Diseases & pests

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.

Potassium deficiency

Kalium-Mangel

You will notice potassium deficiency first on older, lower leaves: the edges turn yellow, brown and roll upward, while the veins stay green. In tomato the fruit at the stem base often remains hard and green (green collar), in potato and apple the leaves appear prematurely burnt and brittle. Because potassium is important for water balance and cell stability, affected plants wilt faster even on moist soil and react more sensitively to drought stress and frost.

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.

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 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.

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.

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.

Shot hole disease

Wilsonomyces carpophilus

Shot hole disease is caused by the fungus Wilsonomyces carpophilus and attacks above all stone fruit such as cherry, plum, peach and apricot. Typical are round spots with a red brown margin on the leaves, out of which the dead tissue falls, leaving the perforated, shot riddled look of the foliage. In addition, sunken spots with gummosis appear on the shoots, along with corky spots on the fruits. Where the attack is severe the tree loses its leaves early and is weakened.

Small Winter Moth

Operophtera brumata

You will notice the Small Winter Moth in spring by its green caterpillars that, when crawling, have a cat's hump appearance. They bore into buds, flowers, and young leaves from the shoot and leave holes. The females are wingless and walk up the trunks in mild late autumn to lay their eggs on the buds. When they multiply in large numbers, only the leaf veins remain on young shoots.

Spanish slug

Arion vulgaris

The Spanish slug is the most feared omnivore in the vegetable bed. It feeds at night and in damp weather, eating irregular holes into leaves, and often clears young lettuces or seedlings completely. The silvery shiny slime trails the next morning give it away. Soft, freshly planted batches are especially at risk.

Spotted Wing Drosophila

Drosophila suzukii

The Spotted Wing Drosophila (Drosophila suzukii) is a small fruit fly that, unlike native species, pierces healthy, still ripening fruits with its serrated ovipositor to lay eggs. The hatching larvae continue to feed inside, causing the fruit to quickly become soft, sunken, and begin to ferment. Thin-skinned berries and stone fruits are primarily affected; an infestation often only becomes apparent shortly before harvest through mushy spots and small larvae visible in the flesh.

Thrips (thunderflies)

Thysanoptera

Thrips are tiny, elongated insects that become particularly active on warm, muggy days, which is why they are also called thunderflies. They suck on leaves, shoots and flowers and leave behind silvery shiny patches as well as fine black specks of excrement on the underside of the leaf. Flowers often become deformed and get unsightly feeding damage along the edges, and young shoots can look stunted in growth. If you look closely, or with a magnifying glass, you can make out the slender, yellowish to dark insects between the petals.

Tomato leafminer

Tuta absoluta

The tomato leafminer (Tuta absoluta) is a small moth whose caterpillars feed inside the leaves and fruit of tomatoes and their relatives. Typical are pale, winding mines in the leaves, which turn brown and dry up; where the fruit is attacked, the caterpillars bore straight into the flesh. You can spot an infestation best by holding leaves up against the light: the tunnels and the small dark crumbs of frass inside them are then clearly visible. Left untreated, the pest can spread quickly across the whole plant and to neighbouring plants.

True powdery mildew

Erysiphales

You will see the true powdery mildew covering the upper leaf surfaces with a milky‑white coating that can be easily wiped off, unlike the false powdery mildew, which comes from below. It loves dry warm days with cool nights and especially weakens pumpkin family plants, causing the leaves to yellow and die.

Two-spotted spider mite

Tetranychus urticae

The two-spotted spider mite appears above all in dry heat in the greenhouse and sucks on the underside of the leaves, which makes the leaves first pale and speckled, then dull bronze coloured, before they dry up. With a heavy infestation, fine webbing covers the shoot tips. The animals, only 0.5 mm across, multiply at breakneck speed in the heat, so that a few mites can turn into a plague within two weeks.

Verticillium wilt

Verticillium dahliae

Verticillium wilt is a soil borne fungal disease that enters through the roots and blocks the plant's vascular tissue. Because water and nutrients can no longer get through, individual shoots or leaves wilt, often on one side only, and no longer recover overnight. Typical is a brown to greenish black discolouration in the wood, which you can see when you cut open an affected shoot. On maple and smoke bush a whole branch often dies back suddenly while the rest is still green. On tomato, aubergine, pepper and strawberry the plant struggles in summer heat and later collapses. The fungus forms resting bodies that survive ten years and more in the soil, which is why it keeps coming back on infected ground wherever susceptible crops are grown. The symptoms show above all in the warm summer, from June into October.

Vine Weevil

Otiorhynchus sulcatus

The vine weevil is the larva of the nocturnal beetle Otiorhynchus sulcatus and causes the actual damage. While the beetle leaves typical, notch-shaped feeding marks on the leaf edges above ground, the creamy white, C-shaped larva feeds on roots and the root collar underground. Affected plants such as Rhododendron, strawberry, or Hosta often wilt surprisingly, even though the soil is moist, because the water supply no longer works through the damaged roots. In cases of heavy infestation, you can almost lift the plant out of the pot without any roots.

Water vole

Arvicola terrestris

The water vole, commonly called a burrowing vole, lives underground and feeds on roots, tubers and the bark at the root collar. Typical are flat, arched mounds of soil in rows as well as tunnels close beneath the surface. Affected plants wilt abruptly or can be pulled up without effort, because the roots have already been gnawed away. On young fruit trees an attack at the root collar can lead to the tree dying within a short time.

Whitefly

Trialeurodes vaporariorum

The whitefly is a heat loving sap sucker that appears above all in the greenhouse and on container plants: larvae and pupae sit on the undersides of the leaves, and when the plant is knocked the white adults fly up in a cloud. Their sticky honeydew coats leaves and fruits and is colonised by black sooty mould; badly infested plants turn yellow and struggle. They can also transmit viruses.

White mould (sclerotinia)

Sclerotinia sclerotiorum

White mould is caused by the fungus Sclerotinia sclerotiorum and attacks many vegetable crops, especially lettuces and beans. Typical is a cottony, white fungal growth at the base of the stem that develops into black, irregular resting bodies (sclerotia). Infected plants wilt suddenly even though the soil is moist, because the inside of the stem rots soft and watery. The sclerotia survive in the soil for years and germinate again in damp, cool weather.

White mould (Sclerotinia rot)

Sclerotinia sclerotiorum

White mould, also called Sclerotinia rot, is a fungal disease with a broad host range that attacks lettuce, beans and many other crops. A watery, soft rot with a cotton wool like white fungal coating develops at the base of the stem; inside it, black, hard resting bodies (sclerotia) form, which survive in the soil for years. Affected plants wilt suddenly and fall over.

Wireworm

Agriotes spp.

Wireworms are the yellow-brown, hard larvae of click beetles and live several years in the soil. They bore narrow tunnels in potato tubers and carrots, making the harvest unsellable and often leading to rot through the wounds. The infestation is especially strong in areas that were previously meadow or heavily grassed.