Scale insects are among the most common pests on house and garden plants. The little animals sometimes cause great damage, especially to hard-leaved plants as well as fruit and ornamental trees. How to effectively combat the plant suckers and ensure that your plants are not infested in the first place.

Ladybugs fight scale insects

Table of Contents

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  1. the essentials in brief
  2. identify scale insects
  3. Causes and Prevention
  4. fight scale insects
  5. frequently asked Questions

    6. the essentials in brief

    • Scale insects are among the most common pests on both indoor and garden plants.
    • There are various species that primarily attack hard-leaved and evergreen plants as well as fruit and ornamental trees.
    • They are often difficult to detect in the early stages and can cause great damage.
    • The best way to combat scale insects is with a mixture of soap and alcohol or with nettle manure.

    identify scale insects

    Scale insects (lat. Coccoidea) form a very species-rich family within the plant lice (lat. Sternorrhyncha). There are around 4000 different species worldwide, but only around 90 are native to Central Europe. The different varieties have specialized in quite different plants. So-called cover scale insects such as the comma scale or the introduced San Jose scale, which typically do not secrete honeydew, are found on fruit trees.

    Scale insects, on the other hand, love indoor plants, but are also often found on fruit trees and other deciduous trees. These species in turn secrete honeydew, which is usually colonized by sooty mold fungi. But whatever the type, the countermeasures described here are equally effective for all.

    What do scale insects look like?

    Scale insects can be green, black, or light-colored

    Scale insects are usually very small: Depending on the species, the little creatures reach a length of between 0.6 and six millimeters. The conspicuous protective armor, which only the adult females develop, is characteristic. With this, the pests stick to a suitable feeding place, they also lay their eggs here and raise their larvae - the shell not only protects the female, but also her eggs and larvae. Typically, scale insects do not settle individually, but in regular colonies on leaves and shoots as well as trunks, branches and twigs.

    Incidentally, the male scale insects are completely harmless to the plants, as they do not eat any food as adult animals and have an extremely short lifespan anyway. You might mistake them for small flies, but they don't always make an appearance. The males are not absolutely necessary for the reproduction of the scale insects, since the animals can also reproduce through virgin birth.

    way of life

    A single female scale insect lays up to 2000 eggs a year, which she keeps under her protective shield. The newly hatched larvae are also well protected here, they only leave the cocoon at a later nymph stage. These juveniles are very mobile and easily migrate to other plants. Since the light scale insects can also be carried by the wind outdoors, further infection does not necessarily have to be limited to neighboring plants.

    As soon as a suitable place is found, the female animals attach themselves and form the characteristic shield armor. Since this sticks and the animal also loses all external organs with the exception of its proboscis, the female scale insects are usually immobile. Due to the rapid way in which they reproduce and the high risk of infection, timely control measures are so important - especially since scale insects are quite stubborn and difficult to control.

    Damage caused by scale insect infestation

    Scale insects leave holes in the leaves

    Unfortunately, a scale insect infestation is usually only noticed very late, since both the adult animals and their larvae hide very well at first and thus remain inconspicuous. If the first typical symptoms become noticeable, the infestation is usually very advanced. To prevent this from happening in the first place, you should check endangered plants regularly and thoroughly. The following damage is typical of a scale insect infestation:

    • isolated or accumulated shield armor
    • appear as green or brown bumps
    • woolly or waxy webs on the plant
    • Plant parts and surroundings feel sticky (honeydew)
    • crusted shoots and twigs
    • Leaf spots, mostly light brown, yellow or reddish in color
    • Buds and flowers do not open
    • Leaves cripple, are shed

    Incidentally, symptoms such as leaf spots and shedding as well as short stature and deformed buds and flowers can not only indicate scale insects, but can also occur as a result of other pests or plant diseases. Only the bumps or webs (depending on the type of scale insect) that can occur on almost all parts of the plant are characteristic.

    Particularly endangered plants

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    Scale insects prefer to settle on hard-leaved, evergreen plants, which is why popular indoor plants such as rubber and lemon trees, holly and orchids are particularly at risk. In the garden, the pests particularly like to attach themselves to fruit and ornamental trees, where they can not only be found on the leaves and soft shoots, but also on the trunk, branches and twigs. You can recognize an infestation by the scaly formations that often cover the various parts of the plant in large quantities. The table shows which plant species are particularly endangered.

    indoor plants garden plants
    Asparagus (various) Apple tree (Malus domestica)
    Ferns (various) Pear tree (Pyrus communis)
    window leaf (Monstera) berry bushes (various)
    Ficus (various) Cherry trees (Prunus)
    Flamingo Flower (Anthurium) Peach trees (Prunus persica)
    cacti (various) Plum trees (Prunus domestica)
    Orchids (various) Oleander (Nerium oleander)
    Rubber tree (Ficus elastica) Ivy (Hedera helix)
    palm trees (various) Ferns (various)

    digression

    Mealybugs and mealybugs are also scale insects

    Incidentally, mealybugs and mealybugs also belong to the group of scale insects. These pests, which are up to five millimeters long and mostly pink, white or light brown in color, are not protected by a shield but by a web of wax or a greasy powder-like dust. In these species, the females remain mobile, otherwise untypical for scale insects, and cleverly hide themselves and their clutches in hard-to-reach places such as the leaf axils, the bracts or even in the substrate.

