Diseases & pests

Aphids

Aphidoidea

You will find that aphids are the most common sucking pests in your garden. They sit in dense colonies on soft shoot tips, suck plant sap and excrete sticky honeydew, on which black sooty mold settles. Severely infested shoots become stunted, and aphids also transmit viruses.

Apple Moth

Cydia pomonella

You are dealing with the apple moth, the cause of the classic worm-stung apples: The nocturnal moth lays eggs on young fruit from May, the hatched larva bores into the core and leaves a feces-filled tunnel. Infested fruit ripen early and fall. A second generation can occur in warm summer in August.

black vine beetle

Otiorhynchus sulcatus

You will find that the black vine beetle is a nocturnal, flightless beetle whose adults carve characteristic crescent‑shaped gouges into leaf edges. The larvae are more dangerous: they live in the soil and eat roots and root collars, so especially strawberries and blueberries wilt suddenly or die completely. Infestation is often only noticed when the plant is already stressed.

Brown china mark moth

Elophila nymphaeata

The brown china mark moth (Elophila nymphaeata) is a small moth whose caterpillars feed on floating leaved plants such as water lily and pond lily. The caterpillars cut oval pieces out of the leaves and spin them into small, floating cases in which they hide and go on feeding. You recognise the infestation by holed, window like translucent leaves and by the drifting little tubes of leaf pieces on the water surface. Where the attack is severe, whole floating leaves can fall apart.

Cabbage fly

Delia radicum

The cabbage fly lays its eggs at the root collar of crucifers, and the white maggots feed on the roots and root collars. Affected young plants wilt in the sun despite moist soil, turn bluish, and can be easily pulled from the ground. On kohlrabi and radishes, corky feeding sites with rot develop. The first generation in the cool spring is usually the most damaging.

Carrot fly

Psila rosae

The carrot fly lays its eggs at the root collar of umbellifers, and the maggots eat rust brown tunnels just under the skin of the root. Affected carrots and parsnips turn bitter and woody and rot quickly in store. A first sign is reddish discoloured foliage. The fly is on the wing in two to three generations from May into autumn.

Cherry fruit fly

Rhagoletis cerasi

You will see that the cherry fruit fly lays its eggs in mid May in sweet cherries that are just turning yellow; the hatched larva feeds inside the fruit and makes the cherry soft and rotting. You will find that mainly medium to late ripening varieties are affected. Very early varieties often escape the flight. The fly recognizes the ripening colour, which is why yellow sticky traps attract it.

Colorado potato beetle

Leptinotarsa decemlineata

You will notice the yellow-black striped Colorado potato beetle and its red larvae can strip a potato field bare in a few days. The females lay orange-colored eggs on the underside of the leaves; from them hatch the voracious larvae that cause the greatest damage.

Firebug

Pyrrhocoris apterus

The firebug (Pyrrhocoris apterus) is a noticeable, red-black patterned bug that likes to gather in large groups on sunny warm spots, often directly on the trunk of Stockrose, Malve, Eibisch, or Hibiskus. It mainly sucks on seeds and tender shoots, but usually causes little visible damage to the plant itself. You can recognize infestation by dense clusters of the insects, especially in spring and late summer at the base of the trunk and leaf axils.

Flea beetle

Phyllotreta

Flea beetles are tiny, black or metallic shiny beetles that jump away when touched. They punch countless small round holes in young leaves of Radieschen, Rucola and Rettich in dry-warm weather, making the leaves look like sieved. Seedlings can die completely under heavy infestation, while older plants usually tolerate the bite.

Fungus gnats

Sciaridae

Fungus gnats are small, black flies from the family Sciaridae whose larvae live in moist potting compost, where they feed on root hairs and young shoots. The adults are noticed above all when watering, when they rise from the surface of the soil in swarms. The actual damage is done by the whitish, black headed larvae: they weaken the roots, which makes seedlings and sensitive house plants such as begonia or fuchsia wilt or keel over suddenly. Seed trays and pots that are kept permanently moist are especially at risk.

Gooseberry sawfly

Nematus ribesii

The gooseberry sawfly (Nematus ribesii) lays its eggs on the undersides of the leaves of gooseberries and currants, where the green, black spotted larvae hatch. These caterpillar like larvae feed from the inside of the bush outwards, usually starting on the lower, shaded branches, and can strip a bush completely bare within a few days. You recognise an infestation by the rapid holing and skeletonising of the leaves and by the clearly visible groups of larvae when you turn the leaves over. Several generations can follow one another from April to August, so regular checks are worthwhile.

Grub beetle

Phyllopertha horticola

Grubs are the larvae of the garden chafer (Phyllopertha horticola) and usually live for one year, or up to two years in cooler locations, in the soil where they eat roots and tubers. Affected plants wilt suddenly, grow poorly, and can often be lifted out of the earth effortlessly. You can recognize the pest by the C-shaped, cream-white larvae with brown head capsules directly under the turf or in the root zone. In May and June, the adult, reddish-brown beetles swarm and prefer to lay their eggs in short-mown lawn.

