Diseases & pests

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.

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 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.

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.

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.

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.

Gray mold

Botrytis cinerea

Gray mold is a weak parasite that attacks wherever it is wet and cramped. On ripe strawberries, tomatoes or lettuce heads a typical gray‑fuzzy lawn forms, the fruits rot soft. Young plants can also collapse from it.

Hollyhock rust

Puccinia malvacearum

Hollyhock rust is caused by the fungus Puccinia malvacearum and attacks hollyhocks, mallows, marshmallow and mallow grown as a vegetable. You recognise it by yellowish spots on the upper leaf surface, matched on the underside by orange brown spore pustules. Where the attack is severe the leaves dry up from the bottom upwards and drop early, so that the plant looks increasingly bare over the summer.

Holly Twig Dieback

Cylindrocladium buxicola

Holly twig dieback is caused by the fungus Cylindrocladium buxicola and is one of the most serious diseases of holly. Early signs are brown spots on the leaves and black longitudinal streaks on young shoots, which spread quickly into entire brown nests in wet weather. On the underside of the leaf you often see a fine white fungal network, shortly after which the foliage drops in clumps and branches turn brown from inside out.

Late blight

Phytophthora infestans

You will find that the late blight is the most feared disease on tomato and potato. In warm wet weather the fungus spreads rapidly: first brown-grey spots on the leaves, then a white fuzz on the underside, finally rotting stems and fruits. Infected plants are often lost within a few days.

Leek rust

Puccinia allii

Leek rust is a fungal disease on leek, garlic, onion and chives. Bright orange yellow, elongated spore pustules form on the leaves and leaf sheaths, which burst open and dust off rust coloured powder. With a heavy infestation the foliage yellows and dies off prematurely. The leek stays usable, but grows more weakly and forms thinner stems.

Peach leaf curl

Taphrina deformans

Peach leaf curl affects peach and nectarine as soon as they begin to bud. The young leaves become blistered and thickened, curl up, and turn yellow-red to purple. In cases of heavy infection, the tree drops its leaves, produces new growth weakened, and suffers a significant loss in yield. The infection occurs exclusively during the cool and wet budding phase.

Pear net rust

Gymnosporangium sabinae

Pear net rust is a rust fungus with an alternate host: it overwinters on juniper and attacks your pear leaves in spring. Noticeable are the bright orange‑red spots on the upper side and the net‑like outgrowths on the underside of the leaf. Without a juniper within a few hundred meters of you, the fungus cannot complete its cycle.

Phytophthora root and shoot rot

Phytophthora spp.

Phytophthora root and shoot rot is caused by soil borne fungi of the genus Phytophthora, which become active above all where there is waterlogging. Affected plants wilt despite moist soil, leaves turn pale or reddish and individual shoots die back. At the root collar, once exposed, a dark, pulpy bark shows with a sharp boundary to the healthy wood. Without countermeasures the whole plant can die within a few weeks.

Rhododendron bud blast

Pycnostysanus azaleae

Rhododendron bud blast is caused by the fungus Pycnostysanus azaleae and attacks above all rhododendron and azalea. Affected flower buds turn brown to greyish black, dry up and no longer open in spring; they often stay hanging on the shrub for months or into the next year. In autumn and winter you recognise the fungus by fine, bristle like black fruiting bodies growing out of the bud scales. The fungus frequently uses the feeding punctures of the rhododendron leafhopper as its point of entry, which is why bud blast often occurs together with leafhopper infestation.

Rose rust

Phragmidium mucronatum

Rose rust is a fungal disease caused by Phragmidium mucronatum that occurs above all on roses, climbing roses and apple roses. It is characterised by orange yellow, powdery spore pustules on the upper leaf surface and cushion shaped rust brown pustules underneath. In late summer the spore pustules often turn dark brown to black. Where the attack is severe the leaves turn yellow and drop early, which weakens the plant.

Septoria leaf spot

Septoria spp.

Septoria leaf spot is a widespread fungal attack that affects above all tomatoes, celery, parsley and phlox. Typical are small, round to angular grey brown spots with a dark margin, in the middle of which you can make out fine black dots on close inspection. The attack usually begins on the lower leaves near the ground and moves upwards in damp weather. Left untreated, the leaves turn yellow and dry up, which weakens the plant and reduces the yield.