    Causes and Prevention

    Basically, scale insects themselves are just a symptom, as they only attack previously weakened or diseased plants. These are - for example due to an unsuitable location or inadequate care - weakened in their defense and have nothing to oppose the pests. For this reason, scale insects (and many other pests) appear especially after the winter period, when indoor plants are damaged by dry heating air, lack of light and/or too warm a winter period.

    You should also avoid these care mistakes as much as possible:

    • Lack of light / location too dark
    • low humidity / dry air
    • Nutrient deficiency / insufficient fertilization
    • Over-fertilization, especially with nitrogen
    • lack of water
    • waterlogging

    In addition, many indoor plants should not overwinter in the warm living room, but should be placed in a bright and cool place. This applies in particular to Mediterranean plants such as citrus plants, olive trees or oleanders, all of which are frequently attacked by scale insects.

    Is there anything that can be done preventively against scale insects?

    "Prevention is better than cure!"

    You can prevent a scale insect infestation by observing these care instructions, especially for your indoor plants:

    • as much light as possible, install plant lamps if necessary
    • do not hibernate too warm - many Mediterranean plants may only be kept cool to a maximum of 10 to 12 °C
    • balanced supply of water - do not let the substrate dry out, remove excess water from the saucer or planter as soon as possible
    • ensure high humidity, especially when it is warm (summer months, heating period), spray plants regularly or install indoor fountains
    • fertilize regularly but not excessively
    • be rather economical, especially with nitrogenous fertilizers
    • use high-quality substrate, tailored to the respective plant species

    In addition, many indoor plants not only need a lot of light in the summer months, but also air. Therefore, place lemon and olive trees as well as oleanders and co. in a suitable outdoor location, such as on the balcony or terrace.

    What helps? Effectively combat scale insects

    Since scale insects only cause damage to the infested plants, multiply rapidly and quickly infect other plants in the area, immediate and sustained control measures are immensely important. Otherwise, the affected plants will die over time. In addition, the larger their population, the more difficult it is to get rid of scale insects. In this section we present the most effective methods against scale insects.

    First Aid Measures

    Showering will remove most of the scale insects

    Aphids are often driven away with a strong jet of water. This simple method will not work for scale insects, as their shields are glued to them and they are firmly attached to the plant. Instead, you can fight individual animals - such as houseplants - in this way:

    1. Isolate the affected plant immediately.
    2. There must be no other plants nearby.
    3. Place them in a location that is as bright and cool as possible.
    4. Spray them with water and keep the humidity high.
    5. If necessary, cut back heavily infested parts of the plant.
    6. Soak a cotton swab in alcohol.
    7. Press the cotton swab onto each scale insect individually.
    8. Carefully spread the spirit on it.
    9. Gently wipe away any honeydew with a soapy solution.

    If the infestation is too severe, you can also spray the plant instead, for example with a soap and spirit solution. This procedure is easy to handle, especially with individual houseplants, but it takes a lot of time. Do not scratch or scrape the scale insects, as this will keep the eggs and larvae alive and will also spread them throughout the plant.

    Proven home remedies

    If you get a scale insect, you don't have to go straight to the garden store, because fortunately there are various home remedies that are very effective against the pests. It is best to apply this to the plants with the help of a spray bottle, whereby you must not miss even the smallest spot. Please note that some scale insects also like to hide in the leaf axils and bracts. Simply apply the brew to hard-to-reach areas with a brush or cotton swab. Repeat the application until the pests are gone.

    For indoor plants: soap-alcohol lye

    A mixture of (liquid) curd soap and spirit has proven to be practical, especially for indoor plants. To do this, carefully mix 15 milliliters of soap and spirit with one liter of water and fill the mixture into a spray bottle. If possible, use low-lime water such as rainwater or well stale tap water. The liquid should also be at room temperature and never cold or hot - this will damage your plants.

    Also, first test in an inconspicuous place to see whether the plant in question tolerates the mixture at all. Many a sensitive plant also reacts to such home remedies with hanging and/or dropped leaves. However, if it is normal after the test - just wait an hour or two for any reactions - you can finally treat it.

    For garden plants: nettle or wormwood manure

    Of course, you can also treat your garden plants with a soap and alcohol solution, but nettle manure, which can be used in many different ways, is more effective here. This has the advantage of being much gentler on the plants treated with it and also delivering a balanced nutrient cocktail. This also gives the plant a powerful boost for its own defense system. Instead of stinging nettle, you can also prepare and use wormwood manure.

