What are mounds of petunias

Plant pests: the 10 most important types and how to spot them

Whether on the houseplants in the house or the vegetables outside in the garden: plant pests are everywhere. But if you want to fight it successfully, you have to know exactly what type of pest it is.

Some plant pests can be identified at first glance, while others are so similar that you have to take a closer look. Some can be recognized by the typical damage that they leave on a plant. With our overview of the most important plant pests, you can reliably identify the pests in your garden and take appropriate countermeasures.

Aphids are among the largest group of pests in the garden. Depending on the species, they are green, yellow, red, black or gray-white and are two to ten millimeters long. The insects have six legs, two long antennae, a powerful proboscis and two backward-facing "tubes", the so-called siphons. In small colonies, the aphids are often well camouflaged on the underside of the leaves. This can also include winged specimens. With their proboscis, aphids dig deep into the leaves and suck out the cells. The infected plants suffer from stunted growth and different degrees of leaf deformation. The leaves are covered with the sticky excrement of the lice, the sweet honeydew. All sorts of sooty fungi like to settle on it.

The gardeners are particularly troubled by the nudibranchs. One of the most common species is the large slug, which is 10 to 15 centimeters long and is reddish, brown or black in color. The mollusks are usually active at night and hide under stones or in other moist shelters during the day. The typical damage caused by snails includes irregular feeding holes on leaves, flowers and stems. Since slugs protect themselves from drying out by secreting mucus, shiny silver traces often reveal the presence of the plant pests.

Voles differ from their relatives from the group of real mice in their short tail, plump body, small ears and round head. The rodents feed mainly on root and tuber vegetables such as celery and carrots, tulip bulbs and other subterranean plant parts. They also like to nibble on the bark of trunks and branches of young trees.

Similar to moles, voles create a branching system of ducts underground. In the case of the vole heaps, the hole is not in the middle under the hill, but is slightly offset to the side. It often contains roots and parts of plants and is usually not as high as a molehill.

Scale insects, like aphids, are sap-sucking insects. Close together, they like to attack the leaves and shoots of outdoor, greenhouse and indoor plants, which they weaken with their sucking activities. Depending on the species, the scale insects are between one and six millimeters in size and like to hide under a waxy secretion that covers them like a shield. Newly hatched scale insects are still mobile and are looking for a suitable feeding place. Once you have found one, you won't leave it for the rest of your life. Their protective shield is usually brown or gray-white and flat to dome-shaped. Some species secrete honeydew, which adheres to the foliage as a sticky coating.

Mealybugs, which count among the scale insects, like to infest succulents and cacti, but also other indoor and greenhouse plants are not spared from them. The soft mealybugs are gray-white or reddish and grow up to four millimeters in size. They like to colonize leaf axils or other parts of plants that are difficult to access. Characteristic of mealybugs is the secretion of white, woolly, crinkled wax threads. The plant pests can therefore be easily recognized by the cotton balls under which they live and with which they also cover their eggs. In plants infected by mealybugs, the leaves turn yellow, curl up and eventually fall off. Sticky honeydew is also an indication of mealybugs.

Depending on the species, spider mites are only a maximum of one millimeter in size and are therefore particularly noticeable on the infested plants because of their webs and sucking damage. An important feature: when spider mites suck out the cells of the leaves, fine, light speckles appear on the upper side of the leaf.

Only on closer inspection, for example with a magnifying glass, can one discover the tiny spider mites and their round eggs on the underside of the leaf. When the spider mites appear in large numbers, they often cover the leaf margins and leaf axils of the infected plants with fine webs. The leaves dry up and fall off prematurely.

The whitefly is also an insect that likes to suck out the cell sap from plants. It is around two millimeters in size and develops pure white wings when fully grown. White flies prefer to sit on the underside of the leaf, where they also lay their eggs. If you move the leaves, they will fly open. Flat, oval larvae that are reminiscent of scale insects hatch from the eggs. Even the larvae secrete sugary honeydew, which often drips onto the upper side of the leaves below. Affected leaves become blotchy and yellow.

Thrips are narrow, up to two millimeters large insects that particularly like to feed on the cell sap of indoor plants. In contrast to most other plant teats, they also sit on the upper side of the leaf. They cause fine, silvery, shiny speckles on the leaf surface. In the event of a strong thrips infestation, the plants react with severe growth disorders. Even small brown pebbles of excrement can expose the plant pests. The adult animals are usually black and have two pairs of hairy wings that, when at rest, fold flat on their abdomen.

The box tree moth is a white butterfly about four centimeters tall with a black-brown border. Its caterpillars, which can grow up to 50 millimeters long and are well camouflaged by their green-black pattern, eat the box leaves down to the skeleton. The bushes become bare and brown over time.

The caterpillars eat so hidden inside the box trees that they can hardly be seen from the outside. A clue are the green crumbs of excrement under the box trees. The young caterpillars of the boxwood moth overwinter in a dense web between leaves and on branch forks. In spring they hatch and start eating the leaves.

From the end of May you can spot the black, 10 to 12 millimeter long weevils when they climb up the house wall. During the day, the nocturnal beetles usually hide under stones, in cracks in walls or in layers of soil near cultivated plants. At night the black weevil feed on bays in leaf margins, preferably rhododendron, cherry laurel or strawberries. In summer the black weevils lay up to 1,000 eggs. The larvae cause the greatest damage by eating the fine roots or tubers under the plants.