Diseases & pests

Flower-end rot

Calcium-Mangel

Flower-end rot is not a disease caused by a pathogen, but a deficiency symptom. Growing fruits lack calcium at the fruit tip. A watery spot forms there, sinks in, and becomes leather‑like brown‑black. Often there is not too little lime in the soil; rather, the plant cannot transport calcium to the fruit under drought stress or overfertilisation.

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.

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.

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.

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 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.

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.

Iron deficiency chlorosis

Eisen-Mangel

In iron chlorosis, the newest leaves turn yellow while the veins stay green, a clear net pattern. Usually the soil does not lack iron, but it is unavailable to the plant at too high a pH. Blueberries and raspberries, as acid-loving plants, react especially sensitively, for example when the soil is too lime-rich or when you water with hard water.

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.

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 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.

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.

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.

Magnesium deficiency

Magnesium-Mangel

With magnesium deficiency, the leaf tissue between the veins lightens, while the veins remain green. Unlike iron deficiency, it begins on the older, lower leaves because the plant relocates mobile magnesium from old leaves to new growth. Tomatoes on light soils and apple trees with heavy fruit loads show this particularly in mid-summer.

Manganese deficiency

Mangan-Mangel

Manganese deficiency shows itself as a net like chlorosis: the leaf veins stay green while the areas between them fade to light green or yellow. The damage appears first on the younger and middle leaves in the upper part of the shoot and at first glance resembles iron deficiency, but differs through fine brown dots in the paled tissue. Affected above all are ericaceous plants such as blueberry, rhododendron and azalea, as well as grapevines, usually on soils with too high a pH. Where the shortage is stronger the shoot stays weak and leaves drop early.

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.

Nitrogen deficiency

Stickstoff-Mangel

Nitrogen deficiency arises when plants cannot take up enough plant available nitrogen from the soil, usually on exhausted or sandy ground. Because nitrogen is mobile within the plant, it moves the nutrient from old leaves into young ones, so the typical damage shows first on the lower, older leaves: an even, light green to yellow discolouration while the leaf veins mostly still stay green. Affected plants grow more weakly overall, stay smaller and yield less than healthy specimens. Where the shortage is severe the problem is especially quick to spot on cabbage, courgette or squash, in the form of pale, listless foliage.

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.

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 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.

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.