Holly Leafroller

Cydalima perspectalis

The holly leafroller (Cydalima perspectalis) is the caterpillar of an invasive small moth and the most dangerous pest on holly. The caterpillars eat the leaves bare and leave dense webs and green droppings between the branches. If untreated, a heavy infestation can kill an entire plant within weeks. The caterpillars are recognizable by their green‑black striped pattern and black head.

Large White

Pieris brassicae

The Large White is the striking white moth whose yellow and black caterpillars can devour cabbage plants down to the leaf veins in a short time. The caterpillars live gregariously, so a single plant can become bare suddenly. The yellow egg clusters and the green and black droppings in the center are telltale signs. Two to three generations occur per year.

Leek moth

Acrolepiopsis assectella

The leek moth is a small nocturnal moth whose larvae bore into the leaves and stalks of leeks, garlic, and onions. They leave elongated, window-like translucent feeding marks and tunnels in the heart, through which rot often enters. Affected heart leaves bend or twist. In warm summers, two generations occur.

Lily beetle

Lilioceris lilii

The lily beetle (Lilioceris lilii) is a striking, bright red beetle that specializes in lilies, Fritillaria imperialis, and Fritillaria meleagris. Both the beetles and their larvae feed on leaves, shoots, and flowers; during heavy infestations, often only the leaf veins remain. You can recognize the larvae by the dark brown, slimy fecal matter they carry on their backs for protection. From April to August, the female lays orange eggs in rows on the underside of the leaves.

Mealybugs

Pseudococcus spp.

Mealybugs (Pseudococcus spp.) are small, sap sucking insects that camouflage themselves with a cottony layer of wax and prefer to sit in leaf axils, at shoot tips and along the leaf veins. They suck plant sap and excrete sticky honeydew, on which black sooty mould often settles. You recognise them by the white, woolly nests and by the shiny sticky film on the leaves and on the ground beneath. Container plants in their winter quarters are affected particularly often, because the dry, warm air suits the insects.

Onion fly

Delia antiqua

The onion fly (Delia antiqua) lays its eggs on the leaf sheaths of young onion plants, and the larvae then tunnel into the bulb, the neck and the roots. Affected plants show wilting, yellowish leaf tips, barely grow any further and can be pulled out of the soil easily. Inside the bulb itself you will find whitish maggots along with a rotten, often foul smelling consistency. Young plants and freshly planted onion sets are especially at risk from May to July, when the first generation of flies is on the wing.

Pear fly

Contarinia pyrivora

The pear fly is a small fly species whose larvae develop directly in the young flesh of pears. The small fly lays its eggs already in the bloom, so the damage only becomes visible when the fruitlets are pea‑sized: they remain small, become lumpy and develop dark bumps. Affected fruit usually fall already in June; if you cut them open, you find several yellowish‑white maggots in the brown, mushy flesh.

Pear leafhopper

Cacopsylla pyri

The pear leafhopper (Cacopsylla pyri) is a small jumping insect that feeds on pear trees and exudes sticky honeydew. The honeydew coats leaves, flowers, and fruits and often forms black sooty mold that hampers photosynthesis. You notice infestation by rolled, glossy sticky leaves, puckered spots on the fruits, and the tiny, hopping insects on the underside of the leaves.

Plum moth

Grapholita funebrana

The plum moth is the stone fruit counterpart to the codling moth: from June onwards the moth lays eggs on young fruit, the caterpillar bores its way through to the stone and triggers gummosis as well as premature, "false" ripening with fruit drop. Cut open fruit reveals the reddish caterpillar and a frass filled tunnel. In a warm late summer a more damaging second generation follows in August.

Rhododendron leafhopper

Graphocephala fennahi

The rhododendron leafhopper (Graphocephala fennahi) is a strikingly turquoise green leafhopper with orange red stripes that feeds on rhododendron and azalea from early summer into autumn. Its yellow green nymphs sit on the underside of the leaves as early as May, while the jumping adults appear from July. The direct feeding damage shows as pale, speckled patches on the leaves, but the real danger is the egg laying into the bud scales in late summer and autumn: this carries spores of the fungus Pycnostysanus azaleae into the wounds, and the affected flower buds turn brown to black and dry up over winter before they can open in spring. The best way to spot an infestation is by the clearly visible leafhoppers on the underside of the leaves and by the blackened, felty buds in late winter.

Rose sawflies

Endelomyia aethiops

From late June onwards the larvae of the rose slug sawfly (Endelomyia aethiops) scrape the leaf tissue from the upper side of the leaf and leave only the thin, translucent skin of the underside and the leaf veins standing. These window like patches soon dry to brown, so that infested leaves look scorched from a distance; later, holes and notches along the leaf margin are added. You can identify the yellowish green larvae with a yellow brown head, which look rather like small slugs, on the upper leaf surface of Rose, climbing rose and apple rose. In our latitudes the sawfly produces only one generation per year.