if you've never seen them before doesn't look anything like an insect that can devour your lovingly cared for lilies in next to no time.

The eggs are tiny, but are bright orange/red and laid in groups of up to 15, so they are surprisingly easy to see for their size - they are only laid on the underside of leaves.

Damage - leaf eaters - the years flowers can rapidly be completely destroyed before you have even seen them unfurl as small buds. They will also start on the leaves and strip them.

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Mealybugs

Signs - small fluffy white lumps about 5mm (1/4") appear on plants, often in the axil - where the leaf meets the stem. Leaves turn yellow and may wilt and die.  Usually affect house and greenhouse plants, but also Pyracantha and fruit trees. Stick honeydew and black sooty moulds may accompany. Despite being insects, they don't look like insects, just a shapeless piece of cotton wool.

Damage - plants are rarely killed unless very heavily infested over a long period. Commonly weakened, a heavy infestation is very unsightly from the pests themselves and from the sticky honeydew that they secrete and possibly even black moulds that grow on the sticky honeydew. Root mealy bugs damage the roots.

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Red spider mite

Signs - Leaves become speckled, as though covered with hundreds or thousands of pale dots giving a rather ill-looking and "dusty" appearance. Heavily  infested plants may become covered with fine webs. the mites themselves are less than 1mm long and not easy to see clearly.

Damage - Sap feeders which weakens the plant. Usually a problem in house and greenhouse plants as they like a dry atmosphere, can be a problem outside in hot, dry summers.

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Vine weevils

Signs - Irregular notches taken from the margins of the leaves are made by the adult weevil. If a plant suddenly dies and appears to have no roots, this is the work of the larvae. The way you find out is by looking at a poorly looking plant, when you go to pick off a dead leaf, the whole lot lifts from the roots in your hand - it's a bit late by then though. Adults may be seen around plants, look for cream / white larvae in compost when re-potting plants.

Damage - Depends on the size of the root system and the number of grubs eating it. Growth will slow, the plant may then begin to wilt and finally die as it no longer has sufficient roots to sustain it. Unfortunately by the time it has been discovered it is usually to late to take steps for that plant, though others not so far gone can be protected.

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Whitefly

Signs - Most commonly found on houseplants and in greenhouses, when disturbing the leaves, the tiny white flies that hide under the leaves will fly up.

Damage - Sap suckers, will weaken the plant and make it susceptible to further attacks of pests and disease.
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