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.

Apple powdery mildew

Podosphaera leucotricha

Apple powdery mildew is caused by the fungus Podosphaera leucotricha and appears as a white, powdery coating on young leaves, shoot tips, and flowers. Infected leaves curl in and grow stunted, shoot tips often dry out completely. Flowers remain small and grayish, many fall off before fruit set. The easiest way to detect infection is on newly emerging shoots in spring, where the white coating is most visible.

Apple scab

Venturia inaequalis

Apple scab is the most common apple disease in humid areas. On leaves and fruit you see olive‑green to black, rough spots; the fruit corks and splits open. They remain mostly edible in taste, but look unsightly and store poorly.

Bean rust

Uromyces appendiculatus

Bean rust is a fungal disease that occurs above all in high summer on bush beans, pole beans and runner beans. Characteristic are rust brown, powdery spore pustules on the underside of the leaf, surrounded by a yellow halo. Badly infested leaves turn yellow and drop early, which weakens the plant and reduces pod set.

Black spot

Diplocarpon rosae

Black spot is the most important leaf disease on roses. Characteristic are the black spots with star shaped frayed edges, around which the leaf turns yellow. Badly infested roses lose their foliage early, weaken and flower less. The fungus overwinters in the fallen leaves and on the shoots.

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.

Blossom wilt (Monilia twig blight)

Monilia laxa

Blossom wilt infects stone fruit through the open flower and travels from there into the shoot. Affected blossoms and shoot tips wilt abruptly and dry up brown, as if frost had caught them. That is why it is often mistaken for frost damage. Sour cherries such as ‘Schattenmorelle’ are particularly susceptible when the weather is cold and wet at flowering time.

Boll rot disease of beans

Colletotrichum lindemuthianum

The boll rot disease is a fungal disease on bush, pole, and fire beans, which mainly distorts the pods. Typical are dark brown to black, sharply bordered and sunken spots with a pale center, from which pinkish spore masses ooze when wet. Infected pods are unsellable, and the fungus moves into the seed, carrying it into the next year.

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.

Brown rot (fruit rot)

Monilia fructigena

Brown rot makes ripening fruit rot brown on the tree and in store. Cushion like spore pustules arranged in rings form on the rotten patches. The fungus almost only enters through injuries: wasp damage, hail or scab cracks are the typical points of entry. The dried up mummified fruits on the tree are the source of infection for the following year.

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.

Carrot leaf blight (Alternaria)

Alternaria dauci

Carrot leaf blight is caused by the fungus Alternaria dauci and is one of the most common leaf diseases on carrots and related umbellifers. You can recognise it by the blackish brown, irregular spots on the leaflets, which spread quickly in wet weather and cause the foliage to dry up. With a heavy infestation the tops die back so far that harvesting becomes difficult, while the root itself usually stays undamaged.

Celery leaf spot

Septoria apiicola

Celery leaf spot is the most important fungal disease on celeriac and celery. Roundish, light brown spots with a dark margin form on the leaves, with tiny black dots in their centre: the spore containers of the fungus. With a heavy infestation the foliage yellows over large areas and dries up, which noticeably reduces the yield and the size of the bulbs.

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.

Clubroot

Plasmodiophora brassicae

Clubroot is a soil-borne fungal disease caused by Plasmodiophora brassicae that affects all cruciferous plants. The pathogen enters through root hairs and causes the roots to swell into knobby, thickened outgrowths that block water and nutrient transport. You recognize infection by wilting plants in sunshine, disturbed growth, and lack of head formation; when you dig up, the typical root swellings appear, which later rot. Spores remain viable in the soil for many years, so prevention is more important than late intervention.

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.

Drought stress (water shortage)

Wassermangel

Drought stress arises when plants cannot take up enough water over a longer period, usually during persistent heat with no rain. Typical signs are wilted, drooping leaves that no longer recover during the day, along with brown, crispy leaf margins. Shallow rooters such as hydrangea and rhododendron react particularly quickly, because their roots barely reach any reserves in the deeper soil. Left untreated, leaf drop and flower drop follow, and on vegetables such as tomato and cucumber blossom end rot and small, hard fruits.

European canker

Neonectria ditissima

European canker is caused by the fungus Neonectria ditissima and attacks above all pome fruit such as apple, pear and quince. Typical are sunken, ring shaped wounds on branches and shoots, around which the bark bulges like a wall and thickens in concentric layers. Where the attack is severe the shoot dies above the wound, and in winter small reddish spore pustules often appear on the diseased bark. Blossoms and fruits can rot too and dry out into mummified fruits.

False Mildew

Peronosporaceae

You will find that the False Mildew is not a true fungus, but an oomycete that comes from the underside of the leaf, unlike the True Mildew. On the upper side you see yellow‑square spots, below a gray‑violet coating. On cucumber, onion and lettuce it can collapse entire stands within a few days once it is wet and warm.

Fireblight

Erwinia amylovora

Fireblight is a highly contagious bacterial disease of stone fruit and related rose plants, and in many states it is reportable. Infected shoot tips wilt, turn brown‑black, and bend hook‑shaped into a herder's staff; under damp heat milky slime droplets exude, spreading the bacterium further. If untreated, a tree can die within a season.

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.