    And this is how you prepare the nettle liquid manure:

    1. Gather a kilogram of fresh leaves and stems.
    2. Prefer nettles before flowering as they contain more active ingredients.
    3. Cut the plant parts as finely as possible.
    4. Put them in a plastic bucket.
    5. Fill it up with ten liters of rain or spring water.
    6. Cover the mixture with an air-permeable cloth or mesh.
    7. This is to prevent animals from falling in there and drowning.
    8. Place the mixture in a partially shaded and warm location.
    9. Stir vigorously daily.

    The liquid manure is ready for use after about eight to ten days. Now filter off the coarse plant parts and fill the liquid into a canister. It will keep for about a week if you seal the canister airtight. For use as a spray, you should dilute the nettle manure with water in a ratio of 1:10 - i. H. to one part liquid manure there are nine parts rain or spring water.

    tips

    Due to their penetrating odor, plant manure is really only recommended for use in the garden. However, you can mitigate the stench a bit by adding a handful of rock flour to the mixture.

    Biological antidotes: voracious beneficial insects against scale insects

    If the scale insects occur in the garden or in the greenhouse, so-called beneficial insects are recommended for targeted control. You can buy these in specialist shops or on the Internet and place them directly on the affected plants. The beneficial insects usually eat the eggs or larvae of the pests, but do not cause any damage to the plants themselves. Once the pests have been eliminated, the beneficial insects usually disappear again. Incidentally, you can also selectively settle them in the garden, so the natural balance is maintained and pests have a harder time establishing themselves from the start.

    However, in a garden that is friendly to beneficial insects, you must not use any sprays (not even home remedies!), as these do not distinguish between pests and beneficial insects. With soapy water and alcohol, they also drive away the desired insects. You should also provide plenty of insect food (e.g. in the form of many umbellifers), because in many cases the larvae of the beneficial insects act as pest controllers, while the adult insects live primarily on pollen and nectar. A cleverly placed insect hotel (€11.33) provides a sought-after shelter.

    If you want to use beneficial insects against the scale insect plague, you should use one of the following types:

    • parasitic wasps
    • ladybug
    • hoverflies
    • lacewings
    • gall midges

    Be sure to follow the manufacturer's instructions for use and quantity recommendations, since using too little or too many beneficial insects will not lead to the desired success.

    Chemicals

    If none of the agents described help, for example because the infestation has already progressed too far, there are still special systemic pesticides. However, their use needs to be carefully considered, especially if you are going to use them in the garden or in the greenhouse. Chemical agents always have negative effects on the environment and thus on the ecological balance.

    In this case, use special sticks or sprays against scale insects, since contact poisons have no effect - the shield armor is too strong for them. Simply stick the sticks into the ground while using the spray as a spray.

    frequently asked Questions

    Are scale insects poisonous to humans?

    You can theoretically eat scale insects

    Typically, scale insects not only suck off the plant sap, but also inject toxic substances into the plant cells. These in turn cause the leaf spots that are characteristic of a severe infestation, which can be brown, red or yellow in color. For humans or pets, however, the pests are harmless and not poisonous.

    Are scale insects dangerous?

    Scale insects are not dangerous in any way to humans or animals. An infestation is only problematic for the affected plants, because the longer and the more the pests romp around on a plant, the more likely it is to be damaged. There is a permanent threat of malformations - for example unsightly spots on the leaves, yellowing flowers and stunted growth - or even the ultimate death of the plant. For this reason, timely and effective control methods are so important.

    How do scale insects spread?

    If your indoor plants are infested with scale insects, the animals were probably brought in by a new plant. Therefore, look out for telltale signs when buying, such as shields on hidden plant parts or waxy excretions. It is better to leave such plants where they are and not take them home with you! If, on the other hand, you receive plants as a gift, first quarantine the newcomer and examine it carefully for characteristic signs.

    Otherwise - for example in the garden - scale insects spread because the young animals emigrate and thus conquer new terrain. An infestation also occurs through wind transmission or through already infected scions (e.g. cuttings from an infected plant in the neighbor's garden).

    Can scale insects fly?

    Female scale insects do not have wings and therefore cannot fly. They don't have any external organs at all, so the adult animals also lack legs and eyes. Male scale insects, on the other hand, have front but no rear wings, so they can fly. They look like flies, but live only a few hours. However, scale insects are not necessarily dependent on sexual reproduction, since the female animals can also reproduce asexually via so-called virgin birth.

    Does frost help against scale insects?

    Some hope that the scale insect plague will get rid of itself in a frosty winter. However, the pests are completely insensitive to cold and survive even the coldest winter - at least when it comes to eggs. These are usually located under the cover of the female scale insect and are well protected from the weather. For this reason it is important that infested plants are also treated in February and other times at the beginning of the growing season so that no larvae and thus no adult scale insects develop from the eggs.

    tips

    Regardless of which control measures you choose: A single application is not enough! In order to actually catch all scale insects as well as the last larva and the last egg, you have to use the remedy several times at intervals of several days and weeks.

Category:

Animals in the garden