Last updated on October 23rd, 2023 at 08:47 pm
Woolly aphids spread in the garden in summer and on houseplants in winter. Although the pests can be clearly identified, they are often first noticed by an extremely annoying feature.
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Mealybugs: the most important facts in a nutshell
Mealybugs are plant pests that suck their sugary sap, causing growth stunting.
Mealybugs sit like small cotton balls in leaf axils, on the bark and under leaves.
As a preventive measure, an optimal location with sufficient light and balanced fertilization is necessary to keep the plants fit.
To combat them are suitable spirit solutions or beneficial insects.
Yuccas get them, cacti or orchids too, and in summer spittlebugs or mealybugs do not stop at garden and tub plants such as hydrangeas, oleanders or citrus plants, albeit less frequently.
Although the plant pests are actually conspicuous and unmistakable, they are often first noticed because of an annoying characteristic – they spill sticky honeydew on the leaves, which then look as if they are covered with shiny clear varnish.
The honeydew is sticky, sugary plant sap that the aphids excrete while sucking on leaves and stems. The sap is low in nutrients, however, and the aphids have to get through plenty of it if they want to get their fill. Excess goes right out the back – as honeydew.
The sugar content makes it a perfect breeding ground for sooty mold, which settles as a black coating on the leaves, depriving the plant of light like extreme sunglasses and weakening it further.
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When pests excrete honeydew, they are so-called phloem suckers – in these conduits, the sugar-containing and thus energy-rich sap is transported from the leaves to all other parts of the plant.
Pests with very short sucking proboscises, such as spider mites, cannot reach these conduction pathways; they feed only on the cell sap and therefore do not produce honeydew. Unfortunately, mere sucking is usually not enough; the little animals also trigger deformation and growth disturbance on the plant with their saliva.
What are mealybugs?
Mealybugs or smear lice belong to a subfamily of scale insects that includes almost 1,000 species worldwide. Depending on the species, the little animals grow to just over a millimeter or even a good centimeter in size. If you see mealybugs on your houseplants in Europe or Central Europe, they are probably long-tailed mealybugs (Pseudococcus longispinus) or citrus mealybugs (Planococcus citri) – the most common species.
Mealybugs secrete a waxy substance and thus seem to literally wrap themselves in a cotton ball. Sounds cozy, but it makes combating the aphids difficult, since the protective covering makes the animals quite insensitive to water, chemical and physical influences. Not good conditions for combating them.
Where mealybugs feel at home, the females can lay 500 to 600 eggs in the leaf axils about every eight weeks, from which the hungry larvae hatch ten days later and start feasting on the leaves and other plant parts.
The larvae of mealybugs are mobile at first, but then they attach themselves and usually stay there. However, there are also more mobile mealybugs that seek out other locations to feed, reproduce and overwinter. These are, for example, members of the genus Phenacoccus.
How can you recognize mealybugs in time?
Mealybugs weaken plants when they suck on leaves, stems or in the soil or substrate, as well as on the roots or root neck. In this case, the animals are also called root lice, which are usually only discovered when repotting. Plants infested with mealybugs weaken, develop yellow leaves and stagnate in growth.
In extreme cases, plants can even die completely because of the tiny mealybugs.
Woolly aphids are clearly recognizable by their wax layer, but you often only become aware of them when the windowsill becomes sticky from the aphids’ excretions.
Only then, when you take a closer look, do you notice the small “cotton balls” in the leaf axils, on the leaf veins, which you might otherwise mistake for a fungal infestation or any residue from watering.
How to control mealybugs?
As soon as you notice an infestation of mealybugs or mealybugs, you should isolate the plants and place them in a cool place. In this way, the mobile stages of the beetles cannot spread to other plants and there will not be a mass infestation on the windowsill. If the mealybug infestation is not yet far advanced and only a few parts of the plant are affected, you can pluck the aphids from the leaf axils with broad tweezers or dip cotton swabs in methylated spirits and wipe the insects away with them. Do this treatment until no more mealybugs appear. This can take up to ten days, as new pests are still hatching from the eggs during this time. If the plants can tolerate pruning, you can also cut off individual infested shoots and dispose of them in the household trash.
Since methylated spirit penetrates the waxy shield of mealybugs, you can also mix it into a home spray remedy: Add a tablespoon of spirit to a quart of water and as much kerosene oil or curd soap. Spray the infested parts of the plant with the mixture – for more sensitive orchids, brush on the solution.
If mealybugs appear as root aphids, first remove the soil or substrate from the roots and then dab off the aphids. Pot the plant in a new pot with fresh soil.
Beneficial insects are suitable for biological control. The use of ichneumon wasps, ladybugs or Australian ladybugs, respectively, or lacewings against mealybugs is possible – if they occur on houseplants or on plants in the greenhouse. In the garden, the beneficial insects would not stay long on the plant on which they are supposed to fight the pests.
The beneficial insects can be ordered from specialized stores as larvae and released on the infested plants. The beneficial insects are completely harmless to pets and other plants.
Those who do not trust home remedies and who do not mind chemicals in the house can also use approved chemical agents against mealybugs. Ideal are agents with full-systemic effect, which are transported further in the plant with the sap flow and thus bypass the wax layer – the aphids simply suck up the poison with the plant sap.
Against the immobile stages of the aphids, oil-based agents are also effective, enclosing all the hit aphids in an air-impermeable shell.
Is it possible to prevent an infestation of mealybugs and mealybugs?
Prevention is better than combating an acute mealybug infestation. Weakened plants are particularly at risk. Provide everything that is good for the plants: proper location with enough light, sufficient but not too much water and regular, but in no case excessive fertilization – especially with nitrogen.
Mealybugs love dry air and weakened plants with nice soft tissue. Therefore, in dry heating air, the pests appear more often, and the little light in winter further weakens the plants.
Check your ornamental plants regularly to detect the little animals in the leaf axils at an early stage. Look under the leaves of the plants and pay special attention to the leaf veins, where the pests like to suck.
Be careful with newly purchased plants, cuttings or even souvenirs – this is how most pests find their way into the home. Houseplants from the garden center can of course carry aphids, but the plants are actually taken out of circulation right away if the staff detects a pest infestation.
You can strengthen houseplants just as you can the plants in the garden with yokes from nettles or horsetail and thus make them fit. However, these remedies are not suitable for combating acute infestations.
However, these home remedies ensure a solid cell structure and make it more difficult for the aphids to infest a plant. A firmer cell wall as a barrier can, under certain circumstances, make the difference between infestation and non-infestation and ensure that the pests do not spread or continue to spread in the first place.